Sculpting (heads and characters, Blender 5.2)

Expert sculpting is structure first and surface last: masses blocked with stated planes and corners, proportions locked at low resolution, every stage judged by eye through a long lens, and appeal as the final test, not the mesh numbers. The agent builds blockout and primary forms headless (scripts/bx_sculpt.py: smooth-blend Clay, plane cuts, numpy brushes) and does client-quality surface work with Blender's real brushes in a live GUI session (bx_gui). If a sibling skill named here is missing from your available skills, ask the user to install it (npx skills add scenario-labs/skills --skill <name>); unattended, proceed from tool schemas and flag the gap.

REQUIRED BACKGROUND: scenario-blender-expert (execution channel, review loop, 5.2 API changes).

Stance (the expert delta)

• Planes are stated, not found. Thelen cuts plane borders with Draw Sharp and re-cuts them whenever a face "looks off"; Naydenov simplifies into planes, then smooths; Reinhardt uses Scrape, Trim and Line Project for clean cuts. Executable form: give the plane (point + normal) to Clay half-space clips or plane_cut / corner_cut. A flatten or scrape dab fits its plane to the ball under it, so it follows the ball.
• The jaw is a block with a gonial corner, the cheekbone a mass with its own lower plane. Zarins: the gonial angle is the age and sex dial, steep in adult males; the widest face point is the top of the zygomatic arch. Naydenov: the cheekbone runs from the ear down and forward, only its lower edge shows. Thelen: bone plus tissue, never razor sharp.
• Fix mass upstream; planes only restate. If re-cutting planes does not fix the look, the problem is mass or proportion (Thelen's diagnostic). Measured: plane cuts on a balloon jaw flipped the form metric but rendered as a gem facet; rebuilding the jaw block fixed it.
• Low resolution as long as possible. Abbitt: smoothing is strong only on big polygons; Thelen: lock proportions coarse. Symmetrize after every remesh (Keelan Jon), then a global relax (Kaspar FDscc66fC90 00:11:55).
• Indicate small landmarks early (nostrils, brows, eyes): Yan found a too-wide nose from the nostrils (vB7kPWjBgQI 00:05:11).
• Stylize by consistent exaggeration (Yan: pick it in minute one, make neighbors follow; a long face needs a smaller skull, not a stretch).
• A concept head needs its cues. Thelen: hair makes a male head read better (00:48:58); Naydenov: hair changes the read a lot (00:53:05). An "adventurer" with no hair or costume reads as a bald mannequin.
• Asymmetry and expression live on a shape key; the basis stays neutral and symmetric (Kaspar f-mx-Jfx9lA 00:09:44; Thelen 00:38:27). Expression tests expose proportion errors; fix them in the neutral (Kaspar 00:10:49).

Establish first

Input	Changes	Default when silent
Who (sex, age, type, attitude)	gonial angle, brow, jaw width, shape language	adult male, neutral basis, stated [added]
Style	stylized: exaggeration table; realistic: canon + reference	stylized, "abstracted enough to not be uncanny" (Kaspar)
Character cues	hair, costume, props that sell the type	at least hair plus one costume signifier [added]
Purpose	still (vertex paint, decimate) vs game or film (retopology)	still; scenario-blender-retopology if animated
Delivery framing	detail frequency, expression size	bust fills a 1080 px frame [added]
Scale	nothing if sizes are fractions of head height H	H = 0.24 m [added]
Channel	headless numpy / Clay, or live GUI brushes	headless blockout; GUI for surface when the bridge is up

Workflow

0. Design table. G = S.head_guides(H), a STYLE dict (the one or two exaggerations), the cue list, and the landmark points of the planes: gonion, chin bottom, cheekbone. GATE: written down.
1. Blockout (voxel H/40). Default for heads: Clay. Cranium ellipsoid clipped by skull side and front-taper half-spaces; a jaw sd_round_box BEHIND the mouth mound, clipped by side, underside and ramus planes through the gonion; a square chin block; cheekbone ellipsoids along the ear-to-cheek line with a lower plane; mouth mound; brow ridges; nose; neck leaning about 15 degrees; ears; frontal box around the eyes. Blend big masses at 0.08 to 0.15 H, clip edges at 0.02 to 0.03 H. Option: union_remesh of primitives (rounded_box is a Catmull-Clark blob that reads as a ball: never use it for a jaw). GATE: 1 component; lower_face_report(head, H)["ball"] False; silhouette plus 90 mm renders show a jawline and gonial corner in profile and three-quarter; the exaggeration visible.
2. Primary forms (H/100 to H/110). Rebuild the Clay at the finer voxel with landmarks: sockets (sphere 1.1 x eyeball, smaller than the lids), thin shell lids around separate eyeballs (Keelan Jon's lids from the eyeball, amVAlpxHp8k 00:37:05), nose wings tucked in, ear bowls, neck muscles. Hair and costume as separate Clay objects (to_object(name, symmetric=False) for anything asymmetric). GATE: profile beats; eyes not marbles or bags; hair frames the face; stage_report clean.
3. Secondary (H/130 to H/150, remesh_stage). Lines with crease_line (mouth, under-lip, lid rim) on surfaces facing the projection; nostrils from below. Restate planes with corner_cut / plane_cut only where the mass is right and moves stay small. GATE: under 100k faces (Abbitt), no scratches, cracks or rims in 90 mm renders.
4. Surface finish (client quality): live GUI. Real Clay Strips, Scrape, Crease Polish, Smooth 0.2 via bx_gui (fixed and verified: strokes raycast onto the mesh and pass object-space locations; set_view(frame=obj) first, view_distance a few head heights). Headless numpy strokes suit blockout and primary forms, not polish. Multires only on a settled clean base (Henning Cmi0KoFtc-4 00:16:04).
5. Expression. Neutral symmetric basis; sc = S.Sculptor(head, symmetry_x=False), move_feature the corner, cheek, lower lid, opposite brow; S.write_shape_key(head, "Smirk", sc.co). Size the corner move to the delivery framing (Numbers). Voxel remesh drops keys: last step.
6. Final render. S.final_render(objs, path, direction, lens=90, res=1600) (cavity, framed on real vertices) from front, profile, three-quarter, neutral and expression; open every image.

Inside every stage: render, name ONE weakest link, fix it, re-render (Yan). A metric that passes while the render looks wrong means the render wins.

Numbers

Value	Number	Source
Voxel ladder	H/40 blockout, H/65 to H/110 primary, H/130 to H/235 secondary, about H/330 detail	Morren, Abbitt; example
Faces from voxel	about 1.5 x area / voxel^2 (voxel_for_faces)	measured, 3 %
Example bust faces	H/40 8k, H/110 64k, H/150 103k (with neck)	measured
Face gates	shape before 100k; detail about 500k	Abbitt
Raw remesh mirror error	max 0.67 to 0.75 voxel, mean 0.05 to 0.07 voxel (nearest vertex)	measured
Clay blends (head)	masses 0.08 to 0.15 H, plane clips 0.02 to 0.03 H, lids 0.012 H	example [added]
Jaw	bigonial 0.90 to 1.00 x bizygomatic (example 0.93); ramus-to-base angle 124 degrees in the example	Thelen; example [added]
Eyes (stylized)	radius 0.064 H, lids 0.012 H thick, upper margin 21 degrees above center	example; 14 degrees read sleepy
Hair	clumps 0.065 to 0.115 H radius, rising 0.8 x radius, from the hairline back; base 0.008 to 0.02 H	example [added]
Corner move that reads	about 1/8 of mouth width (8 mm on 65 mm, 0.03 H); invisible at 1/30	measured
Pixels per mm	bust fills 1080 px: 2.8; bust 270 px tall: 0.75	measured (framing)
Smooth strength	0.2 (5.2 default 0.7)	Henning
Crease resolution	at least 3 to 4 vertices across the radius	Ryan King
Review lens	85 to 95 mm perspective	Morren, Kaspar, Naydenov, Yan
Landmarks	eye line 0.5 H; nose bottom halfway brow to chin; lip parting 1/3 nose to chin; ear nose base to brow; width H/1.5; mouth corners under eye centers; canthal tilt about 8 degrees; neck about 15 degrees forward	Abbitt, Naydenov, Thelen

Quality gates

• Measurable: S.stage_report(obj, voxel) (components 1, non_manifold 0, stretch p95/median under 2.5, mirror_max under 1e-4 before asymmetry). S.lower_face_report(head, H): ball True means the lower face fits one sphere within 10 % and twice as well as a plane (calibrated: the three E2 balloon jaws 0.057 to 0.082, the baseline 0.18 to 0.20, the v2 example 0.23 to 0.26). S.profile_rhythm(obj): chin out, in, lips out, in, nose out (a nose hanging below the nose base hides the lip beats). sc.planarity(c, r) for a stated plane.
• Visual (the gate): S.long_lens_render or final_render at 85 to 95 mm from front, profile, three-quarter and below, plus bx_review.review(..., modes=("silhouette", "matcap")) for the ortho silhouette. Order: silhouette, big planes (cavity off, or mode="flat"), below and above, lines, character read at thumbnail size. Rubric: references/critique.md.

Common mistakes

Mistake	What it looks like	Fix
rounded_box or ellipsoid jaw, heavy smoothing	balloon lower face: cheek, jaw, jowl one sphere	Clay jaw block with stated planes; lower_face_report gate
Flatten or scrape dabs to "make planes"	facets that follow the ball	stated planes: Clay clips, plane_cut, corner_cut
Plane cuts on a wrong mass	gem facet with a rim, metric passes	move or rebuild the mass first, then cut
Jaw block with its front ahead of the mouth	a mask or slab over the lower face	jaw behind the mound; front belongs to mound and chin
Tall jaw block, small blend	a panel edge across the cheek	low block, 0.15 H blend upward
Socket wider than the lids	ring groove, eye bags	socket 1.1 x eyeball, lid blend 0.012 H
Lids reaching behind the eye equator	sealed pocket, 3 components	clip lids at the eye center plane
Uniform hair offset, or clumps on a thick cap	helmet ledge, beanie with worms	thin base, clumps make the volume
Clumps starting behind the hairline	bare headband over the forehead	start clumps at the hairline
Symmetrizing asymmetric parts	swept hair mirrored, center seam	to_object(..., symmetric=False)
Crease projected across a grazing surface	parallel cracks	crease only surfaces facing the view; skip it
Smile sculpted into the basis	asymmetry cannot be removed	neutral basis, write_shape_key
Corner moved 1 to 2 mm	expression invisible	about 1/8 of mouth width, check pixels
No hair or costume	bald mannequin	cue list in stage 0
Detail before proportions	lines on a wrong skull	stay coarse until the gates pass
Stroke snapped with nearest from far away	groove on the nose tip	on_surface(p, view)
Mask survived the remesh	a region refuses every brush	remesh_stage clears it
GUI strokes with the view zoomed out	whole mesh flattened	bx_gui.set_view(frame=obj), check view_distance
Hairline as one tilted cut	a garrison cap from the side, vertical wall at the front	hairline as a function of azimuth (sideburn, over the ear, down to the nape), quiff ramp from the hairline over about 0.12 H [eval]
Mirrored eyes	no gaze, a staring or blank attitude	two aimed eyeballs; lid margin and brow angle are attitude dials (level brows for a neutral basis) [eval]
Feature attached at two points	a nose that floats in profile, see-through gaps	ray-grid silhouette-hole probe per view; give a big nose a side wall to the cheek; bx_audit self-intersections after the last remesh [eval]

Blender 5.2 notes

• Headless CRASH (segfault): sculpt.symmetrize, sculpt.mesh_filter, paint.mask_flood_fill, sculpt.mask_filter, sculpt.face_sets_create, sculpt.face_sets_init, object.voxel_remesh in Sculpt Mode. Poll fails: sculpt.brush_stroke, sculpt.set_pivot_position, sculpt.detail_flood_fill, trim gestures. Work: paint_mask_extract, brush.asset_activate, Edit Mode mesh.symmetrize, quadriflow_remesh, multires ops.
• OpenVDB ships with Blender 5.2 (import openvdb): FloatGrid.copyFromArray + convertToQuads mesh the Clay.
• Brushes are Essentials assets; Flatten, Fill, Scrape are one Plane type; size is a diameter; Draw Sharp defaults to SUBTRACT. sculpt_tool is sculpt_brush_type.
• Voxel remesh output is flat shaded (shade_smooth()), keeps attributes (mask included), drops shape keys.
• NumPy 2 in Blender: np.ptp(a), not a.ptp().

References

• references/procedures.md: tested code for every stage (Clay recipe, planes, form check, hair, lids, expression, final render, crash matrix, brush table, GUI recipe); load before writing any sculpt script.
• references/expert-notes.md: principles by expert with timestamps; load when designing a character or choosing methods.
• references/critique.md: stage rubric with blockers; load at every gate.
• references/sources.md: the 27 source videos with best timestamps.
• Example: tests/code/blender-sculpting/stylized_head_blockout.py (13 s, renders in stylized_head/stage_N/); comparison: tests/code/blender-sculpting/compare/compare_sheet.png.