diff --git a/docs/gallery/assets/gn-zone-iterate-hero.webp b/docs/gallery/assets/gn-zone-iterate-hero.webp
index 7a8806e1..52382bb6 100644
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index 04f851b8..ac02789b 100644
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diff --git a/docs/gallery/contact-sheets/gn-zone-iterate-contact-sheet.webp b/docs/gallery/contact-sheets/gn-zone-iterate-contact-sheet.webp
index e3d990b6..1355051e 100644
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diff --git a/docs/gallery/contact-sheets/stone-archway-contact-sheet.webp b/docs/gallery/contact-sheets/stone-archway-contact-sheet.webp
index 472e139a..f6260fb1 100644
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diff --git a/docs/gallery/gn-zone-iterate/index.html b/docs/gallery/gn-zone-iterate/index.html
index 6c268126..eeb86327 100644
--- a/docs/gallery/gn-zone-iterate/index.html
+++ b/docs/gallery/gn-zone-iterate/index.html
@@ -16,13 +16,13 @@
   <meta property="og:image" content="https://tmhsdigital.github.io/Blender-Developer-Tools/gallery/assets/gn-zone-iterate-hero.webp" />
   <meta property="og:image:width" content="1280" />
   <meta property="og:image:height" content="720" />
-  <meta property="og:image:alt" content="Four ochre cubes in a row from a Repeat zone beside a vertical stack of six cyan cubes from a For Each zone." />
+  <meta property="og:image:alt" content="Four brass cubes evenly spaced in a row from a Repeat zone beside a vertical stack of six cyan cubes from a For Each zone." />
   <meta property="og:site_name" content="Blender Developer Tools" />
   <meta name="twitter:card" content="summary_large_image" />
   <meta name="twitter:title" content="gn-zone-iterate — Examples — Blender Developer Tools" />
   <meta name="twitter:description" content="Repeat Zone and For Each Element only iterate after pair_with_output. Evaluated cube counts follow 8 times (1+N) and 8 times P, not tree structure." />
   <meta name="twitter:image" content="https://tmhsdigital.github.io/Blender-Developer-Tools/gallery/assets/gn-zone-iterate-hero.webp" />
-  <meta name="twitter:image:alt" content="Four ochre cubes in a row from a Repeat zone beside a vertical stack of six cyan cubes from a For Each zone." />
+  <meta name="twitter:image:alt" content="Four brass cubes evenly spaced in a row from a Repeat zone beside a vertical stack of six cyan cubes from a For Each zone." />
   <style>
     /* fonts are deployed by the landing build (docs/fonts/) */
     @font-face { font-family: 'Barlow Condensed'; font-weight: 600; font-display: swap;
@@ -268,8 +268,8 @@ <h1>gn-zone-iterate</h1>
     <p>Repeat Zone and For Each Element only iterate after pair_with_output. Evaluated cube counts follow 8 times (1+N) and 8 times P, not tree structure.</p>
   </header>
   <main id="main">
-    <button class="detail-hero" id="heroZoom" type="button" aria-label="View full size: Four ochre cubes in a row from a Repeat zone beside a vertical stack of six cyan cubes from a For Each zone.">
-      <img src="../assets/gn-zone-iterate-hero.webp" alt="Four ochre cubes in a row from a Repeat zone beside a vertical stack of six cyan cubes from a For Each zone." width="1280" height="720" />
+    <button class="detail-hero" id="heroZoom" type="button" aria-label="View full size: Four brass cubes evenly spaced in a row from a Repeat zone beside a vertical stack of six cyan cubes from a For Each zone.">
+      <img src="../assets/gn-zone-iterate-hero.webp" alt="Four brass cubes evenly spaced in a row from a Repeat zone beside a vertical stack of six cyan cubes from a For Each zone." width="1280" height="720" />
     </button>
     <p class="zoom-hint">Rendered headless by the example itself — click to zoom.</p>
     <div class="callout"><span class="tag">witnesses</span> Repeat 32/24 verts/faces with X-centers at k*1.2; For Each 48/36 with Z-centers at i*0.6+0.21. Unpaired evaluates empty; For Each main Geometry passthrough is 6 verts.</div>
@@ -601,6 +601,19 @@ <h2>Source</h2>
     <span class="k">return</span> <span class="s">&quot;BLENDER_EEVEE&quot;</span> <span class="k">if</span> bpy.app.version &gt;= (<span class="n">5</span>, <span class="n">0</span>, <span class="n">0</span>) <span class="k">else</span> <span class="s">&quot;BLENDER_EEVEE_NEXT&quot;</span>
 
 
+<span class="k">def</span> _node_materials(ob):
+    <span class="s">&quot;&quot;&quot;Materials the object&#x27;s Geometry Nodes tree assigns (Set Material nodes).&quot;&quot;&quot;</span>
+    out = []
+    <span class="k">for</span> md <span class="k">in</span> ob.modifiers:
+        <span class="k">if</span> md.type == <span class="s">&quot;NODES&quot;</span> <span class="k">and</span> md.node_group <span class="k">is</span> <span class="k">not</span> <span class="k">None</span>:
+            <span class="k">for</span> node <span class="k">in</span> md.node_group.nodes:
+                <span class="k">if</span> node.bl_idname == <span class="s">&quot;GeometryNodeSetMaterial&quot;</span>:
+                    mat = node.inputs[<span class="s">&quot;Material&quot;</span>].default_value
+                    <span class="k">if</span> mat <span class="k">is</span> <span class="k">not</span> <span class="k">None</span> <span class="k">and</span> mat <span class="k">not</span> <span class="k">in</span> out:
+                        out.append(mat)
+    <span class="k">return</span> out
+
+
 <span class="k">def</span> render_still(rpt, fee, path, engine):
     scene = bpy.context.scene
 
@@ -640,16 +653,32 @@ <h2>Source</h2>
     light(<span class="s">&quot;Key&quot;</span>, (-<span class="n">4.0</span>, -<span class="n">5.0</span>, <span class="n">6.0</span>), <span class="n">520.0</span>, <span class="n">5.0</span>, (<span class="n">1.0</span>, <span class="n">0.96</span>, <span class="n">0.9</span>), (<span class="n">46</span>, <span class="n">0</span>, -<span class="n">35</span>))
     light(<span class="s">&quot;Fill&quot;</span>, (<span class="n">5.0</span>, -<span class="n">3.5</span>, <span class="n">3.0</span>), <span class="n">160.0</span>, <span class="n">9.0</span>, (<span class="n">0.75</span>, <span class="n">0.85</span>, <span class="n">1.0</span>), (<span class="n">62</span>, <span class="n">0</span>, <span class="n">50</span>))
     light(<span class="s">&quot;Wedge&quot;</span>, (<span class="n">2.5</span>, <span class="n">5.5</span>, <span class="n">4.0</span>), <span class="n">360.0</span>, <span class="n">6.0</span>, (<span class="n">1.0</span>, <span class="n">0.76</span>, <span class="n">0.5</span>), (-<span class="n">68</span>, <span class="n">0</span>, <span class="n">190</span>))
-    light(<span class="s">&quot;Glint&quot;</span>, (<span class="n">0.4</span>, -<span class="n">5.2</span>, <span class="n">5.5</span>), <span class="n">700.0</span>, <span class="n">0.9</span>, (<span class="n">1.0</span>, <span class="n">0.92</span>, <span class="n">0.75</span>), (<span class="n">42</span>, <span class="n">0</span>, <span class="n">8</span>))
-
+    <span class="c"># Broad, not a 0.9 m spot: the small Glint blew the top tower cube out</span>
+    <span class="c"># to near-white cyan, the brightest thing in frame by a wide margin.</span>
+    light(<span class="s">&quot;Glint&quot;</span>, (<span class="n">0.4</span>, -<span class="n">5.2</span>, <span class="n">5.5</span>), <span class="n">300.0</span>, <span class="n">3.0</span>, (<span class="n">1.0</span>, <span class="n">0.92</span>, <span class="n">0.75</span>), (<span class="n">42</span>, <span class="n">0</span>, <span class="n">8</span>))
+    <span class="c"># Rim from behind so the cube silhouettes separate from the dark wall.</span>
+    light(<span class="s">&quot;Rim&quot;</span>, (-<span class="n">1.0</span>, <span class="n">4.5</span>, <span class="n">4.5</span>), <span class="n">260.0</span>, <span class="n">4.0</span>, (<span class="n">0.70</span>, <span class="n">0.82</span>, <span class="n">1.0</span>), (-<span class="n">50</span>, <span class="n">0</span>, <span class="n">180</span>))
+
+    <span class="c"># Presentation only: the check never reads materials. 0.85 metallic in a</span>
+    <span class="c"># near-black world reflected near-black, and the brass read as mustard</span>
+    <span class="c"># card. Less metal and a warmer, brighter base let the key shape it.</span>
+    <span class="k">for</span> ob, rough, metal <span class="k">in</span> ((rpt, <span class="n">0.42</span>, <span class="n">0.55</span>), (fee, <span class="n">0.38</span>, <span class="n">0.10</span>)):
+        <span class="k">for</span> mat <span class="k">in</span> _node_materials(ob):
+            bsdf = mat.node_tree.nodes.get(<span class="s">&quot;Principled BSDF&quot;</span>)
+            <span class="k">if</span> bsdf <span class="k">is</span> <span class="k">not</span> <span class="k">None</span>:
+                bsdf.inputs[<span class="s">&quot;Metallic&quot;</span>].default_value = metal
+                bsdf.inputs[<span class="s">&quot;Roughness&quot;</span>].default_value = rough
+
+    <span class="c"># Centred on the pair and more frontal: from (6.6, -9.3) the repeat row</span>
+    <span class="c"># foreshortened into a diagonal and the tower hugged the right edge.</span>
     aim = bpy.data.objects.new(<span class="s">&quot;Aim&quot;</span>, <span class="k">None</span>)
-    aim.location = (<span class="n">0.0</span>, <span class="n">0.0</span>, <span class="n">1.50</span>)
+    aim.location = (-<span class="n">0.10</span>, <span class="n">0.0</span>, <span class="n">1.62</span>)
     aim.hide_render = <span class="k">True</span>
     scene.collection.objects.link(aim)
     cam_data = bpy.data.cameras.new(<span class="s">&quot;Cam&quot;</span>)
     cam_data.lens = <span class="n">50.0</span>
     cam = bpy.data.objects.new(<span class="s">&quot;Cam&quot;</span>, cam_data)
-    cam.location = (<span class="n">6.6</span>, -<span class="n">9.3</span>, <span class="n">3.55</span>)
+    cam.location = (<span class="n">2.7</span>, -<span class="n">10.6</span>, <span class="n">3.1</span>)
     scene.collection.objects.link(cam)
     scene.camera = cam
     track = cam.constraints.new(<span class="s">&quot;TRACK_TO&quot;</span>)
@@ -731,7 +760,7 @@ <h2>Source</h2>
   </main>
   <dialog class="lightbox" id="lightbox" aria-label="Full-size render">
     <button class="lightbox-close" type="button" autofocus>Close</button>
-    <img src="../assets/gn-zone-iterate-hero.webp" alt="Four ochre cubes in a row from a Repeat zone beside a vertical stack of six cyan cubes from a For Each zone." />
+    <img src="../assets/gn-zone-iterate-hero.webp" alt="Four brass cubes evenly spaced in a row from a Repeat zone beside a vertical stack of six cyan cubes from a For Each zone." />
   </dialog>
   <footer>
     <div class="statusbar">
diff --git a/docs/gallery/index.html b/docs/gallery/index.html
index f8682207..fcefb4b9 100644
--- a/docs/gallery/index.html
+++ b/docs/gallery/index.html
@@ -871,7 +871,7 @@ <h2><a href="usd-export-evaluation-mode/">usd-export-evaluation-mode</a></h2>
       </article>
       <article class="card" data-tags="geometry-nodes">
         <a class="card-media" href="gn-zone-iterate/" tabindex="-1" aria-hidden="true">
-          <img src="assets/gn-zone-iterate-hero.webp" alt="Four ochre cubes in a row from a Repeat zone beside a vertical stack of six cyan cubes from a For Each zone." loading="lazy" decoding="async" />
+          <img src="assets/gn-zone-iterate-hero.webp" alt="Four brass cubes evenly spaced in a row from a Repeat zone beside a vertical stack of six cyan cubes from a For Each zone." loading="lazy" decoding="async" />
         </a>
         <div class="card-body">
           <h2><a href="gn-zone-iterate/">gn-zone-iterate</a></h2>
@@ -1201,7 +1201,7 @@ <h2><a href="crate-stack/">crate-stack</a></h2>
       </article>
       <article class="card" data-tags="mesh export showcase">
         <a class="card-media" href="stone-archway/" tabindex="-1" aria-hidden="true">
-          <img src="assets/stone-archway-hero.webp" alt="A freestanding stone archway of coursed piers and a semicircular arch with a keystone." loading="lazy" decoding="async" />
+          <img src="assets/stone-archway-hero.webp" alt="A freestanding grey stone archway of coursed piers and a semicircular arch with a keystone, laid in pale recessed mortar joints." loading="lazy" decoding="async" />
         </a>
         <div class="card-body">
           <h2><a href="stone-archway/">stone-archway</a></h2>
diff --git a/docs/gallery/stone-archway/index.html b/docs/gallery/stone-archway/index.html
index 52bcb061..4a4a204a 100644
--- a/docs/gallery/stone-archway/index.html
+++ b/docs/gallery/stone-archway/index.html
@@ -16,13 +16,13 @@
   <meta property="og:image" content="https://tmhsdigital.github.io/Blender-Developer-Tools/gallery/assets/stone-archway-hero.webp" />
   <meta property="og:image:width" content="1280" />
   <meta property="og:image:height" content="720" />
-  <meta property="og:image:alt" content="A freestanding stone archway of coursed piers and a semicircular arch with a keystone." />
+  <meta property="og:image:alt" content="A freestanding grey stone archway of coursed piers and a semicircular arch with a keystone, laid in pale recessed mortar joints." />
   <meta property="og:site_name" content="Blender Developer Tools" />
   <meta name="twitter:card" content="summary_large_image" />
   <meta name="twitter:title" content="stone-archway — Showcase — Blender Developer Tools" />
   <meta name="twitter:description" content="A procedural masonry archway — coursed piers, projecting imposts, nine voussoirs and a proud keystone — carried through UVs, bake, LOD, collider, and Unity glTF, asserting recomputed budgets rather than an API contract." />
   <meta name="twitter:image" content="https://tmhsdigital.github.io/Blender-Developer-Tools/gallery/assets/stone-archway-hero.webp" />
-  <meta name="twitter:image:alt" content="A freestanding stone archway of coursed piers and a semicircular arch with a keystone." />
+  <meta name="twitter:image:alt" content="A freestanding grey stone archway of coursed piers and a semicircular arch with a keystone, laid in pale recessed mortar joints." />
   <style>
     /* fonts are deployed by the landing build (docs/fonts/) */
     @font-face { font-family: 'Barlow Condensed'; font-weight: 600; font-display: swap;
@@ -268,8 +268,8 @@ <h1>stone-archway</h1>
     <p>A procedural masonry archway — coursed piers, projecting imposts, nine voussoirs and a proud keystone — carried through UVs, bake, LOD, collider, and Unity glTF, asserting recomputed budgets rather than an API contract.</p>
   </header>
   <main id="main">
-    <button class="detail-hero" id="heroZoom" type="button" aria-label="View full size: A freestanding stone archway of coursed piers and a semicircular arch with a keystone.">
-      <img src="../assets/stone-archway-hero.webp" alt="A freestanding stone archway of coursed piers and a semicircular arch with a keystone." width="1280" height="720" />
+    <button class="detail-hero" id="heroZoom" type="button" aria-label="View full size: A freestanding grey stone archway of coursed piers and a semicircular arch with a keystone, laid in pale recessed mortar joints.">
+      <img src="../assets/stone-archway-hero.webp" alt="A freestanding grey stone archway of coursed piers and a semicircular arch with a keystone, laid in pale recessed mortar joints." width="1280" height="720" />
     </button>
     <p class="zoom-hint">Rendered headless by the showcase piece itself — click to zoom.</p>
     <div class="callout"><span class="tag">witnesses</span> Recomputed: 924 tris, two materials with 182 dressed and 364 ashlar faces re-stamped after the chamfer, UVs in 0..1 with zero AABB overlap, outer AABB 1.644×0.510×2.057 m, clear opening 1.203 m, zmin 0, hygiene 0 including zero coplanar disjoint pairs, both piers grounded, the springing joint an overlap, all eight mortar joints at 9.70 mm inside the 6–17 mm band, and every intrados vertex within 0.97 mm of the declared 0.60 m radius over 178°. --off-circle exits 19 on the circle fit; --wide-mortar exits 18 on the joint band.</div>
@@ -278,9 +278,9 @@ <h1>stone-archway</h1>
       <button class="copy-btn" id="copyRun" type="button">Copy</button>
     </div>
     <section class="detail-section md">
-<p>A freestanding masonry arch — two coursed piers, projecting imposts, nine voussoirs turning a semicircle, and a keystone standing proud at the crown. <strong>A showcase piece, not an example</strong> — it witnesses no API contract. It asserts that generated geometry meets declared asset budgets, recomputed from the finished mesh.</p>
+<p>A freestanding masonry arch — two coursed piers, projecting imposts, nine voussoirs turning a semicircle, and a keystone standing proud at the crown, every joint filled with a recessed mortar bed. <strong>A showcase piece, not an example</strong> — it witnesses no API contract. It asserts that generated geometry meets declared asset budgets, recomputed from the finished mesh.</p>
 <h2>What it composes</h2>
-<div class="table-wrap"><table><thead><tr><th scope="col">Shipped content</th><th scope="col">Used for</th></tr></thead><tbody><tr><td><code>skills/mesh-editing-and-bmesh</code></td><td>wedge and box construction, chamfer, UVs in one <code>bmesh</code></td></tr><tr><td><code>skills/procedural-materials-and-shaders</code></td><td>two Principled stone materials with noise-driven weathering</td></tr><tr><td><code>skills/bake-high-to-low</code></td><td>Cycles tangent-space normal bake, high onto low</td></tr><tr><td><code>skills/engine-export-presets</code></td><td>Unity glTF (<code>export_yup=True</code>)</td></tr><tr><td><code>skills/depsgraph-and-evaluated-data</code></td><td>evaluated triangle counts for the LOD ratios</td></tr><tr><td><code>snippets/decimate_to_budget.py</code></td><td>LOD1 / LOD2 COLLAPSE chain</td></tr><tr><td><code>snippets/convex_hull_collider.py</code></td><td>convex collider</td></tr><tr><td><code>snippets/lod_chain.py</code></td><td>LOD naming and ratio pattern</td></tr><tr><td><code>examples/mesh-hygiene-audit</code></td><td>hygiene combinatorics (copied, not imported)</td></tr></tbody></table></div>
+<div class="table-wrap"><table><thead><tr><th scope="col">Shipped content</th><th scope="col">Used for</th></tr></thead><tbody><tr><td><code>skills/mesh-editing-and-bmesh</code></td><td>wedge and box construction, chamfer, UVs in one <code>bmesh</code></td></tr><tr><td><code>skills/procedural-materials-and-shaders</code></td><td>ashlar, dressed stone and mortar: object-space mottling, speckle, bump, per-block tone</td></tr><tr><td><code>skills/bake-high-to-low</code></td><td>Cycles tangent-space normal bake, high onto low</td></tr><tr><td><code>skills/engine-export-presets</code></td><td>Unity glTF (<code>export_yup=True</code>)</td></tr><tr><td><code>skills/depsgraph-and-evaluated-data</code></td><td>evaluated triangle counts for the LOD ratios</td></tr><tr><td><code>snippets/decimate_to_budget.py</code></td><td>LOD1 / LOD2 COLLAPSE chain</td></tr><tr><td><code>snippets/convex_hull_collider.py</code></td><td>convex collider</td></tr><tr><td><code>snippets/lod_chain.py</code></td><td>LOD naming and ratio pattern</td></tr><tr><td><code>examples/mesh-hygiene-audit</code></td><td>hygiene combinatorics (copied, not imported)</td></tr></tbody></table></div>
 <h2>The budget that matters</h2>
 <p>An arch can fail invisibly. Nine wedge blocks laid in a row are still nine wedge blocks; the thing that makes them an arch is that their <strong>intrados vertices sit on a circle</strong>. So the piece recomputes that circle from vertex positions — not from the angles the generator used — and asserts every intrados vertex lands within 4 mm of the declared 0.60 m radius, over an arc spanning at least 168°.</p>
 <p><code>--off-circle</code> is the falsifier built for exactly this. It keeps the angles, the joints, the materials, the triangle count and the bounding box identical, and only wanders the intrados radius by ±18 mm. Every other budget in the piece still passes. Only the circle fit sees it.</p>
@@ -288,22 +288,28 @@ <h3>Measuring it took two corrections</h3>
 <p>The first attempt selected intrados vertices by radius. That swept in the chamfer vertices sitting one bevel-width out on each radial face and reported a 5.1 mm error on a true arch. The fit now runs over the vertices of faces that actually face the springing centre — normal inward in XZ <em>and</em> with a small Y component, which is what excludes the chamfer strips running along the intrados edges.</p>
 <h2>Budgets</h2>
 <p>Declared in the script as named constants, recomputed from the generated mesh. Measured values are from Blender 5.2.1; the cross-version table is at the end.</p>
-<div class="table-wrap"><table><thead><tr><th scope="col">Budget</th><th scope="col">Band</th><th scope="col">Measured</th></tr></thead><tbody><tr><td>Base triangles</td><td>700–2600</td><td>924</td></tr><tr><td>LOD1 ratio</td><td>0.32–0.62</td><td>0.5000</td></tr><tr><td>LOD2 ratio</td><td>0.10–0.35</td><td>0.2121 (5.2) / 0.2186 (4.5, 5.1)</td></tr><tr><td>Material slots</td><td>exactly 2, distinct</td><td>2</td></tr><tr><td>Dressed faces (keystone, imposts, plinth and head courses)</td><td>≥ 100</td><td>182</td></tr><tr><td>Ashlar faces</td><td>≥ 280</td><td>364</td></tr><tr><td>UV bounds</td><td>inside 0..1</td><td>(0.0017, 0.0017)–(0.9983, 0.9983)</td></tr><tr><td>UV AABB overlap</td><td>≤ 1e-5</td><td>0.000000</td></tr><tr><td>Outer AABB</td><td>1.644 × 0.510 × 2.057 m ± 0.020</td><td>1.6440 × 0.5100 × 2.0568</td></tr><tr><td>Clear opening</td><td>1.200 m ± 0.015, measured between the pier faces</td><td>1.2033</td></tr><tr><td>Collider triangles</td><td>≤ 260</td><td>168</td></tr><tr><td>Normal bake</td><td><code>{&#x27;FINISHED&#x27;}</code> with image data</td><td><code>{&#x27;FINISHED&#x27;}</code>, <code>has_data=True</code></td></tr><tr><td>glTF export</td><td>file written, non-empty</td><td>~87 kB</td></tr><tr><td>Hygiene</td><td>all zero</td><td>loose 0/0, non-manifold 0, zero-area 0, doubles 0, n-gons 0, coplanar disjoint pairs 0</td></tr><tr><td>Grounded AABB</td><td>\</td><td>zmin\</td><td>≤ 1e-4</td><td>0.00000</td></tr><tr><td>Pier supports</td><td>2 piers, each base course zmin ≤ 1e-3</td><td>2 at 0.00000</td></tr><tr><td>Keystone proud of the wall face</td><td>≥ 0.020 m</td><td>0.03500</td></tr><tr><td>Springing joint</td><td>overlap, surface gap ≤ 1e-4</td><td>0.00000</td></tr><tr><td>Mortar joints</td><td>every adjacent pair in 0.006–0.017 m</td><td>all eight at 0.00970</td></tr><tr><td>Intrados circle fit</td><td>every vertex within 0.004 m of R = 0.60</td><td>0.00097</td></tr><tr><td>Intrados arc span</td><td>≥ 168°</td><td>178.0°</td></tr></tbody></table></div>
+<div class="table-wrap"><table><thead><tr><th scope="col">Budget</th><th scope="col">Band</th><th scope="col">Measured</th></tr></thead><tbody><tr><td>Base triangles</td><td>950–1450</td><td>1140</td></tr><tr><td>LOD1 ratio</td><td>0.32–0.62</td><td>0.5000</td></tr><tr><td>LOD2 ratio</td><td>0.10–0.35</td><td>0.2140 (5.2) / 0.2193 (4.5, 5.1)</td></tr><tr><td>Material slots</td><td>exactly 3, distinct</td><td>3</td></tr><tr><td>Dressed faces (keystone, imposts, plinth and head courses)</td><td>≥ 100</td><td>182</td></tr><tr><td>Ashlar faces</td><td>≥ 280</td><td>364</td></tr><tr><td>Mortar faces</td><td>≥ 100</td><td>108</td></tr><tr><td>UV bounds</td><td>inside 0..1</td><td>(0.0015, 0.0015)–(0.9985, 0.9985)</td></tr><tr><td>UV AABB overlap</td><td>≤ 1e-5</td><td>0.000000</td></tr><tr><td>Outer AABB</td><td>1.644 × 0.510 × 2.057 m ± 0.020</td><td>1.6440 × 0.5100 × 2.0568</td></tr><tr><td>Clear opening</td><td>1.200 m ± 0.015, measured between the pier faces</td><td>1.2033</td></tr><tr><td>Collider triangles</td><td>≤ 260</td><td>168</td></tr><tr><td>Normal bake</td><td><code>{&#x27;FINISHED&#x27;}</code> with image data</td><td><code>{&#x27;FINISHED&#x27;}</code>, <code>has_data=True</code></td></tr><tr><td>glTF export</td><td>file written, non-empty</td><td>~100 kB</td></tr><tr><td>Hygiene</td><td>all zero</td><td>loose 0/0, non-manifold 0, zero-area 0, doubles 0, n-gons 0, coplanar disjoint pairs 0</td></tr><tr><td>Grounded AABB</td><td>\</td><td>zmin\</td><td>≤ 1e-4</td><td>0.00000</td></tr><tr><td>Pier supports</td><td>2 piers, each base course zmin ≤ 1e-3</td><td>2 at 0.00000</td></tr><tr><td>Keystone proud of the wall face</td><td>≥ 0.020 m</td><td>0.03500</td></tr><tr><td>Springing joint</td><td>overlap, surface gap ≤ 1e-4</td><td>0.00000</td></tr><tr><td>Mortar joints</td><td>every adjacent pair in 0.006–0.017 m</td><td>all eight at 0.00970</td></tr><tr><td>Intrados circle fit</td><td>every vertex within 0.004 m of R = 0.60</td><td>0.00097</td></tr><tr><td>Intrados arc span</td><td>≥ 168°</td><td>178.0°</td></tr><tr><td>Mortar contact</td><td>18 joints, each overlapping exactly 2 stones</td><td>18, all 2</td></tr></tbody></table></div>
 <p>Real-world size: a 1.20 m clear opening under a semicircular head, 1.64 m across the piers and 2.06 m to the top of the keystone — a garden gate arch.</p>
+<h2>Mortar</h2>
+<p>Every joint used to be air. The pier courses stood 7 mm apart and the voussoirs 9.7 mm apart, none of them touching: each pier was a stack of floating blocks, with daylight through every joint in the ground-contact and joint close-ups. The mortar-band budget measured the gaps and passed, because the gaps were the right width. Nothing asked what was in them.</p>
+<p>Each joint now holds a mortar shell sized from the two blocks it sits between (<code>add_mortar</code>): beds between courses and under each impost, and wedges between voussoirs. Each is recessed <code>MORTAR_RECESS</code> (chamfer plus 3 mm) behind the stone faces, so it reads as a raked joint, and bites <code>MORTAR_BITE</code> (1.5 mm) into both blocks. Mortar is added after the chamfer pass and left unchamfered, and <code>classify</code> skips mortar shells, so every stone budget — circle fit, joint band, keystone, supports — still measures stone against stone.</p>
+<p><code>mortar_audit</code> asserts that each of the 18 mortar shells BVH-overlaps exactly two stones. <code>--short-mortar</code> stops every joint 1 mm shy of both blocks, so each shell touches none, and the piece exits 18.</p>
+<h2>Surface</h2>
+<p>The stone used to read as wood. Its noise-driven colour mix streaked at hero scale into long brown grain, and under neutral light it looked like cream plaster. <code>stone_material</code> now samples object space with isotropic noise: mottling for colour, fine speckle driving roughness, and a small bump for pitting. A seeded <code>BlockTone</code> face attribute (<code>paint_blocks</code>) shades each stone differently. Dressed stone is paler and smoother than ashlar; mortar is a flat grey-beige. The baked normal map is chained under the bump (<code>wire_normal</code>) rather than replacing it.</p>
 <h2>Determinism</h2>
-<p>Fixed seed 23; no unseeded randomness. Every measured value above is byte-identical on 4.5.11, 5.1.2 and 5.2.1 <strong>except</strong> LOD2, where <code>DECIMATE COLLAPSE</code> produces 196 triangles on 5.2 and 202 on 4.5 and 5.1. That is why the LOD gate is a ratio band (0.10–0.35, measured 0.2121 and 0.2186) and not an exact count.</p>
+<p>Fixed seed 23; no unseeded randomness. Every measured value above is byte-identical on 4.5.11, 5.1.2 and 5.2.1 <strong>except</strong> LOD2, where <code>DECIMATE COLLAPSE</code> produces 244 triangles on 5.2 and 250 on 4.5 and 5.1. That is why the LOD gate is a ratio band (0.10–0.35, measured 0.2140 and 0.2193) and not an exact count.</p>
 <h2>Falsifiers</h2>
-<p>Each breaks one pipeline stage so a <strong>named</strong> budget fails. All seven were run on 4.5.11, 5.1.2 and 5.2.1 and produced the same exit code on all three.</p>
-<div class="table-wrap"><table><thead><tr><th scope="col">Flag</th><th scope="col">Breaks</th><th scope="col">Exit</th></tr></thead><tbody><tr><td><code>--skip-decimate</code></td><td>drops the DECIMATE modifiers, LOD1 ratio goes to 1.0000</td><td>9</td></tr><tr><td><code>--stray-vert</code></td><td>adds one loose vertex inside the opening, so hygiene catches it rather than the bounding box</td><td>15</td></tr><tr><td><code>--lift-z</code></td><td>lifts the whole mesh 50 mm off the floor</td><td>16</td></tr><tr><td><code>--float-pier</code></td><td>floats one pier 12 mm; the other still grounds the AABB, so only the named-support budget sees it</td><td>16</td></tr><tr><td><code>--sink-keystone</code></td><td>sinks the keystone to a quarter of its projection (8.75 mm) — the imposts still set the Y envelope, so the bounding box is unchanged</td><td>17</td></tr><tr><td><code>--wide-mortar</code></td><td>triples the joint angle, opening every joint to 29.1 mm</td><td>18</td></tr><tr><td><code>--off-circle</code></td><td>wanders the intrados radius ±18 mm while keeping angles, joints and envelope</td><td>19</td></tr></tbody></table></div>
+<p>Each breaks one pipeline stage so a <strong>named</strong> budget fails. All eight were run on 4.5.11, 5.1.2 and 5.2.1 and produced the same exit code on all three.</p>
+<div class="table-wrap"><table><thead><tr><th scope="col">Flag</th><th scope="col">Breaks</th><th scope="col">Exit</th></tr></thead><tbody><tr><td><code>--skip-decimate</code></td><td>drops the DECIMATE modifiers, LOD1 ratio goes to 1.0000</td><td>9</td></tr><tr><td><code>--stray-vert</code></td><td>adds one loose vertex inside the opening, so hygiene catches it rather than the bounding box</td><td>15</td></tr><tr><td><code>--lift-z</code></td><td>lifts the whole mesh 50 mm off the floor</td><td>16</td></tr><tr><td><code>--float-pier</code></td><td>floats one pier 12 mm; the other still grounds the AABB, so only the named-support budget sees it</td><td>16</td></tr><tr><td><code>--sink-keystone</code></td><td>sinks the keystone to a quarter of its projection (8.75 mm) — the imposts still set the Y envelope, so the bounding box is unchanged</td><td>17</td></tr><tr><td><code>--wide-mortar</code></td><td>triples the joint angle, opening every joint to 29.1 mm</td><td>18</td></tr><tr><td><code>--off-circle</code></td><td>wanders the intrados radius ±18 mm while keeping angles, joints and envelope</td><td>19</td></tr><tr><td><code>--short-mortar</code></td><td>stops every mortar joint 1 mm shy of both stones; each of the 18 touches none, mortar-contact budget</td><td>18</td></tr></tbody></table></div>
 <p>Three of these needed the model changed, not the budget:</p>
 <ul><li><strong><code>--sink-keystone</code></strong> originally removed the projection outright, which shrank the Y bounding box by 70 mm and tripped the AABB gate first. The imposts were added so the envelope no longer depends on the keystone — and an impost course is correct masonry the arch was missing anyway.</li><li><strong><code>--off-circle</code></strong> began as <code>--flat-arch</code>, laying the voussoirs as a lintel. That is 0.62 m shorter and fails on the bounding box, proving nothing about the circle fit. Wandering the radius inside the same envelope is the honest version.</li><li><strong><code>--float-pier</code></strong> tripped the z-fight budget rather than the support budget, because the impost was pinned to an absolute height while the courses under it rose into it. The impost now rides on its own pier.</li></ul>
 <h2>Findings the budgets forced</h2>
 <ul><li><strong>The chamfer pass silently repainted the mesh.</strong> <code>bmesh.ops.bevel</code> gives every face it creates <code>material_index</code> 0, so chamfering nineteen blocks left 30 faces on the dressed slot and moved 464 to ashlar. The slot count and the distinct-material check both still passed. Only the per-material face floor caught it, which is exactly the class <code>showcase/README.md</code> warns about. Materials are now re-stamped after the bevel, per block, by nearest recorded centroid.</li><li><strong>The impost landed exactly on the top course.</strong> Same footprint, same plane, two coincident face centres — a z-fight. It now sits on its own mortar bed, which is why the pier lays <code>N_COURSE</code> beds rather than <code>N_COURSE - 1</code>.</li><li><strong><code>find_nearest</code> is unsigned.</strong> A voussoir seated <em>inside</em> the pier head reported a 5.4 mm gap where there was none, because the distance to the host&#x27;s skin is positive from inside too. Joint gaps now test BVH overlap first and return zero when two blocks interpenetrate.</li><li><strong>Joint gaps have to be measured both ways.</strong> The keystone&#x27;s radial faces are wider in Y than its neighbours&#x27;, so every keystone vertex on the joint lies outside the neighbour and read 33 mm instead of the 9.7 mm joint. The metric is the closest approach of the two surfaces, min of both directions.</li></ul>
 <h2>Exit codes</h2>
 <p>File-local and sequential. <code>9</code> is a valid check code; there is no rule against it. <code>1</code> is the FATAL wrapper — a crash, never a named check.</p>
-<div class="table-wrap"><table><thead><tr><th scope="col">Code</th><th scope="col">Meaning</th></tr></thead><tbody><tr><td>0</td><td>Success</td></tr><tr><td>1</td><td>Uncaught exception (FATAL wrapper)</td></tr><tr><td>2</td><td>argparse / usage</td></tr><tr><td>3</td><td>Mesh did not build, or has no UV layer</td></tr><tr><td>4</td><td>Base triangle count outside band</td></tr><tr><td>5</td><td>Material slots, or a material&#x27;s face floor</td></tr><tr><td>6</td><td>UVs outside 0..1</td></tr><tr><td>7</td><td>UV AABB overlap above tolerance</td></tr><tr><td>8</td><td>Outer AABB off declared size</td></tr><tr><td>9</td><td>LOD1 or LOD2 ratio outside band (<code>--skip-decimate</code>)</td></tr><tr><td>10</td><td>Framing gate (<code>examples/gallery_framing.py</code>, render path only)</td></tr><tr><td>11</td><td>Collider triangles above ceiling</td></tr><tr><td>12</td><td>Normal bake failed or produced no image data</td></tr><tr><td>13</td><td>glTF export missing or empty</td></tr><tr><td>14</td><td><code>--output</code> produced no file</td></tr><tr><td>15</td><td>Mesh hygiene (<code>--stray-vert</code>)</td></tr><tr><td>16</td><td>Grounded zmin, or a pier base floating (<code>--lift-z</code>, <code>--float-pier</code>)</td></tr><tr><td>17</td><td>Keystone projection or springing joint (<code>--sink-keystone</code>)</td></tr><tr><td>18</td><td>Mortar joint outside band (<code>--wide-mortar</code>)</td></tr><tr><td>19</td><td>Intrados circle fit, or clear opening (<code>--off-circle</code>)</td></tr></tbody></table></div>
+<div class="table-wrap"><table><thead><tr><th scope="col">Code</th><th scope="col">Meaning</th></tr></thead><tbody><tr><td>0</td><td>Success</td></tr><tr><td>1</td><td>Uncaught exception (FATAL wrapper)</td></tr><tr><td>2</td><td>argparse / usage</td></tr><tr><td>3</td><td>Mesh did not build, or has no UV layer</td></tr><tr><td>4</td><td>Base triangle count outside band</td></tr><tr><td>5</td><td>Material slots, or a material&#x27;s face floor</td></tr><tr><td>6</td><td>UVs outside 0..1</td></tr><tr><td>7</td><td>UV AABB overlap above tolerance</td></tr><tr><td>8</td><td>Outer AABB off declared size</td></tr><tr><td>9</td><td>LOD1 or LOD2 ratio outside band (<code>--skip-decimate</code>)</td></tr><tr><td>10</td><td>Framing gate (<code>examples/gallery_framing.py</code>, render path only)</td></tr><tr><td>11</td><td>Collider triangles above ceiling</td></tr><tr><td>12</td><td>Normal bake failed or produced no image data</td></tr><tr><td>13</td><td>glTF export missing or empty</td></tr><tr><td>14</td><td><code>--output</code> produced no file</td></tr><tr><td>15</td><td>Mesh hygiene (<code>--stray-vert</code>)</td></tr><tr><td>16</td><td>Grounded zmin, or a pier base floating (<code>--lift-z</code>, <code>--float-pier</code>)</td></tr><tr><td>17</td><td>Keystone projection or springing joint (<code>--sink-keystone</code>)</td></tr><tr><td>18</td><td>Mortar joint outside band (<code>--wide-mortar</code>), or a mortar shell not seated in exactly two stones (<code>--short-mortar</code>)</td></tr><tr><td>19</td><td>Intrados circle fit, or clear opening (<code>--off-circle</code>)</td></tr></tbody></table></div>
 <h2>Run it</h2>
-<pre><code># Budget check, no render. ~0.82 s on 4.5, ~0.85 s on 5.1, ~0.98 s on 5.2.
+<pre><code># Budget check, no render. ~1.1 s on 4.5, ~1.2 s on 5.1, ~1.4 s on 5.2.
 blender --background --python stone_archway.py --
 
 # Falsifier: the intrados stops being a circle. Must exit 19.
@@ -316,7 +322,7 @@ <h2>Run it</h2>
 blender --background --python stone_archway.py -- --output arch.webp</code></pre>
 <p>Smoke runs the check-only path. It does not pass <code>--output</code> or any falsifier.</p>
 <h2>Cross-version measurements</h2>
-<div class="table-wrap"><table><thead><tr><th scope="col">Value</th><th scope="col">4.5.11</th><th scope="col">5.1.2</th><th scope="col">5.2.1</th></tr></thead><tbody><tr><td>Base triangles</td><td>924</td><td>924</td><td>924</td></tr><tr><td>LOD1 tris / ratio</td><td>462 / 0.5000</td><td>462 / 0.5000</td><td>462 / 0.5000</td></tr><tr><td>LOD2 tris / ratio</td><td>202 / 0.2186</td><td>202 / 0.2186</td><td>196 / 0.2121</td></tr><tr><td>Face counts (ashlar / dressed)</td><td>364 / 182</td><td>364 / 182</td><td>364 / 182</td></tr><tr><td>Outer AABB</td><td>1.6440 × 0.5100 × 2.0568</td><td>same</td><td>same</td></tr><tr><td>Collider tris</td><td>168</td><td>168</td><td>168</td></tr><tr><td>Intrados deviation</td><td>0.00097</td><td>0.00097</td><td>0.00097</td></tr><tr><td>Mortar joints</td><td>all 0.00970</td><td>all 0.00970</td><td>all 0.00970</td></tr><tr><td>Check wall-clock</td><td>~0.82 s</td><td>~0.85 s</td><td>~0.98 s</td></tr></tbody></table></div>
+<div class="table-wrap"><table><thead><tr><th scope="col">Value</th><th scope="col">4.5.11</th><th scope="col">5.1.2</th><th scope="col">5.2.1</th></tr></thead><tbody><tr><td>Base triangles</td><td>1140</td><td>1140</td><td>1140</td></tr><tr><td>LOD1 tris / ratio</td><td>570 / 0.5000</td><td>570 / 0.5000</td><td>570 / 0.5000</td></tr><tr><td>LOD2 tris / ratio</td><td>250 / 0.2193</td><td>250 / 0.2193</td><td>244 / 0.2140</td></tr><tr><td>Face counts (ashlar / dressed / mortar)</td><td>364 / 182 / 108</td><td>same</td><td>same</td></tr><tr><td>Outer AABB</td><td>1.6440 × 0.5100 × 2.0568</td><td>same</td><td>same</td></tr><tr><td>Collider tris</td><td>168</td><td>168</td><td>168</td></tr><tr><td>Intrados deviation</td><td>0.00097</td><td>0.00097</td><td>0.00097</td></tr><tr><td>Mortar joints</td><td>all 0.00970</td><td>all 0.00970</td><td>all 0.00970</td></tr><tr><td>Mortar contact</td><td>18 × 2 stones</td><td>same</td><td>same</td></tr><tr><td>Check wall-clock</td><td>~1.11 s</td><td>~1.18 s</td><td>~1.37 s</td></tr></tbody></table></div>
     </section>
     <section class="detail-section src">
       <h2>Source</h2>
@@ -328,7 +334,7 @@ <h2>Source</h2>
 
 Asserts budget conformance of a procedural masonry arch: two coursed
 piers, nine voussoirs turning a semicircle, and a proud keystone, carried
-through UVs, two materials, a high-to-low normal bake, an LOD chain, a
+through UVs, three materials (ashlar, dressed stone, mortar), a high-to-low normal bake, an LOD chain, a
 convex collider, and a Unity glTF export.
 
 The budget that matters here is the one an arch can fail invisibly: the
@@ -342,7 +348,8 @@ <h2>Source</h2>
 budget: ``--skip-decimate`` the LOD-ratio band, ``--stray-vert`` mesh
 hygiene, ``--lift-z`` grounded zmin, ``--float-pier`` the named pier
 supports, ``--sink-keystone`` the keystone joint, ``--wide-mortar`` the
-mortar-joint band, ``--off-circle`` the intrados circle fit.
+mortar-joint band, ``--off-circle`` the intrados circle fit,
+``--short-mortar`` the mortar-contact budget.
 
 Fixed seed 23 for course and block weathering. DECIMATE COLLAPSE
 triangle counts are not byte-identical across Blender versions — the LOD
@@ -413,15 +420,15 @@ <h2>Source</h2>
 SPAN_TOL = <span class="n">0.015</span>
 OPENING_W = <span class="n">2.0</span> * R_IN
 
-BASE_TRIS_MIN = <span class="n">700</span>
-BASE_TRIS_MAX = <span class="n">2600</span>
+BASE_TRIS_MIN = <span class="n">950</span>
+BASE_TRIS_MAX = <span class="n">1450</span>
 LOD1_RATIO_MIN = <span class="n">0.32</span>
 LOD1_RATIO_MAX = <span class="n">0.62</span>
 LOD2_RATIO_MIN = <span class="n">0.10</span>
 LOD2_RATIO_MAX = <span class="n">0.35</span>
 LOD1_TARGET = <span class="n">0.50</span>
 LOD2_TARGET = <span class="n">0.22</span>
-MATERIAL_COUNT = <span class="n">2</span>
+MATERIAL_COUNT = <span class="n">3</span>
 UV_EPS = <span class="n">1e-4</span>
 UV_OVERLAP_MAX = <span class="n">1e-5</span>
 COLLIDER_TRIS_MAX = <span class="n">260</span>
@@ -449,6 +456,19 @@ <h2>Source</h2>
 
 ASHLAR_IDX = <span class="n">0</span>
 DRESSED_IDX = <span class="n">1</span>
+MORTAR_IDX = <span class="n">2</span>
+
+<span class="c"># Mortar fills every joint. Each bed or wedge is built from the two blocks</span>
+<span class="c"># it sits between: recessed behind their faces (deeper than the chamfer, so</span>
+<span class="c"># it reads as a raked joint rather than a filled one) and biting into both.</span>
+<span class="c"># Without it every course floated on 7 mm of air and daylight showed</span>
+<span class="c"># through each joint.</span>
+MORTAR_RECESS = CHAMFER + <span class="n">0.003</span>
+MORTAR_BITE = <span class="n">0.0015</span>
+SHORT_MORTAR_CLEAR = <span class="n">0.001</span>
+N_MORTAR = <span class="n">2</span> * N_COURSE + (N_VOUSSOIR - <span class="n">1</span>)
+MORTAR_FACES_MIN = <span class="n">100</span>
+BLOCK_TONE_JITTER = <span class="n">0.25</span>
 
 
 <span class="k">def</span> eevee_engine_id():
@@ -606,6 +626,9 @@ <h2>Source</h2>
     heights = [usable * r / total <span class="k">for</span> r <span class="k">in</span> raw]
     verts = []
     blocks = []
+    <span class="c"># (width, depth, zmin, zmax) per block, bottom up, impost last: what</span>
+    <span class="c"># the mortar beds between them are sized from.</span>
+    stack = []
     z = FLOAT_PIER_LIFT <span class="k">if</span> (float_pier <span class="k">and</span> sign &lt; <span class="n">0</span>) <span class="k">else</span> <span class="n">0.0</span>
     <span class="k">for</span> i, h <span class="k">in</span> enumerate(heights):
         <span class="c"># Courses weather back a little as they rise; the jitter also keeps</span>
@@ -621,6 +644,7 @@ <h2>Source</h2>
         )
         verts.extend(vs)
         blocks.append(block)
+        stack.append((T_V - inset, depth, z, z + h))
         z += h + COURSE_MORTAR
     <span class="c"># The impost rides on the courses rather than sitting at an absolute</span>
     <span class="c"># height: pinned to H_SPRING it stays put while --float-pier lifts the</span>
@@ -633,7 +657,8 @@ <h2>Source</h2>
     )
     verts.extend(vs)
     blocks.append(block)
-    <span class="k">return</span> verts, blocks
+    stack.append((T_V + <span class="n">2.0</span> * IMPOST_OUT, WALL_Y + <span class="n">2.0</span> * IMPOST_PROUD, z, z + IMPOST_H))
+    <span class="k">return</span> verts, blocks, stack
 
 
 <span class="k">def</span> build_arch(bm, rng, off_circle=<span class="k">False</span>, sink_keystone=<span class="k">False</span>, wide_mortar=<span class="k">False</span>):
@@ -643,6 +668,7 @@ <h2>Source</h2>
     cz = H_SPRING - SPRING_BITE
     verts = []
     blocks = []
+    wedges = []
     <span class="k">for</span> k <span class="k">in</span> range(N_VOUSSOIR):
         is_key = k == KEY_INDEX
         widen = KEY_WIDEN <span class="k">if</span> is_key <span class="k">else</span> <span class="n">0.0</span>
@@ -668,7 +694,43 @@ <h2>Source</h2>
         vs, block = add_wedge(bm, cz, a0, a1, r0, r1, hy, mat)
         verts.extend(vs)
         blocks.append(block)
-    <span class="k">return</span> verts, blocks
+        wedges.append((a0, a1, r0, r1, hy))
+    <span class="k">return</span> verts, blocks, wedges
+
+
+<span class="k">def</span> add_mortar(bm, sign, stack, wedges, short=<span class="k">False</span>):
+    <span class="s">&quot;&quot;&quot;Beds between pier courses and wedges between voussoirs.
+
+    Every dimension comes from the two blocks the joint sits between, so a
+    course that weathers back or a voussoir that rises takes its mortar with
+    it. ``short`` stops each joint SHORT_MORTAR_CLEAR shy of both blocks —
+    the falsifier for the mortar-contact budget.
+    &quot;&quot;&quot;</span>
+    bite = -SHORT_MORTAR_CLEAR <span class="k">if</span> short <span class="k">else</span> MORTAR_BITE
+    <span class="k">if</span> stack <span class="k">is</span> <span class="k">not</span> <span class="k">None</span>:
+        x = sign * (R_IN + T_V / <span class="n">2.0</span>)
+        <span class="k">for</span> (w0, d0, _z0, top), (w1, d1, bot, _z1) <span class="k">in</span> zip(stack, stack[<span class="n">1</span>:]):
+            h = (bot - top) + <span class="n">2.0</span> * bite
+            add_box(
+                bm,
+                (x, <span class="n">0.0</span>, <span class="n">0.5</span> * (top + bot)),
+                (min(w0, w1) - <span class="n">2.0</span> * MORTAR_RECESS,
+                 min(d0, d1) - <span class="n">2.0</span> * MORTAR_RECESS, h),
+                MORTAR_IDX,
+            )
+    <span class="k">if</span> wedges <span class="k">is</span> <span class="k">not</span> <span class="k">None</span>:
+        cz = H_SPRING - SPRING_BITE
+        <span class="k">for</span> (_a0, a1, r0a, r1a, hya), (b0, _b1, r0b, r1b, hyb) <span class="k">in</span> zip(wedges, wedges[<span class="n">1</span>:]):
+            ri = max(r0a, r0b) + MORTAR_RECESS
+            <span class="c"># Angular bite taken at the inner radius, so it is never less</span>
+            <span class="c"># than MORTAR_BITE anywhere along the joint.</span>
+            da = bite / ri
+            add_wedge(
+                bm, cz, a1 - da, b0 + da, ri,
+                min(r1a, r1b) - MORTAR_RECESS,
+                min(hya, hyb) - MORTAR_RECESS,
+                MORTAR_IDX,
+            )
 
 
 <span class="k">def</span> build_arch_mesh(
@@ -677,15 +739,18 @@ <h2>Source</h2>
     sink_keystone=<span class="k">False</span>,
     wide_mortar=<span class="k">False</span>,
     float_pier=<span class="k">False</span>,
+    short_mortar=<span class="k">False</span>,
 ):
     rng = random.Random(ARCH_SEED)
     bm = bmesh.new()
     <span class="k">try</span>:
         blocks = []
+        stacks = []
         <span class="k">for</span> sign <span class="k">in</span> (-<span class="n">1.0</span>, <span class="n">1.0</span>):
-            _v, bl = build_pier(bm, sign, rng, float_pier=float_pier)
+            _v, bl, st = build_pier(bm, sign, rng, float_pier=float_pier)
             blocks.extend(bl)
-        _v, bl = build_arch(
+            stacks.append((sign, st))
+        _v, bl, wedges = build_arch(
             bm,
             rng,
             off_circle=off_circle,
@@ -705,6 +770,12 @@ <h2>Source</h2>
                 clamp_overlap=<span class="k">True</span>,
             )
         assign_materials_by_block(bm, blocks)
+        <span class="c"># Mortar after the chamfer: it sits recessed behind the stone and a</span>
+        <span class="c"># chamfer on a 10 mm bed would eat it. It also stays out of the</span>
+        <span class="c"># block re-stamp, which only knows stone.</span>
+        <span class="k">for</span> sign, st <span class="k">in</span> stacks:
+            add_mortar(bm, sign, st, <span class="k">None</span>, short=short_mortar)
+        add_mortar(bm, <span class="n">0.0</span>, <span class="k">None</span>, wedges, short=short_mortar)
         pack_uvs(bm)
         bmesh.ops.recalc_face_normals(bm, faces=list(bm.faces))
         <span class="k">for</span> face <span class="k">in</span> bm.faces:
@@ -714,44 +785,123 @@ <h2>Source</h2>
         me.update()
     <span class="k">finally</span>:
         bm.free()
+    paint_blocks(me)
     obj = bpy.data.objects.new(name, me)
     bpy.context.collection.objects.link(obj)
     <span class="k">return</span> obj
 
 
-<span class="k">def</span> principled(name, color, metallic, roughness, noise_scale=<span class="n">0.0</span>, wear=<span class="k">None</span>):
+<span class="k">def</span> paint_blocks(me):
+    <span class="s">&quot;&quot;&quot;A seeded tone per stone, as the ``BlockTone`` face attribute.
+
+    Nineteen blocks out of one material are one block repeated; a quarried
+    arch has every stone a shade apart. Mortar keeps the neutral 0.5.
+    &quot;&quot;&quot;</span>
+    tone = [<span class="n">0.5</span>] * len(me.polygons)
+    mortar = mortar_verts(me)
+    owner = {}
+    rng = random.Random(ARCH_SEED * <span class="n">17</span>)
+    <span class="k">for</span> g <span class="k">in</span> shells(me):
+        t = <span class="n">0.5</span> <span class="k">if</span> g[<span class="n">0</span>] <span class="k">in</span> mortar <span class="k">else</span> <span class="n">0.5</span> + rng.uniform(-BLOCK_TONE_JITTER, BLOCK_TONE_JITTER)
+        <span class="k">for</span> i <span class="k">in</span> g:
+            owner[i] = t
+    <span class="k">for</span> p <span class="k">in</span> me.polygons:
+        tone[p.index] = owner[p.vertices[<span class="n">0</span>]]
+    attr = me.attributes.new(<span class="s">&quot;BlockTone&quot;</span>, <span class="s">&quot;FLOAT&quot;</span>, <span class="s">&quot;FACE&quot;</span>)
+    attr.data.foreach_set(<span class="s">&quot;value&quot;</span>, tone)
+
+
+<span class="k">def</span> _sock(sockets, identifier):
+    <span class="s">&quot;&quot;&quot;A Mix-node socket by identifier; its A/B/Result names repeat per type.&quot;&quot;&quot;</span>
+    <span class="k">return</span> next(sk <span class="k">for</span> sk <span class="k">in</span> sockets <span class="k">if</span> sk.identifier == identifier)
+
+
+<span class="k">def</span> stone_material(name, light, dark, roughness, mottle, speck, bump):
+    <span class="s">&quot;&quot;&quot;Stone, not timber: isotropic mottling, fine speckle and pitting.
+
+    The old noise-driven mix read as long brown streaks at hero scale, and
+    the ashlar looked like wood grain. Everything here samples object space
+    with isotropic noise, so nothing in the pattern has a direction.
+    &quot;&quot;&quot;</span>
     mat = bpy.data.materials.new(name)
     mat.use_nodes = <span class="k">True</span>
     nt = mat.node_tree
     bsdf = nt.nodes[<span class="s">&quot;Principled BSDF&quot;</span>]
-    bsdf.inputs[<span class="s">&quot;Base Color&quot;</span>].default_value = color
-    bsdf.inputs[<span class="s">&quot;Metallic&quot;</span>].default_value = metallic
-    bsdf.inputs[<span class="s">&quot;Roughness&quot;</span>].default_value = roughness
-    <span class="k">if</span> noise_scale &gt; <span class="n">0.0</span> <span class="k">and</span> wear <span class="k">is</span> <span class="k">not</span> <span class="k">None</span>:
-        tex = nt.nodes.new(<span class="s">&quot;ShaderNodeTexNoise&quot;</span>)
-        tex.inputs[<span class="s">&quot;Scale&quot;</span>].default_value = noise_scale
-        tex.inputs[<span class="s">&quot;Detail&quot;</span>].default_value = <span class="n">9.0</span>
-        tex.inputs[<span class="s">&quot;Roughness&quot;</span>].default_value = <span class="n">0.6</span>
-        mix = nt.nodes.new(<span class="s">&quot;ShaderNodeMix&quot;</span>)
-        mix.data_type = <span class="s">&quot;RGBA&quot;</span>
-        mix.inputs[<span class="s">&quot;A&quot;</span>].default_value = color
-        mix.inputs[<span class="s">&quot;B&quot;</span>].default_value = wear
-        fac = mix.inputs.get(<span class="s">&quot;Factor&quot;</span>) <span class="k">or</span> mix.inputs.get(<span class="s">&quot;Fac&quot;</span>)
-        nt.links.new(tex.outputs[<span class="s">&quot;Fac&quot;</span>], fac)
-        nt.links.new(mix.outputs[<span class="s">&quot;Result&quot;</span>], bsdf.inputs[<span class="s">&quot;Base Color&quot;</span>])
-        rmix = nt.nodes.new(<span class="s">&quot;ShaderNodeMix&quot;</span>)
-        rmix.data_type = <span class="s">&quot;FLOAT&quot;</span>
-        rmix.inputs[<span class="s">&quot;A&quot;</span>].default_value = roughness
-        rmix.inputs[<span class="s">&quot;B&quot;</span>].default_value = min(<span class="n">1.0</span>, roughness + <span class="n">0.16</span>)
-        rfac = rmix.inputs.get(<span class="s">&quot;Factor&quot;</span>) <span class="k">or</span> rmix.inputs.get(<span class="s">&quot;Fac&quot;</span>)
-        nt.links.new(tex.outputs[<span class="s">&quot;Fac&quot;</span>], rfac)
-        nt.links.new(rmix.outputs[<span class="s">&quot;Result&quot;</span>], bsdf.inputs[<span class="s">&quot;Roughness&quot;</span>])
+    coord = nt.nodes.new(<span class="s">&quot;ShaderNodeTexCoord&quot;</span>)
+    mot = nt.nodes.new(<span class="s">&quot;ShaderNodeTexNoise&quot;</span>)
+    mot.inputs[<span class="s">&quot;Scale&quot;</span>].default_value = mottle
+    mot.inputs[<span class="s">&quot;Detail&quot;</span>].default_value = <span class="n">4.0</span>
+    mot.inputs[<span class="s">&quot;Roughness&quot;</span>].default_value = <span class="n">0.55</span>
+    nt.links.new(coord.outputs[<span class="s">&quot;Object&quot;</span>], mot.inputs[<span class="s">&quot;Vector&quot;</span>])
+    ramp = nt.nodes.new(<span class="s">&quot;ShaderNodeValToRGB&quot;</span>)
+    ramp.color_ramp.elements[<span class="n">0</span>].position = <span class="n">0.32</span>
+    ramp.color_ramp.elements[<span class="n">0</span>].color = dark
+    ramp.color_ramp.elements[<span class="n">1</span>].position = <span class="n">0.70</span>
+    ramp.color_ramp.elements[<span class="n">1</span>].color = light
+    nt.links.new(mot.outputs[<span class="s">&quot;Fac&quot;</span>], ramp.inputs[<span class="s">&quot;Fac&quot;</span>])
+    spk = nt.nodes.new(<span class="s">&quot;ShaderNodeTexNoise&quot;</span>)
+    spk.inputs[<span class="s">&quot;Scale&quot;</span>].default_value = speck
+    spk.inputs[<span class="s">&quot;Detail&quot;</span>].default_value = <span class="n">2.0</span>
+    nt.links.new(coord.outputs[<span class="s">&quot;Object&quot;</span>], spk.inputs[<span class="s">&quot;Vector&quot;</span>])
+    gain = nt.nodes.new(<span class="s">&quot;ShaderNodeMapRange&quot;</span>)
+    gain.inputs[<span class="s">&quot;To Min&quot;</span>].default_value = <span class="n">0.82</span>
+    gain.inputs[<span class="s">&quot;To Max&quot;</span>].default_value = <span class="n">1.12</span>
+    nt.links.new(spk.outputs[<span class="s">&quot;Fac&quot;</span>], gain.inputs[<span class="s">&quot;Value&quot;</span>])
+    mix = nt.nodes.new(<span class="s">&quot;ShaderNodeMix&quot;</span>)
+    mix.data_type = <span class="s">&quot;RGBA&quot;</span>
+    mix.blend_type = <span class="s">&quot;MULTIPLY&quot;</span>
+    _sock(mix.inputs, <span class="s">&quot;Factor_Float&quot;</span>).default_value = <span class="n">1.0</span>
+    nt.links.new(ramp.outputs[<span class="s">&quot;Color&quot;</span>], _sock(mix.inputs, <span class="s">&quot;A_Color&quot;</span>))
+    nt.links.new(gain.outputs[<span class="s">&quot;Result&quot;</span>], _sock(mix.inputs, <span class="s">&quot;B_Color&quot;</span>))
+    <span class="c"># Per-stone shade from the BlockTone face attribute (paint_blocks).</span>
+    tone = nt.nodes.new(<span class="s">&quot;ShaderNodeAttribute&quot;</span>)
+    tone.attribute_name = <span class="s">&quot;BlockTone&quot;</span>
+    shade = nt.nodes.new(<span class="s">&quot;ShaderNodeMath&quot;</span>)
+    shade.operation = <span class="s">&quot;MULTIPLY_ADD&quot;</span>
+    shade.inputs[<span class="n">1</span>].default_value = <span class="n">0.8</span>
+    shade.inputs[<span class="n">2</span>].default_value = <span class="n">0.6</span>
+    nt.links.new(tone.outputs[<span class="s">&quot;Fac&quot;</span>], shade.inputs[<span class="n">0</span>])
+    mix2 = nt.nodes.new(<span class="s">&quot;ShaderNodeMix&quot;</span>)
+    mix2.data_type = <span class="s">&quot;RGBA&quot;</span>
+    mix2.blend_type = <span class="s">&quot;MULTIPLY&quot;</span>
+    _sock(mix2.inputs, <span class="s">&quot;Factor_Float&quot;</span>).default_value = <span class="n">1.0</span>
+    nt.links.new(_sock(mix.outputs, <span class="s">&quot;Result_Color&quot;</span>), _sock(mix2.inputs, <span class="s">&quot;A_Color&quot;</span>))
+    nt.links.new(shade.outputs[<span class="s">&quot;Value&quot;</span>], _sock(mix2.inputs, <span class="s">&quot;B_Color&quot;</span>))
+    nt.links.new(_sock(mix2.outputs, <span class="s">&quot;Result_Color&quot;</span>), bsdf.inputs[<span class="s">&quot;Base Color&quot;</span>])
+    rough = nt.nodes.new(<span class="s">&quot;ShaderNodeMapRange&quot;</span>)
+    rough.inputs[<span class="s">&quot;To Min&quot;</span>].default_value = roughness - <span class="n">0.06</span>
+    rough.inputs[<span class="s">&quot;To Max&quot;</span>].default_value = min(<span class="n">1.0</span>, roughness + <span class="n">0.08</span>)
+    nt.links.new(spk.outputs[<span class="s">&quot;Fac&quot;</span>], rough.inputs[<span class="s">&quot;Value&quot;</span>])
+    nt.links.new(rough.outputs[<span class="s">&quot;Result&quot;</span>], bsdf.inputs[<span class="s">&quot;Roughness&quot;</span>])
+    <span class="k">if</span> bump &gt; <span class="n">0.0</span>:
+        bmp = nt.nodes.new(<span class="s">&quot;ShaderNodeBump&quot;</span>)
+        bmp.inputs[<span class="s">&quot;Strength&quot;</span>].default_value = bump
+        bmp.inputs[<span class="s">&quot;Distance&quot;</span>].default_value = <span class="n">0.002</span>
+        nt.links.new(spk.outputs[<span class="s">&quot;Fac&quot;</span>], bmp.inputs[<span class="s">&quot;Height&quot;</span>])
+        nt.links.new(bmp.outputs[<span class="s">&quot;Normal&quot;</span>], bsdf.inputs[<span class="s">&quot;Normal&quot;</span>])
     <span class="k">return</span> mat
 
 
-<span class="k">def</span> assign_slots(obj, ashlar, dressed):
+<span class="k">def</span> arch_materials():
+    <span class="s">&quot;&quot;&quot;(ashlar, dressed, mortar): shared by the check, the render and inspection.&quot;&quot;&quot;</span>
+    ashlar = stone_material(
+        <span class="s">&quot;ArchAshlar&quot;</span>, (<span class="n">0.40</span>, <span class="n">0.355</span>, <span class="n">0.285</span>, <span class="n">1.0</span>), (<span class="n">0.235</span>, <span class="n">0.205</span>, <span class="n">0.160</span>, <span class="n">1.0</span>),
+        <span class="n">0.86</span>, mottle=<span class="n">5.0</span>, speck=<span class="n">140.0</span>, bump=<span class="n">0.30</span>,
+    )
+    dressed = stone_material(
+        <span class="s">&quot;ArchDressed&quot;</span>, (<span class="n">0.56</span>, <span class="n">0.50</span>, <span class="n">0.405</span>, <span class="n">1.0</span>), (<span class="n">0.40</span>, <span class="n">0.355</span>, <span class="n">0.285</span>, <span class="n">1.0</span>),
+        <span class="n">0.66</span>, mottle=<span class="n">3.0</span>, speck=<span class="n">220.0</span>, bump=<span class="n">0.12</span>,
+    )
+    mortar = stone_material(
+        <span class="s">&quot;ArchMortar&quot;</span>, (<span class="n">0.50</span>, <span class="n">0.485</span>, <span class="n">0.450</span>, <span class="n">1.0</span>), (<span class="n">0.40</span>, <span class="n">0.385</span>, <span class="n">0.355</span>, <span class="n">1.0</span>),
+        <span class="n">0.95</span>, mottle=<span class="n">12.0</span>, speck=<span class="n">300.0</span>, bump=<span class="n">0.0</span>,
+    )
+    <span class="k">return</span> ashlar, dressed, mortar
+
+
+<span class="k">def</span> assign_slots(obj, ashlar, dressed, mortar):
     mats = obj.data.materials
-    <span class="k">for</span> i, mat <span class="k">in</span> enumerate((ashlar, dressed)):
+    <span class="k">for</span> i, mat <span class="k">in</span> enumerate((ashlar, dressed, mortar)):
         <span class="k">if</span> i &lt; len(mats):
             mats[i] = mat
         <span class="k">else</span>:
@@ -947,10 +1097,25 @@ <h2>Source</h2>
     <span class="k">return</span> best
 
 
+<span class="k">def</span> mortar_verts(me):
+    <span class="s">&quot;&quot;&quot;Vertices of mortar faces. Mortar is its own shells; stone budgets skip it.&quot;&quot;&quot;</span>
+    <span class="k">return</span> {
+        i <span class="k">for</span> p <span class="k">in</span> me.polygons <span class="k">if</span> p.material_index == MORTAR_IDX <span class="k">for</span> i <span class="k">in</span> p.vertices
+    }
+
+
 <span class="k">def</span> classify(me):
-    <span class="s">&quot;&quot;&quot;Name the shells: pier courses by side, voussoirs by crown angle.&quot;&quot;&quot;</span>
+    <span class="s">&quot;&quot;&quot;Name the stone shells: pier courses by side, voussoirs by crown angle.
+
+    Mortar shells are skipped. Left in, a pier bed classifies as a course
+    and a voussoir wedge as a voussoir, and every stone budget after this
+    measures the wrong neighbours.
+    &quot;&quot;&quot;</span>
     out = {<span class="s">&quot;left&quot;</span>: [], <span class="s">&quot;right&quot;</span>: [], <span class="s">&quot;voussoirs&quot;</span>: []}
+    mortar = mortar_verts(me)
     <span class="k">for</span> g <span class="k">in</span> shells(me):
+        <span class="k">if</span> g[<span class="n">0</span>] <span class="k">in</span> mortar:
+            <span class="k">continue</span>
         pts = [me.vertices[i].co <span class="k">for</span> i <span class="k">in</span> g]
         zmin = min(p.z <span class="k">for</span> p <span class="k">in</span> pts)
         zmax = max(p.z <span class="k">for</span> p <span class="k">in</span> pts)
@@ -1077,6 +1242,31 @@ <h2>Source</h2>
     }
 
 
+<span class="k">def</span> mortar_audit(me):
+    <span class="s">&quot;&quot;&quot;Every mortar shell must be seated in exactly two stones.
+
+    A joint that touches one stone is a bed left hanging; one that touches
+    none is the air gap the mortar exists to fill. Overlap is the metric:
+    each bed bites MORTAR_BITE into both blocks by construction, so the
+    BVH trees must intersect, and a bed that stops short of a block does
+    not.
+    &quot;&quot;&quot;</span>
+    mortar = mortar_verts(me)
+    stone_trees, mortar_trees = [], []
+    <span class="k">for</span> g <span class="k">in</span> shells(me):
+        <span class="k">if</span> len(g) &lt; <span class="n">4</span>:
+            <span class="k">continue</span>
+        (mortar_trees <span class="k">if</span> g[<span class="n">0</span>] <span class="k">in</span> mortar <span class="k">else</span> stone_trees).append(shell_tree(me, g))
+    seats = []
+    <span class="k">for</span> mt <span class="k">in</span> mortar_trees:
+        seats.append(sum(<span class="n">1</span> <span class="k">for</span> st <span class="k">in</span> stone_trees <span class="k">if</span> st <span class="k">is</span> <span class="k">not</span> <span class="k">None</span> <span class="k">and</span> mt.overlap(st)))
+    <span class="k">return</span> {
+        <span class="s">&quot;n&quot;</span>: len(mortar_trees),
+        <span class="s">&quot;seat_min&quot;</span>: min(seats, default=<span class="n">0</span>),
+        <span class="s">&quot;seat_max&quot;</span>: max(seats, default=<span class="n">0</span>),
+    }
+
+
 <span class="k">def</span> opening_audit(me):
     <span class="s">&quot;&quot;&quot;Clear opening width at mid-pier height, measured from vertices.&quot;&quot;&quot;</span>
     <span class="c"># Band stops clear of the impost, which projects inboard of the pier</span>
@@ -1201,6 +1391,7 @@ <h2>Source</h2>
     sink_keystone=<span class="k">False</span>,
     wide_mortar=<span class="k">False</span>,
     off_circle=<span class="k">False</span>,
+    short_mortar=<span class="k">False</span>,
 ):
     bpy.ops.wm.read_factory_settings(use_empty=<span class="k">True</span>)
     flags = dict(
@@ -1208,20 +1399,14 @@ <h2>Source</h2>
         sink_keystone=sink_keystone,
         wide_mortar=wide_mortar,
         float_pier=float_pier,
+        short_mortar=short_mortar,
     )
     nothing = (<span class="k">None</span>,) * <span class="n">5</span>
     low = build_arch_mesh(<span class="s">&quot;ArchLow&quot;</span>, **flags)
     high = build_arch_mesh(<span class="s">&quot;ArchHigh&quot;</span>, **flags)
-    ashlar = principled(
-        <span class="s">&quot;ArchAshlar&quot;</span>, (<span class="n">0.300</span>, <span class="n">0.219</span>, <span class="n">0.126</span>, <span class="n">1.0</span>), <span class="n">0.0</span>, <span class="n">0.80</span>,
-        noise_scale=<span class="n">14.0</span>, wear=(<span class="n">0.168</span>, <span class="n">0.113</span>, <span class="n">0.055</span>, <span class="n">1.0</span>),
-    )
-    dressed = principled(
-        <span class="s">&quot;ArchDressed&quot;</span>, (<span class="n">0.452</span>, <span class="n">0.348</span>, <span class="n">0.205</span>, <span class="n">1.0</span>), <span class="n">0.0</span>, <span class="n">0.62</span>,
-        noise_scale=<span class="n">8.0</span>, wear=(<span class="n">0.262</span>, <span class="n">0.196</span>, <span class="n">0.108</span>, <span class="n">1.0</span>),
-    )
-    assign_slots(low, ashlar, dressed)
-    assign_slots(high, ashlar, dressed)
+    ashlar, dressed, mortar = arch_materials()
+    assign_slots(low, ashlar, dressed, mortar)
+    assign_slots(high, ashlar, dressed, mortar)
     <span class="k">if</span> stray_vert:
         add_stray_vert(low.data)
     <span class="k">if</span> lift_z:
@@ -1269,11 +1454,16 @@ <h2>Source</h2>
         os.remove(export_path)
     export_unity(export_path, [low, collider])
     export_size = os.path.getsize(export_path) <span class="k">if</span> os.path.isfile(export_path) <span class="k">else</span> <span class="n">0</span>
+    <span class="c"># Blender points TMPDIR at its own temp preference, which on a portable</span>
+    <span class="c"># build is the working directory, so the export must not outlive this.</span>
+    <span class="k">if</span> os.path.isfile(export_path):
+        os.remove(export_path)
 
     hyg = hygiene_audit(low.data)
     zf = zfight_pairs(low.data)
     ar = arch_audit(low.data)
     opening = opening_audit(low.data)
+    mo = mortar_audit(low.data)
 
     print(<span class="s">f&quot;</span><span class="s">blender=</span>{tuple(bpy.app.version)}<span class="s"> skip_decimate=</span>{skip_decimate}<span class="s">&quot;</span>)
     print(<span class="s">f&quot;</span><span class="s">measured mat_index_counts=</span>{idx_counts}<span class="s">&quot;</span>)
@@ -1305,6 +1495,9 @@ <h2>Source</h2>
         <span class="s">f&quot;</span><span class="s">key_proud=</span>{ar[<span class="s">&#x27;key_proud&#x27;</span>]:<span class="s">.5f</span>}<span class="s"> spring_gap=</span>{ar[<span class="s">&#x27;spring_gap&#x27;</span>]:<span class="s">.5f</span>}<span class="s"> </span><span class="s">&quot;</span>
         <span class="s">f&quot;</span><span class="s">pier_worst=</span>{ar[<span class="s">&#x27;pier_worst&#x27;</span>]:<span class="s">.5f</span>}<span class="s"> gaps=</span>{ar[<span class="s">&#x27;gaps&#x27;</span>]}<span class="s">&quot;</span>
     )
+    print(
+        <span class="s">f&quot;</span><span class="s">measured mortar n=</span>{mo[<span class="s">&#x27;n&#x27;</span>]}<span class="s"> seats=[</span>{mo[<span class="s">&#x27;seat_min&#x27;</span>]}<span class="s">, </span>{mo[<span class="s">&#x27;seat_max&#x27;</span>]}<span class="s">]</span><span class="s">&quot;</span>
+    )
 
     <span class="k">if</span> <span class="k">not</span> (BASE_TRIS_MIN &lt;= base_tris &lt;= BASE_TRIS_MAX):
         <span class="k">return</span> (fail(
@@ -1322,6 +1515,10 @@ <h2>Source</h2>
         <span class="k">return</span> (fail(
             <span class="s">f&quot;</span><span class="s">ashlar faces </span>{idx_counts.get(ASHLAR_IDX, <span class="n">0</span>)}<span class="s"> &lt; </span>{ASHLAR_FACES_MIN}<span class="s">&quot;</span>, <span class="n">5</span>
         ),) + nothing
+    <span class="k">if</span> idx_counts.get(MORTAR_IDX, <span class="n">0</span>) &lt; MORTAR_FACES_MIN:
+        <span class="k">return</span> (fail(
+            <span class="s">f&quot;</span><span class="s">mortar faces </span>{idx_counts.get(MORTAR_IDX, <span class="n">0</span>)}<span class="s"> &lt; </span>{MORTAR_FACES_MIN}<span class="s">&quot;</span>, <span class="n">5</span>
+        ),) + nothing
     <span class="k">if</span> u0 &lt; -UV_EPS <span class="k">or</span> v0 &lt; -UV_EPS <span class="k">or</span> u1 &gt; <span class="n">1.0</span> + UV_EPS <span class="k">or</span> v1 &gt; <span class="n">1.0</span> + UV_EPS:
         <span class="k">return</span> (fail(
             <span class="s">f&quot;</span><span class="s">UVs outside 0..1: (</span>{u0:<span class="s">.4f</span>}<span class="s">,</span>{v0:<span class="s">.4f</span>}<span class="s">)-(</span>{u1:<span class="s">.4f</span>}<span class="s">,</span>{v1:<span class="s">.4f</span>}<span class="s">)</span><span class="s">&quot;</span>, <span class="n">6</span>
@@ -1384,6 +1581,12 @@ <h2>Source</h2>
             <span class="s">f&quot;</span><span class="s">mortar joints (</span>{ar[<span class="s">&#x27;gap_min&#x27;</span>]:<span class="s">.5f</span>}<span class="s">, </span>{ar[<span class="s">&#x27;gap_max&#x27;</span>]:<span class="s">.5f</span>}<span class="s">) outside </span><span class="s">&quot;</span>
             <span class="s">f&quot;</span><span class="s">[</span>{MORTAR_MIN}<span class="s">, </span>{MORTAR_MAX}<span class="s">] (--wide-mortar is the designed fail)</span><span class="s">&quot;</span>, <span class="n">18</span>
         ),) + nothing
+    <span class="k">if</span> mo[<span class="s">&quot;n&quot;</span>] != N_MORTAR <span class="k">or</span> mo[<span class="s">&quot;seat_min&quot;</span>] != <span class="n">2</span> <span class="k">or</span> mo[<span class="s">&quot;seat_max&quot;</span>] != <span class="n">2</span>:
+        <span class="k">return</span> (fail(
+            <span class="s">f&quot;</span><span class="s">mortar contact: </span>{mo[<span class="s">&#x27;n&#x27;</span>]}<span class="s"> of </span>{N_MORTAR}<span class="s"> joints, stones seated per </span><span class="s">&quot;</span>
+            <span class="s">f&quot;</span><span class="s">joint [</span>{mo[<span class="s">&#x27;seat_min&#x27;</span>]}<span class="s">, </span>{mo[<span class="s">&#x27;seat_max&#x27;</span>]}<span class="s">], need exactly 2 </span><span class="s">&quot;</span>
+            <span class="s">&quot;(--short-mortar is the designed fail)&quot;</span>, <span class="n">18</span>
+        ),) + nothing
     <span class="k">if</span> ar[<span class="s">&quot;arc_dev&quot;</span>] &gt; ARC_TOL <span class="k">or</span> ar[<span class="s">&quot;arc_span&quot;</span>] &lt; ARC_SPAN_MIN:
         <span class="k">return</span> (fail(
             <span class="s">f&quot;</span><span class="s">intrados off circle by </span>{ar[<span class="s">&#x27;arc_dev&#x27;</span>]:<span class="s">.5f</span>}<span class="s"> &gt; </span>{ARC_TOL}<span class="s"> or spans </span><span class="s">&quot;</span>
@@ -1399,12 +1602,17 @@ <h2>Source</h2>
 
 
 <span class="k">def</span> wire_normal(mat, tex):
+    <span class="s">&quot;&quot;&quot;Baked normal map into the BSDF, under the pitting bump if there is one.&quot;&quot;&quot;</span>
     nt = mat.node_tree
     bsdf = nt.nodes[<span class="s">&quot;Principled BSDF&quot;</span>]
     nrm = nt.nodes.new(<span class="s">&quot;ShaderNodeNormalMap&quot;</span>)
     nrm.inputs[<span class="s">&quot;Strength&quot;</span>].default_value = <span class="n">1.0</span>
     nt.links.new(tex.outputs[<span class="s">&quot;Color&quot;</span>], nrm.inputs[<span class="s">&quot;Color&quot;</span>])
-    nt.links.new(nrm.outputs[<span class="s">&quot;Normal&quot;</span>], bsdf.inputs[<span class="s">&quot;Normal&quot;</span>])
+    bump = next((n <span class="k">for</span> n <span class="k">in</span> nt.nodes <span class="k">if</span> n.bl_idname == <span class="s">&quot;ShaderNodeBump&quot;</span>), <span class="k">None</span>)
+    <span class="k">if</span> bump <span class="k">is</span> <span class="k">not</span> <span class="k">None</span>:
+        nt.links.new(nrm.outputs[<span class="s">&quot;Normal&quot;</span>], bump.inputs[<span class="s">&quot;Normal&quot;</span>])
+    <span class="k">else</span>:
+        nt.links.new(nrm.outputs[<span class="s">&quot;Normal&quot;</span>], bsdf.inputs[<span class="s">&quot;Normal&quot;</span>])
 
 
 <span class="k">def</span> render_still(low, ashlar, tex, path, engine):
@@ -1515,6 +1723,7 @@ <h2>Source</h2>
     p.add_argument(<span class="s">&quot;--sink-keystone&quot;</span>, action=<span class="s">&quot;store_true&quot;</span>)
     p.add_argument(<span class="s">&quot;--wide-mortar&quot;</span>, action=<span class="s">&quot;store_true&quot;</span>)
     p.add_argument(<span class="s">&quot;--off-circle&quot;</span>, action=<span class="s">&quot;store_true&quot;</span>)
+    p.add_argument(<span class="s">&quot;--short-mortar&quot;</span>, action=<span class="s">&quot;store_true&quot;</span>)
     args = p.parse_args(argv)
 
     code, low, _high, ashlar, tex, _col = check(
@@ -1525,6 +1734,7 @@ <h2>Source</h2>
         sink_keystone=args.sink_keystone,
         wide_mortar=args.wide_mortar,
         off_circle=args.off_circle,
+        short_mortar=args.short_mortar,
     )
     <span class="k">if</span> code:
         <span class="k">return</span> code
@@ -1549,7 +1759,7 @@ <h2>Source</h2>
   </main>
   <dialog class="lightbox" id="lightbox" aria-label="Full-size render">
     <button class="lightbox-close" type="button" autofocus>Close</button>
-    <img src="../assets/stone-archway-hero.webp" alt="A freestanding stone archway of coursed piers and a semicircular arch with a keystone." />
+    <img src="../assets/stone-archway-hero.webp" alt="A freestanding grey stone archway of coursed piers and a semicircular arch with a keystone, laid in pale recessed mortar joints." />
   </dialog>
   <footer>
     <div class="statusbar">
diff --git a/examples/coincident-vert-weld/README.md b/examples/coincident-vert-weld/README.md
index 2b9bfffa..c083f059 100644
--- a/examples/coincident-vert-weld/README.md
+++ b/examples/coincident-vert-weld/README.md
@@ -8,23 +8,62 @@ Inverse of [`degenerate-bevel-weld`](../degenerate-bevel-weld/)
 solid). Neighbor of [`gltf-export-roundtrip`](../gltf-export-roundtrip/)
 (kit-bash face-plane welds on export).
 
-**Why this pathology:** coincident shells are still manifold (every
-edge borders 2 faces). Hygiene can pass. The engine trap is extra
-triangles on disk.
+## The contract
+
+A mesh holding two coincident shells is still **manifold**: every edge
+borders exactly two faces, because each shell is closed on its own. A
+hygiene check that only counts non-manifold edges reports 0 and passes.
+The glTF exporter then writes both shells: nothing in
+`bpy.ops.export_scene.gltf` welds coincident vertices, so the file
+carries twice the triangles of the visible solid.
+
+**Who hits this:** kit-bash and boolean-cleanup pipelines, duplicated
+objects joined back onto themselves, and generators that emit a part
+twice. The asset looks like one cube in Blender and in the engine: the
+two shells are identical triangles, so the depth test hides the second
+without flicker. The cost is invisible in the viewport and real on disk
+and at runtime: double the draw triangles, a collider built from the mesh
+twice as heavy, and overlapping lightmap UVs if the shells were unwrapped.
+
+**What catches it:** a coincident-vertex check, not a manifold check.
+`bmesh.ops.find_doubles(dist=1e-5)` reports **8** doubles on this mesh
+while the non-manifold count stays **0**. That is why the showcase
+hygiene budgets count doubles separately from non-manifold edges. The
+fix is `bmesh.ops.remove_doubles` before export.
+
+## What the check asserts
 
 **Pre-assertion (pathology exists):** **16** verts, **8** unique
-positions, **12** faces, **24** edges, valence all 2. `--no-duplicate`
-exits 3.
+positions, **12** faces, **24** edges, valence 2 on every edge.
+`--no-duplicate` builds a single cube and exits 3. Vert count 16 alone is
+not enough, since any 16-vert mesh has it. Unique positions = 8 is the
+construction witness.
+
+**Handling (second axis):** read back from the written `.gltf` and its
+`.bin`: **48** loop-split positions, **24** triangles, **8** unique
+positions. `--weld` runs `remove_doubles` after the pre-assertion, the
+file then carries 24 positions and 12 triangles, and the check exits 4.
+
+`remove_doubles` collapses the pair to one cube: 8 verts, 12 edges,
+6 faces, valence 2. That is identical in every count to a cube built
+once. It does not leave a 4-faces-per-edge mesh.
+
+## Versions
+
+Re-verified on Blender 4.5.11 LTS, 5.1.2 and 5.2.1 LTS. Every count
+above is the same on all three, including the `find_doubles` and
+non-manifold figures and both falsifier exits. Not a version split.
 
-**Handling (second axis):** glTF ships **48** loop-split positions,
-**24** tris, **8** unique. Vert count 16 is not enough; unique=8 is
-the construction axis; 24 tris vs 12 after `remove_doubles` is the
-export axis. `--weld` after the pre-assert exits 4.
+No gallery still. Two coincident cubes look like one cube; the defect
+is only in the counts.
 
-`remove_doubles` collapses to one cube (8/12/6), still manifold — not
-a 4-face-per-edge mesh. Same on 4.5 LTS and 5.2 LTS.
+## API reference
 
-No gallery still. Two coincident cubes look like one cube.
+- [`bmesh.ops.find_doubles`](https://docs.blender.org/api/current/bmesh.ops.html#bmesh.ops.find_doubles)
+  and [`bmesh.ops.remove_doubles`](https://docs.blender.org/api/current/bmesh.ops.html#bmesh.ops.remove_doubles)
+  ([4.5 LTS](https://docs.blender.org/api/4.5/bmesh.ops.html#bmesh.ops.remove_doubles))
+- [`bpy.ops.export_scene.gltf`](https://docs.blender.org/api/current/bpy.ops.export_scene.html#bpy.ops.export_scene.gltf)
+  ([4.5 LTS](https://docs.blender.org/api/4.5/bpy.ops.export_scene.html#bpy.ops.export_scene.gltf))
 
 ## Run
 
diff --git a/examples/gallery.json b/examples/gallery.json
index 40322804..fa5b2a2a 100644
--- a/examples/gallery.json
+++ b/examples/gallery.json
@@ -658,7 +658,7 @@
       "name": "gn-zone-iterate",
       "dir": "examples/gn-zone-iterate",
       "teaches": "Repeat Zone and For Each Element only iterate after pair_with_output. Evaluated cube counts follow 8 times (1+N) and 8 times P, not tree structure.",
-      "alt": "Four ochre cubes in a row from a Repeat zone beside a vertical stack of six cyan cubes from a For Each zone.",
+      "alt": "Four brass cubes evenly spaced in a row from a Repeat zone beside a vertical stack of six cyan cubes from a For Each zone.",
       "witnessesFix": "Repeat 32/24 verts/faces with X-centers at k*1.2; For Each 48/36 with Z-centers at i*0.6+0.21. Unpaired evaluates empty; For Each main Geometry passthrough is 6 verts.",
       "hero": "docs/gallery/assets/gn-zone-iterate-hero.webp",
       "preview": "examples/gn-zone-iterate/preview.webp",
diff --git a/examples/gn-zone-iterate/gn_zone_iterate.py b/examples/gn-zone-iterate/gn_zone_iterate.py
index fd7cea44..c75160d1 100644
--- a/examples/gn-zone-iterate/gn_zone_iterate.py
+++ b/examples/gn-zone-iterate/gn_zone_iterate.py
@@ -298,6 +298,19 @@ def eevee_engine_id():
     return "BLENDER_EEVEE" if bpy.app.version >= (5, 0, 0) else "BLENDER_EEVEE_NEXT"
 
 
+def _node_materials(ob):
+    """Materials the object's Geometry Nodes tree assigns (Set Material nodes)."""
+    out = []
+    for md in ob.modifiers:
+        if md.type == "NODES" and md.node_group is not None:
+            for node in md.node_group.nodes:
+                if node.bl_idname == "GeometryNodeSetMaterial":
+                    mat = node.inputs["Material"].default_value
+                    if mat is not None and mat not in out:
+                        out.append(mat)
+    return out
+
+
 def render_still(rpt, fee, path, engine):
     scene = bpy.context.scene
 
@@ -337,16 +350,32 @@ def light(name, loc, energy, size, col, rot):
     light("Key", (-4.0, -5.0, 6.0), 520.0, 5.0, (1.0, 0.96, 0.9), (46, 0, -35))
     light("Fill", (5.0, -3.5, 3.0), 160.0, 9.0, (0.75, 0.85, 1.0), (62, 0, 50))
     light("Wedge", (2.5, 5.5, 4.0), 360.0, 6.0, (1.0, 0.76, 0.5), (-68, 0, 190))
-    light("Glint", (0.4, -5.2, 5.5), 700.0, 0.9, (1.0, 0.92, 0.75), (42, 0, 8))
-
+    # Broad, not a 0.9 m spot: the small Glint blew the top tower cube out
+    # to near-white cyan, the brightest thing in frame by a wide margin.
+    light("Glint", (0.4, -5.2, 5.5), 300.0, 3.0, (1.0, 0.92, 0.75), (42, 0, 8))
+    # Rim from behind so the cube silhouettes separate from the dark wall.
+    light("Rim", (-1.0, 4.5, 4.5), 260.0, 4.0, (0.70, 0.82, 1.0), (-50, 0, 180))
+
+    # Presentation only: the check never reads materials. 0.85 metallic in a
+    # near-black world reflected near-black, and the brass read as mustard
+    # card. Less metal and a warmer, brighter base let the key shape it.
+    for ob, rough, metal in ((rpt, 0.42, 0.55), (fee, 0.38, 0.10)):
+        for mat in _node_materials(ob):
+            bsdf = mat.node_tree.nodes.get("Principled BSDF")
+            if bsdf is not None:
+                bsdf.inputs["Metallic"].default_value = metal
+                bsdf.inputs["Roughness"].default_value = rough
+
+    # Centred on the pair and more frontal: from (6.6, -9.3) the repeat row
+    # foreshortened into a diagonal and the tower hugged the right edge.
     aim = bpy.data.objects.new("Aim", None)
-    aim.location = (0.0, 0.0, 1.50)
+    aim.location = (-0.10, 0.0, 1.62)
     aim.hide_render = True
     scene.collection.objects.link(aim)
     cam_data = bpy.data.cameras.new("Cam")
     cam_data.lens = 50.0
     cam = bpy.data.objects.new("Cam", cam_data)
-    cam.location = (6.6, -9.3, 3.55)
+    cam.location = (2.7, -10.6, 3.1)
     scene.collection.objects.link(cam)
     scene.camera = cam
     track = cam.constraints.new("TRACK_TO")
diff --git a/examples/gn-zone-iterate/preview.webp b/examples/gn-zone-iterate/preview.webp
index 459b37b2..25b04f98 100644
Binary files a/examples/gn-zone-iterate/preview.webp and b/examples/gn-zone-iterate/preview.webp differ
diff --git a/showcase/README.md b/showcase/README.md
index 1b489db6..9236857a 100644
--- a/showcase/README.md
+++ b/showcase/README.md
@@ -51,6 +51,7 @@ entry in `showcase/gallery.json`, and a rendered still.
   (exit 19). `--float-rivets` lifts fasteners off their host (exit 18).
   `--round-haft` turns an oval section round (exit 19).
   `--float-nails` lifts nail heads off their strap (exit 18).
+  `--short-mortar` stops every mortar joint shy of its stones (exit 18).
   `--sharp-iron` skips a chamfer pass so the edge-treatment budget fails
   (file-local code; `crate-stack` uses 21).
   A budget with no falsifier witnesses nothing:
@@ -324,6 +325,26 @@ entry in `showcase/gallery.json`, and a rendered still.
   threshold taken from the plate (`IRON_WRAP * 0.5`), not from the
   fastener: a yawed 10 mm head has a world AABB wider than 10 mm, and a
   fixed 10 mm threshold silently dropped 8 of 48 nails.
+- **A joint is filled, not open (exit 18).** Masonry, brick and
+  stacked-stone pieces separate their blocks with a named joint, and a
+  joint left as air is a stack of floating blocks with daylight through
+  every course. `stone-archway` shipped that way: 7 mm bed joints and
+  9.7 mm voussoir joints, none of them touching. Fill each joint with its
+  own mortar shell, sized from the two blocks it sits between, recessed
+  behind their faces by more than the chamfer so it reads as a raked
+  joint, and biting a named depth into both. Assert every mortar shell
+  BVH-overlaps **exactly two** stones — one means a bed left hanging,
+  none means the air gap came back. Keep the mortar shells out of any
+  classifier that names stone parts; left in, a bed classifies as a
+  course and every downstream stone budget measures the wrong
+  neighbour. Add mortar after the chamfer pass, unchamfered: a 6 mm
+  chamfer on a 10 mm bed eats it.
+- **Stone is not noise stretched over a block.** A noise-driven colour
+  mix sampled so its features streak read as wood grain on
+  `stone-archway` at hero scale. Stone wants isotropic object-space
+  mottling, fine speckle driving roughness and a small bump, and a
+  seeded tone per block as a face attribute so no two stones match.
+  Chain a baked normal map *under* that bump rather than replacing it.
 - **Identical boards read as CG.** Planks cut from one material are one
   plank repeated. Give each shell a seeded tone and its own grain
   direction — its long axis, recovered from its vertices — as face
diff --git a/showcase/gallery.json b/showcase/gallery.json
index 35931843..402aebeb 100644
--- a/showcase/gallery.json
+++ b/showcase/gallery.json
@@ -365,7 +365,7 @@
       "name": "stone-archway",
       "dir": "showcase/stone-archway",
       "teaches": "A procedural masonry archway — coursed piers, projecting imposts, nine voussoirs and a proud keystone — carried through UVs, bake, LOD, collider, and Unity glTF, asserting recomputed budgets rather than an API contract.",
-      "alt": "A freestanding stone archway of coursed piers and a semicircular arch with a keystone.",
+      "alt": "A freestanding grey stone archway of coursed piers and a semicircular arch with a keystone, laid in pale recessed mortar joints.",
       "witnessesFix": "Recomputed: 924 tris, two materials with 182 dressed and 364 ashlar faces re-stamped after the chamfer, UVs in 0..1 with zero AABB overlap, outer AABB 1.644×0.510×2.057 m, clear opening 1.203 m, zmin 0, hygiene 0 including zero coplanar disjoint pairs, both piers grounded, the springing joint an overlap, all eight mortar joints at 9.70 mm inside the 6–17 mm band, and every intrados vertex within 0.97 mm of the declared 0.60 m radius over 178°. --off-circle exits 19 on the circle fit; --wide-mortar exits 18 on the joint band.",
       "hero": "docs/gallery/assets/stone-archway-hero.webp",
       "preview": "showcase/stone-archway/preview.webp",
diff --git a/showcase/stone-archway/README.md b/showcase/stone-archway/README.md
index 0639ded2..4ee947fc 100644
--- a/showcase/stone-archway/README.md
+++ b/showcase/stone-archway/README.md
@@ -1,9 +1,10 @@
 # stone-archway
 
-![A semicircular masonry archway: coursed piers, projecting imposts, nine voussoirs and a proud keystone](preview.webp)
+![A semicircular masonry archway: coursed piers, projecting imposts, nine voussoirs and a proud keystone, laid in recessed mortar joints](preview.webp)
 
 A freestanding masonry arch — two coursed piers, projecting imposts, nine
-voussoirs turning a semicircle, and a keystone standing proud at the crown.
+voussoirs turning a semicircle, and a keystone standing proud at the crown,
+every joint filled with a recessed mortar bed.
 **A showcase piece, not an example** — it witnesses no API contract. It
 asserts that generated geometry meets declared asset budgets, recomputed
 from the finished mesh.
@@ -13,7 +14,7 @@ from the finished mesh.
 | Shipped content | Used for |
 | --- | --- |
 | `skills/mesh-editing-and-bmesh` | wedge and box construction, chamfer, UVs in one `bmesh` |
-| `skills/procedural-materials-and-shaders` | two Principled stone materials with noise-driven weathering |
+| `skills/procedural-materials-and-shaders` | ashlar, dressed stone and mortar: object-space mottling, speckle, bump, per-block tone |
 | `skills/bake-high-to-low` | Cycles tangent-space normal bake, high onto low |
 | `skills/engine-export-presets` | Unity glTF (`export_yup=True`) |
 | `skills/depsgraph-and-evaluated-data` | evaluated triangle counts for the LOD ratios |
@@ -53,19 +54,20 @@ the end.
 
 | Budget | Band | Measured |
 | --- | --- | --- |
-| Base triangles | 700–2600 | 924 |
+| Base triangles | 950–1450 | 1140 |
 | LOD1 ratio | 0.32–0.62 | 0.5000 |
-| LOD2 ratio | 0.10–0.35 | 0.2121 (5.2) / 0.2186 (4.5, 5.1) |
-| Material slots | exactly 2, distinct | 2 |
+| LOD2 ratio | 0.10–0.35 | 0.2140 (5.2) / 0.2193 (4.5, 5.1) |
+| Material slots | exactly 3, distinct | 3 |
 | Dressed faces (keystone, imposts, plinth and head courses) | ≥ 100 | 182 |
 | Ashlar faces | ≥ 280 | 364 |
-| UV bounds | inside 0..1 | (0.0017, 0.0017)–(0.9983, 0.9983) |
+| Mortar faces | ≥ 100 | 108 |
+| UV bounds | inside 0..1 | (0.0015, 0.0015)–(0.9985, 0.9985) |
 | UV AABB overlap | ≤ 1e-5 | 0.000000 |
 | Outer AABB | 1.644 × 0.510 × 2.057 m ± 0.020 | 1.6440 × 0.5100 × 2.0568 |
 | Clear opening | 1.200 m ± 0.015, measured between the pier faces | 1.2033 |
 | Collider triangles | ≤ 260 | 168 |
 | Normal bake | `{'FINISHED'}` with image data | `{'FINISHED'}`, `has_data=True` |
-| glTF export | file written, non-empty | ~87 kB |
+| glTF export | file written, non-empty | ~100 kB |
 | Hygiene | all zero | loose 0/0, non-manifold 0, zero-area 0, doubles 0, n-gons 0, coplanar disjoint pairs 0 |
 | Grounded AABB | \|zmin\| ≤ 1e-4 | 0.00000 |
 | Pier supports | 2 piers, each base course zmin ≤ 1e-3 | 2 at 0.00000 |
@@ -74,21 +76,54 @@ the end.
 | Mortar joints | every adjacent pair in 0.006–0.017 m | all eight at 0.00970 |
 | Intrados circle fit | every vertex within 0.004 m of R = 0.60 | 0.00097 |
 | Intrados arc span | ≥ 168° | 178.0° |
+| Mortar contact | 18 joints, each overlapping exactly 2 stones | 18, all 2 |
 
 Real-world size: a 1.20 m clear opening under a semicircular head, 1.64 m
 across the piers and 2.06 m to the top of the keystone — a garden gate arch.
 
+## Mortar
+
+Every joint used to be air. The pier courses stood 7 mm apart and the
+voussoirs 9.7 mm apart, none of them touching: each pier was a stack of
+floating blocks, with daylight through every joint in the ground-contact
+and joint close-ups. The mortar-band budget measured the gaps and passed,
+because the gaps were the right width. Nothing asked what was in them.
+
+Each joint now holds a mortar shell sized from the two blocks it sits
+between (`add_mortar`): beds between courses and under each impost, and
+wedges between voussoirs. Each is recessed `MORTAR_RECESS` (chamfer plus
+3 mm) behind the stone faces, so it reads as a raked joint, and bites
+`MORTAR_BITE` (1.5 mm) into both blocks. Mortar is added after the
+chamfer pass and left unchamfered, and `classify` skips mortar shells, so
+every stone budget — circle fit, joint band, keystone, supports — still
+measures stone against stone.
+
+`mortar_audit` asserts that each of the 18 mortar shells BVH-overlaps
+exactly two stones. `--short-mortar` stops every joint 1 mm shy of both
+blocks, so each shell touches none, and the piece exits 18.
+
+## Surface
+
+The stone used to read as wood. Its noise-driven colour mix streaked at
+hero scale into long brown grain, and under neutral light it looked like
+cream plaster. `stone_material` now samples object space with isotropic
+noise: mottling for colour, fine speckle driving roughness, and a small
+bump for pitting. A seeded `BlockTone` face attribute (`paint_blocks`)
+shades each stone differently. Dressed stone is paler and smoother than
+ashlar; mortar is a flat grey-beige. The baked normal map is chained
+under the bump (`wire_normal`) rather than replacing it.
+
 ## Determinism
 
 Fixed seed 23; no unseeded randomness. Every measured value above is
 byte-identical on 4.5.11, 5.1.2 and 5.2.1 **except** LOD2, where
-`DECIMATE COLLAPSE` produces 196 triangles on 5.2 and 202 on 4.5 and 5.1.
-That is why the LOD gate is a ratio band (0.10–0.35, measured 0.2121 and
-0.2186) and not an exact count.
+`DECIMATE COLLAPSE` produces 244 triangles on 5.2 and 250 on 4.5 and 5.1.
+That is why the LOD gate is a ratio band (0.10–0.35, measured 0.2140 and
+0.2193) and not an exact count.
 
 ## Falsifiers
 
-Each breaks one pipeline stage so a **named** budget fails. All seven were
+Each breaks one pipeline stage so a **named** budget fails. All eight were
 run on 4.5.11, 5.1.2 and 5.2.1 and produced the same exit code on all three.
 
 | Flag | Breaks | Exit |
@@ -100,6 +135,7 @@ run on 4.5.11, 5.1.2 and 5.2.1 and produced the same exit code on all three.
 | `--sink-keystone` | sinks the keystone to a quarter of its projection (8.75 mm) — the imposts still set the Y envelope, so the bounding box is unchanged | 17 |
 | `--wide-mortar` | triples the joint angle, opening every joint to 29.1 mm | 18 |
 | `--off-circle` | wanders the intrados radius ±18 mm while keeping angles, joints and envelope | 19 |
+| `--short-mortar` | stops every mortar joint 1 mm shy of both stones; each of the 18 touches none, mortar-contact budget | 18 |
 
 Three of these needed the model changed, not the budget:
 
@@ -162,13 +198,13 @@ against it. `1` is the FATAL wrapper — a crash, never a named check.
 | 15 | Mesh hygiene (`--stray-vert`) |
 | 16 | Grounded zmin, or a pier base floating (`--lift-z`, `--float-pier`) |
 | 17 | Keystone projection or springing joint (`--sink-keystone`) |
-| 18 | Mortar joint outside band (`--wide-mortar`) |
+| 18 | Mortar joint outside band (`--wide-mortar`), or a mortar shell not seated in exactly two stones (`--short-mortar`) |
 | 19 | Intrados circle fit, or clear opening (`--off-circle`) |
 
 ## Run it
 
 ```bash
-# Budget check, no render. ~0.82 s on 4.5, ~0.85 s on 5.1, ~0.98 s on 5.2.
+# Budget check, no render. ~1.1 s on 4.5, ~1.2 s on 5.1, ~1.4 s on 5.2.
 blender --background --python stone_archway.py --
 
 # Falsifier: the intrados stops being a circle. Must exit 19.
@@ -187,12 +223,13 @@ Smoke runs the check-only path. It does not pass `--output` or any falsifier.
 
 | Value | 4.5.11 | 5.1.2 | 5.2.1 |
 | --- | --- | --- | --- |
-| Base triangles | 924 | 924 | 924 |
-| LOD1 tris / ratio | 462 / 0.5000 | 462 / 0.5000 | 462 / 0.5000 |
-| LOD2 tris / ratio | 202 / 0.2186 | 202 / 0.2186 | 196 / 0.2121 |
-| Face counts (ashlar / dressed) | 364 / 182 | 364 / 182 | 364 / 182 |
+| Base triangles | 1140 | 1140 | 1140 |
+| LOD1 tris / ratio | 570 / 0.5000 | 570 / 0.5000 | 570 / 0.5000 |
+| LOD2 tris / ratio | 250 / 0.2193 | 250 / 0.2193 | 244 / 0.2140 |
+| Face counts (ashlar / dressed / mortar) | 364 / 182 / 108 | same | same |
 | Outer AABB | 1.6440 × 0.5100 × 2.0568 | same | same |
 | Collider tris | 168 | 168 | 168 |
 | Intrados deviation | 0.00097 | 0.00097 | 0.00097 |
 | Mortar joints | all 0.00970 | all 0.00970 | all 0.00970 |
-| Check wall-clock | ~0.82 s | ~0.85 s | ~0.98 s |
+| Mortar contact | 18 × 2 stones | same | same |
+| Check wall-clock | ~1.11 s | ~1.18 s | ~1.37 s |
diff --git a/showcase/stone-archway/preview.webp b/showcase/stone-archway/preview.webp
index dbb481b1..6a0b76df 100644
Binary files a/showcase/stone-archway/preview.webp and b/showcase/stone-archway/preview.webp differ
diff --git a/showcase/stone-archway/stone_archway.py b/showcase/stone-archway/stone_archway.py
index 663ca1f8..d8a8f237 100644
--- a/showcase/stone-archway/stone_archway.py
+++ b/showcase/stone-archway/stone_archway.py
@@ -2,7 +2,7 @@
 
 Asserts budget conformance of a procedural masonry arch: two coursed
 piers, nine voussoirs turning a semicircle, and a proud keystone, carried
-through UVs, two materials, a high-to-low normal bake, an LOD chain, a
+through UVs, three materials (ashlar, dressed stone, mortar), a high-to-low normal bake, an LOD chain, a
 convex collider, and a Unity glTF export.
 
 The budget that matters here is the one an arch can fail invisibly: the
@@ -16,7 +16,8 @@
 budget: ``--skip-decimate`` the LOD-ratio band, ``--stray-vert`` mesh
 hygiene, ``--lift-z`` grounded zmin, ``--float-pier`` the named pier
 supports, ``--sink-keystone`` the keystone joint, ``--wide-mortar`` the
-mortar-joint band, ``--off-circle`` the intrados circle fit.
+mortar-joint band, ``--off-circle`` the intrados circle fit,
+``--short-mortar`` the mortar-contact budget.
 
 Fixed seed 23 for course and block weathering. DECIMATE COLLAPSE
 triangle counts are not byte-identical across Blender versions — the LOD
@@ -87,15 +88,15 @@
 SPAN_TOL = 0.015
 OPENING_W = 2.0 * R_IN
 
-BASE_TRIS_MIN = 700
-BASE_TRIS_MAX = 2600
+BASE_TRIS_MIN = 950
+BASE_TRIS_MAX = 1450
 LOD1_RATIO_MIN = 0.32
 LOD1_RATIO_MAX = 0.62
 LOD2_RATIO_MIN = 0.10
 LOD2_RATIO_MAX = 0.35
 LOD1_TARGET = 0.50
 LOD2_TARGET = 0.22
-MATERIAL_COUNT = 2
+MATERIAL_COUNT = 3
 UV_EPS = 1e-4
 UV_OVERLAP_MAX = 1e-5
 COLLIDER_TRIS_MAX = 260
@@ -123,6 +124,19 @@
 
 ASHLAR_IDX = 0
 DRESSED_IDX = 1
+MORTAR_IDX = 2
+
+# Mortar fills every joint. Each bed or wedge is built from the two blocks
+# it sits between: recessed behind their faces (deeper than the chamfer, so
+# it reads as a raked joint rather than a filled one) and biting into both.
+# Without it every course floated on 7 mm of air and daylight showed
+# through each joint.
+MORTAR_RECESS = CHAMFER + 0.003
+MORTAR_BITE = 0.0015
+SHORT_MORTAR_CLEAR = 0.001
+N_MORTAR = 2 * N_COURSE + (N_VOUSSOIR - 1)
+MORTAR_FACES_MIN = 100
+BLOCK_TONE_JITTER = 0.25
 
 
 def eevee_engine_id():
@@ -280,6 +294,9 @@ def build_pier(bm, sign, rng, float_pier=False):
     heights = [usable * r / total for r in raw]
     verts = []
     blocks = []
+    # (width, depth, zmin, zmax) per block, bottom up, impost last: what
+    # the mortar beds between them are sized from.
+    stack = []
     z = FLOAT_PIER_LIFT if (float_pier and sign < 0) else 0.0
     for i, h in enumerate(heights):
         # Courses weather back a little as they rise; the jitter also keeps
@@ -295,6 +312,7 @@ def build_pier(bm, sign, rng, float_pier=False):
         )
         verts.extend(vs)
         blocks.append(block)
+        stack.append((T_V - inset, depth, z, z + h))
         z += h + COURSE_MORTAR
     # The impost rides on the courses rather than sitting at an absolute
     # height: pinned to H_SPRING it stays put while --float-pier lifts the
@@ -307,7 +325,8 @@ def build_pier(bm, sign, rng, float_pier=False):
     )
     verts.extend(vs)
     blocks.append(block)
-    return verts, blocks
+    stack.append((T_V + 2.0 * IMPOST_OUT, WALL_Y + 2.0 * IMPOST_PROUD, z, z + IMPOST_H))
+    return verts, blocks, stack
 
 
 def build_arch(bm, rng, off_circle=False, sink_keystone=False, wide_mortar=False):
@@ -317,6 +336,7 @@ def build_arch(bm, rng, off_circle=False, sink_keystone=False, wide_mortar=False
     cz = H_SPRING - SPRING_BITE
     verts = []
     blocks = []
+    wedges = []
     for k in range(N_VOUSSOIR):
         is_key = k == KEY_INDEX
         widen = KEY_WIDEN if is_key else 0.0
@@ -342,7 +362,43 @@ def build_arch(bm, rng, off_circle=False, sink_keystone=False, wide_mortar=False
         vs, block = add_wedge(bm, cz, a0, a1, r0, r1, hy, mat)
         verts.extend(vs)
         blocks.append(block)
-    return verts, blocks
+        wedges.append((a0, a1, r0, r1, hy))
+    return verts, blocks, wedges
+
+
+def add_mortar(bm, sign, stack, wedges, short=False):
+    """Beds between pier courses and wedges between voussoirs.
+
+    Every dimension comes from the two blocks the joint sits between, so a
+    course that weathers back or a voussoir that rises takes its mortar with
+    it. ``short`` stops each joint SHORT_MORTAR_CLEAR shy of both blocks —
+    the falsifier for the mortar-contact budget.
+    """
+    bite = -SHORT_MORTAR_CLEAR if short else MORTAR_BITE
+    if stack is not None:
+        x = sign * (R_IN + T_V / 2.0)
+        for (w0, d0, _z0, top), (w1, d1, bot, _z1) in zip(stack, stack[1:]):
+            h = (bot - top) + 2.0 * bite
+            add_box(
+                bm,
+                (x, 0.0, 0.5 * (top + bot)),
+                (min(w0, w1) - 2.0 * MORTAR_RECESS,
+                 min(d0, d1) - 2.0 * MORTAR_RECESS, h),
+                MORTAR_IDX,
+            )
+    if wedges is not None:
+        cz = H_SPRING - SPRING_BITE
+        for (_a0, a1, r0a, r1a, hya), (b0, _b1, r0b, r1b, hyb) in zip(wedges, wedges[1:]):
+            ri = max(r0a, r0b) + MORTAR_RECESS
+            # Angular bite taken at the inner radius, so it is never less
+            # than MORTAR_BITE anywhere along the joint.
+            da = bite / ri
+            add_wedge(
+                bm, cz, a1 - da, b0 + da, ri,
+                min(r1a, r1b) - MORTAR_RECESS,
+                min(hya, hyb) - MORTAR_RECESS,
+                MORTAR_IDX,
+            )
 
 
 def build_arch_mesh(
@@ -351,15 +407,18 @@ def build_arch_mesh(
     sink_keystone=False,
     wide_mortar=False,
     float_pier=False,
+    short_mortar=False,
 ):
     rng = random.Random(ARCH_SEED)
     bm = bmesh.new()
     try:
         blocks = []
+        stacks = []
         for sign in (-1.0, 1.0):
-            _v, bl = build_pier(bm, sign, rng, float_pier=float_pier)
+            _v, bl, st = build_pier(bm, sign, rng, float_pier=float_pier)
             blocks.extend(bl)
-        _v, bl = build_arch(
+            stacks.append((sign, st))
+        _v, bl, wedges = build_arch(
             bm,
             rng,
             off_circle=off_circle,
@@ -379,6 +438,12 @@ def build_arch_mesh(
                 clamp_overlap=True,
             )
         assign_materials_by_block(bm, blocks)
+        # Mortar after the chamfer: it sits recessed behind the stone and a
+        # chamfer on a 10 mm bed would eat it. It also stays out of the
+        # block re-stamp, which only knows stone.
+        for sign, st in stacks:
+            add_mortar(bm, sign, st, None, short=short_mortar)
+        add_mortar(bm, 0.0, None, wedges, short=short_mortar)
         pack_uvs(bm)
         bmesh.ops.recalc_face_normals(bm, faces=list(bm.faces))
         for face in bm.faces:
@@ -388,44 +453,123 @@ def build_arch_mesh(
         me.update()
     finally:
         bm.free()
+    paint_blocks(me)
     obj = bpy.data.objects.new(name, me)
     bpy.context.collection.objects.link(obj)
     return obj
 
 
-def principled(name, color, metallic, roughness, noise_scale=0.0, wear=None):
+def paint_blocks(me):
+    """A seeded tone per stone, as the ``BlockTone`` face attribute.
+
+    Nineteen blocks out of one material are one block repeated; a quarried
+    arch has every stone a shade apart. Mortar keeps the neutral 0.5.
+    """
+    tone = [0.5] * len(me.polygons)
+    mortar = mortar_verts(me)
+    owner = {}
+    rng = random.Random(ARCH_SEED * 17)
+    for g in shells(me):
+        t = 0.5 if g[0] in mortar else 0.5 + rng.uniform(-BLOCK_TONE_JITTER, BLOCK_TONE_JITTER)
+        for i in g:
+            owner[i] = t
+    for p in me.polygons:
+        tone[p.index] = owner[p.vertices[0]]
+    attr = me.attributes.new("BlockTone", "FLOAT", "FACE")
+    attr.data.foreach_set("value", tone)
+
+
+def _sock(sockets, identifier):
+    """A Mix-node socket by identifier; its A/B/Result names repeat per type."""
+    return next(sk for sk in sockets if sk.identifier == identifier)
+
+
+def stone_material(name, light, dark, roughness, mottle, speck, bump):
+    """Stone, not timber: isotropic mottling, fine speckle and pitting.
+
+    The old noise-driven mix read as long brown streaks at hero scale, and
+    the ashlar looked like wood grain. Everything here samples object space
+    with isotropic noise, so nothing in the pattern has a direction.
+    """
     mat = bpy.data.materials.new(name)
     mat.use_nodes = True
     nt = mat.node_tree
     bsdf = nt.nodes["Principled BSDF"]
-    bsdf.inputs["Base Color"].default_value = color
-    bsdf.inputs["Metallic"].default_value = metallic
-    bsdf.inputs["Roughness"].default_value = roughness
-    if noise_scale > 0.0 and wear is not None:
-        tex = nt.nodes.new("ShaderNodeTexNoise")
-        tex.inputs["Scale"].default_value = noise_scale
-        tex.inputs["Detail"].default_value = 9.0
-        tex.inputs["Roughness"].default_value = 0.6
-        mix = nt.nodes.new("ShaderNodeMix")
-        mix.data_type = "RGBA"
-        mix.inputs["A"].default_value = color
-        mix.inputs["B"].default_value = wear
-        fac = mix.inputs.get("Factor") or mix.inputs.get("Fac")
-        nt.links.new(tex.outputs["Fac"], fac)
-        nt.links.new(mix.outputs["Result"], bsdf.inputs["Base Color"])
-        rmix = nt.nodes.new("ShaderNodeMix")
-        rmix.data_type = "FLOAT"
-        rmix.inputs["A"].default_value = roughness
-        rmix.inputs["B"].default_value = min(1.0, roughness + 0.16)
-        rfac = rmix.inputs.get("Factor") or rmix.inputs.get("Fac")
-        nt.links.new(tex.outputs["Fac"], rfac)
-        nt.links.new(rmix.outputs["Result"], bsdf.inputs["Roughness"])
+    coord = nt.nodes.new("ShaderNodeTexCoord")
+    mot = nt.nodes.new("ShaderNodeTexNoise")
+    mot.inputs["Scale"].default_value = mottle
+    mot.inputs["Detail"].default_value = 4.0
+    mot.inputs["Roughness"].default_value = 0.55
+    nt.links.new(coord.outputs["Object"], mot.inputs["Vector"])
+    ramp = nt.nodes.new("ShaderNodeValToRGB")
+    ramp.color_ramp.elements[0].position = 0.32
+    ramp.color_ramp.elements[0].color = dark
+    ramp.color_ramp.elements[1].position = 0.70
+    ramp.color_ramp.elements[1].color = light
+    nt.links.new(mot.outputs["Fac"], ramp.inputs["Fac"])
+    spk = nt.nodes.new("ShaderNodeTexNoise")
+    spk.inputs["Scale"].default_value = speck
+    spk.inputs["Detail"].default_value = 2.0
+    nt.links.new(coord.outputs["Object"], spk.inputs["Vector"])
+    gain = nt.nodes.new("ShaderNodeMapRange")
+    gain.inputs["To Min"].default_value = 0.82
+    gain.inputs["To Max"].default_value = 1.12
+    nt.links.new(spk.outputs["Fac"], gain.inputs["Value"])
+    mix = nt.nodes.new("ShaderNodeMix")
+    mix.data_type = "RGBA"
+    mix.blend_type = "MULTIPLY"
+    _sock(mix.inputs, "Factor_Float").default_value = 1.0
+    nt.links.new(ramp.outputs["Color"], _sock(mix.inputs, "A_Color"))
+    nt.links.new(gain.outputs["Result"], _sock(mix.inputs, "B_Color"))
+    # Per-stone shade from the BlockTone face attribute (paint_blocks).
+    tone = nt.nodes.new("ShaderNodeAttribute")
+    tone.attribute_name = "BlockTone"
+    shade = nt.nodes.new("ShaderNodeMath")
+    shade.operation = "MULTIPLY_ADD"
+    shade.inputs[1].default_value = 0.8
+    shade.inputs[2].default_value = 0.6
+    nt.links.new(tone.outputs["Fac"], shade.inputs[0])
+    mix2 = nt.nodes.new("ShaderNodeMix")
+    mix2.data_type = "RGBA"
+    mix2.blend_type = "MULTIPLY"
+    _sock(mix2.inputs, "Factor_Float").default_value = 1.0
+    nt.links.new(_sock(mix.outputs, "Result_Color"), _sock(mix2.inputs, "A_Color"))
+    nt.links.new(shade.outputs["Value"], _sock(mix2.inputs, "B_Color"))
+    nt.links.new(_sock(mix2.outputs, "Result_Color"), bsdf.inputs["Base Color"])
+    rough = nt.nodes.new("ShaderNodeMapRange")
+    rough.inputs["To Min"].default_value = roughness - 0.06
+    rough.inputs["To Max"].default_value = min(1.0, roughness + 0.08)
+    nt.links.new(spk.outputs["Fac"], rough.inputs["Value"])
+    nt.links.new(rough.outputs["Result"], bsdf.inputs["Roughness"])
+    if bump > 0.0:
+        bmp = nt.nodes.new("ShaderNodeBump")
+        bmp.inputs["Strength"].default_value = bump
+        bmp.inputs["Distance"].default_value = 0.002
+        nt.links.new(spk.outputs["Fac"], bmp.inputs["Height"])
+        nt.links.new(bmp.outputs["Normal"], bsdf.inputs["Normal"])
     return mat
 
 
-def assign_slots(obj, ashlar, dressed):
+def arch_materials():
+    """(ashlar, dressed, mortar): shared by the check, the render and inspection."""
+    ashlar = stone_material(
+        "ArchAshlar", (0.40, 0.355, 0.285, 1.0), (0.235, 0.205, 0.160, 1.0),
+        0.86, mottle=5.0, speck=140.0, bump=0.30,
+    )
+    dressed = stone_material(
+        "ArchDressed", (0.56, 0.50, 0.405, 1.0), (0.40, 0.355, 0.285, 1.0),
+        0.66, mottle=3.0, speck=220.0, bump=0.12,
+    )
+    mortar = stone_material(
+        "ArchMortar", (0.50, 0.485, 0.450, 1.0), (0.40, 0.385, 0.355, 1.0),
+        0.95, mottle=12.0, speck=300.0, bump=0.0,
+    )
+    return ashlar, dressed, mortar
+
+
+def assign_slots(obj, ashlar, dressed, mortar):
     mats = obj.data.materials
-    for i, mat in enumerate((ashlar, dressed)):
+    for i, mat in enumerate((ashlar, dressed, mortar)):
         if i < len(mats):
             mats[i] = mat
         else:
@@ -621,10 +765,25 @@ def pair_gap(me, tree_a, group_b, tree_b=None):
     return best
 
 
+def mortar_verts(me):
+    """Vertices of mortar faces. Mortar is its own shells; stone budgets skip it."""
+    return {
+        i for p in me.polygons if p.material_index == MORTAR_IDX for i in p.vertices
+    }
+
+
 def classify(me):
-    """Name the shells: pier courses by side, voussoirs by crown angle."""
+    """Name the stone shells: pier courses by side, voussoirs by crown angle.
+
+    Mortar shells are skipped. Left in, a pier bed classifies as a course
+    and a voussoir wedge as a voussoir, and every stone budget after this
+    measures the wrong neighbours.
+    """
     out = {"left": [], "right": [], "voussoirs": []}
+    mortar = mortar_verts(me)
     for g in shells(me):
+        if g[0] in mortar:
+            continue
         pts = [me.vertices[i].co for i in g]
         zmin = min(p.z for p in pts)
         zmax = max(p.z for p in pts)
@@ -751,6 +910,31 @@ def arch_audit(me):
     }
 
 
+def mortar_audit(me):
+    """Every mortar shell must be seated in exactly two stones.
+
+    A joint that touches one stone is a bed left hanging; one that touches
+    none is the air gap the mortar exists to fill. Overlap is the metric:
+    each bed bites MORTAR_BITE into both blocks by construction, so the
+    BVH trees must intersect, and a bed that stops short of a block does
+    not.
+    """
+    mortar = mortar_verts(me)
+    stone_trees, mortar_trees = [], []
+    for g in shells(me):
+        if len(g) < 4:
+            continue
+        (mortar_trees if g[0] in mortar else stone_trees).append(shell_tree(me, g))
+    seats = []
+    for mt in mortar_trees:
+        seats.append(sum(1 for st in stone_trees if st is not None and mt.overlap(st)))
+    return {
+        "n": len(mortar_trees),
+        "seat_min": min(seats, default=0),
+        "seat_max": max(seats, default=0),
+    }
+
+
 def opening_audit(me):
     """Clear opening width at mid-pier height, measured from vertices."""
     # Band stops clear of the impost, which projects inboard of the pier
@@ -875,6 +1059,7 @@ def check(
     sink_keystone=False,
     wide_mortar=False,
     off_circle=False,
+    short_mortar=False,
 ):
     bpy.ops.wm.read_factory_settings(use_empty=True)
     flags = dict(
@@ -882,20 +1067,14 @@ def check(
         sink_keystone=sink_keystone,
         wide_mortar=wide_mortar,
         float_pier=float_pier,
+        short_mortar=short_mortar,
     )
     nothing = (None,) * 5
     low = build_arch_mesh("ArchLow", **flags)
     high = build_arch_mesh("ArchHigh", **flags)
-    ashlar = principled(
-        "ArchAshlar", (0.300, 0.219, 0.126, 1.0), 0.0, 0.80,
-        noise_scale=14.0, wear=(0.168, 0.113, 0.055, 1.0),
-    )
-    dressed = principled(
-        "ArchDressed", (0.452, 0.348, 0.205, 1.0), 0.0, 0.62,
-        noise_scale=8.0, wear=(0.262, 0.196, 0.108, 1.0),
-    )
-    assign_slots(low, ashlar, dressed)
-    assign_slots(high, ashlar, dressed)
+    ashlar, dressed, mortar = arch_materials()
+    assign_slots(low, ashlar, dressed, mortar)
+    assign_slots(high, ashlar, dressed, mortar)
     if stray_vert:
         add_stray_vert(low.data)
     if lift_z:
@@ -943,11 +1122,16 @@ def check(
         os.remove(export_path)
     export_unity(export_path, [low, collider])
     export_size = os.path.getsize(export_path) if os.path.isfile(export_path) else 0
+    # Blender points TMPDIR at its own temp preference, which on a portable
+    # build is the working directory, so the export must not outlive this.
+    if os.path.isfile(export_path):
+        os.remove(export_path)
 
     hyg = hygiene_audit(low.data)
     zf = zfight_pairs(low.data)
     ar = arch_audit(low.data)
     opening = opening_audit(low.data)
+    mo = mortar_audit(low.data)
 
     print(f"blender={tuple(bpy.app.version)} skip_decimate={skip_decimate}")
     print(f"measured mat_index_counts={idx_counts}")
@@ -979,6 +1163,9 @@ def check(
         f"key_proud={ar['key_proud']:.5f} spring_gap={ar['spring_gap']:.5f} "
         f"pier_worst={ar['pier_worst']:.5f} gaps={ar['gaps']}"
     )
+    print(
+        f"measured mortar n={mo['n']} seats=[{mo['seat_min']}, {mo['seat_max']}]"
+    )
 
     if not (BASE_TRIS_MIN <= base_tris <= BASE_TRIS_MAX):
         return (fail(
@@ -996,6 +1183,10 @@ def check(
         return (fail(
             f"ashlar faces {idx_counts.get(ASHLAR_IDX, 0)} < {ASHLAR_FACES_MIN}", 5
         ),) + nothing
+    if idx_counts.get(MORTAR_IDX, 0) < MORTAR_FACES_MIN:
+        return (fail(
+            f"mortar faces {idx_counts.get(MORTAR_IDX, 0)} < {MORTAR_FACES_MIN}", 5
+        ),) + nothing
     if u0 < -UV_EPS or v0 < -UV_EPS or u1 > 1.0 + UV_EPS or v1 > 1.0 + UV_EPS:
         return (fail(
             f"UVs outside 0..1: ({u0:.4f},{v0:.4f})-({u1:.4f},{v1:.4f})", 6
@@ -1058,6 +1249,12 @@ def check(
             f"mortar joints ({ar['gap_min']:.5f}, {ar['gap_max']:.5f}) outside "
             f"[{MORTAR_MIN}, {MORTAR_MAX}] (--wide-mortar is the designed fail)", 18
         ),) + nothing
+    if mo["n"] != N_MORTAR or mo["seat_min"] != 2 or mo["seat_max"] != 2:
+        return (fail(
+            f"mortar contact: {mo['n']} of {N_MORTAR} joints, stones seated per "
+            f"joint [{mo['seat_min']}, {mo['seat_max']}], need exactly 2 "
+            "(--short-mortar is the designed fail)", 18
+        ),) + nothing
     if ar["arc_dev"] > ARC_TOL or ar["arc_span"] < ARC_SPAN_MIN:
         return (fail(
             f"intrados off circle by {ar['arc_dev']:.5f} > {ARC_TOL} or spans "
@@ -1073,12 +1270,17 @@ def check(
 
 
 def wire_normal(mat, tex):
+    """Baked normal map into the BSDF, under the pitting bump if there is one."""
     nt = mat.node_tree
     bsdf = nt.nodes["Principled BSDF"]
     nrm = nt.nodes.new("ShaderNodeNormalMap")
     nrm.inputs["Strength"].default_value = 1.0
     nt.links.new(tex.outputs["Color"], nrm.inputs["Color"])
-    nt.links.new(nrm.outputs["Normal"], bsdf.inputs["Normal"])
+    bump = next((n for n in nt.nodes if n.bl_idname == "ShaderNodeBump"), None)
+    if bump is not None:
+        nt.links.new(nrm.outputs["Normal"], bump.inputs["Normal"])
+    else:
+        nt.links.new(nrm.outputs["Normal"], bsdf.inputs["Normal"])
 
 
 def render_still(low, ashlar, tex, path, engine):
@@ -1189,6 +1391,7 @@ def main():
     p.add_argument("--sink-keystone", action="store_true")
     p.add_argument("--wide-mortar", action="store_true")
     p.add_argument("--off-circle", action="store_true")
+    p.add_argument("--short-mortar", action="store_true")
     args = p.parse_args(argv)
 
     code, low, _high, ashlar, tex, _col = check(
@@ -1199,6 +1402,7 @@ def main():
         sink_keystone=args.sink_keystone,
         wide_mortar=args.wide_mortar,
         off_circle=args.off_circle,
+        short_mortar=args.short_mortar,
     )
     if code:
         return code