Chapter 2 – Dirt maps and drip logic

Chapter 2: Dirt Maps & Drip Logic

Created by Sarah Choi (prompt writer using ChatGPT)

Dirt Maps & Drip Logic

Wear, Weathering & Damage for Costume Concept Artists (Scuffs, Stains, Tears, Repairs)

Equally useful for concept‑side ideation and production‑side handoff. Plain, visual language for concept artists.

1) Why dirt maps?

Dirt maps are the directional storytelling layer of wear. While stress maps tell you where friction concentrates, dirt maps tell you how substances travel over a body in motion—guided by gravity, wind, fabric structure, seams, and habit. Mastering drip logic converts random grunge into readable cause‑and‑effect: viewers can guess the weather, the work, and the last 10 minutes of action from the stains alone.

Design rule: pick 1–2 substances + 1 motion state + 1 material. Then let physics do the rest.

2) Mini‑physics for believable stains

Gravity: pulls liquids downward, bending around convexities (knees, shoulders) and pooling at horizontal breaks (cuffs, pocket flaps).
Viscosity: watery → long, thin rivulets with speed lines; oily/syrupy → short, fat teardrops with rounded noses.
Surface tension: creates beads on hydrophobic coatings (DWR), sharp tide rings when water evaporates.
Capillary action: wicks moisture upwards in hems, cuffs, and seam allowances → thin, feathered halos above an initial wet zone.
Porosity/nap: open weaves and raised naps trap particulate → matte, dusty patches; tight coatings shed into rivulets and sheet flow.
Impact/splash: angle + velocity control spatter crowns, forward bias, and droplet size gradients.

Keep these five in mind: down, pool, ring, wick, speckle.

3) Substance taxonomy (quick picker)

Substance	Fresh look	Dry look	Color drift	Notes
Rainwater + dust	soft rivulets, sheet flow	faint tide rings	towards neutral gray/brown	accumulates at hems/cuffs; reads clean‑dirty contrast
Mud (clay‑rich)	thick splats, ropey drips	cracked plates	shifts lighter as it dries	spatter cone from behind legs when walking
Mud (silty)	smooth skins	powdery dust	desaturates	forms long splash tails
Oil/grease	dark, semi‑gloss halos	permanent dark patch	warms (amber)	halos around center; resists laundering
Blood (fresh)	high surface tension beads	brown‑red matte	darkens, then cools	directional tails if running; capillary bloom in knits
Salt/alkali	translucent wet	pale crystalline ring	lightens	tide lines at hems/cuffs in winter, under armpits
Rust	faint orange smears	granular freckles	orange‑brown	below metal hardware, rivets
Sap/resin	strings, sticky webs	amber glossy nodes	amber	collects fibers/debris; hard to remove
Soot/char	soft smudge	dry matte	cools toward black	concentrates at elbows, cuffs, collars; smoke plume logic

Pick two for clarity in a single look.

4) Directionality models (how drips actually flow)

Standing still (rain): vertical rivulets; shoulders shed to sleeve caps; water collects at elbows (if arms bent) and hem.

Walking: front thighs get forward‑tilted speckle from oncoming spray; backs of calves/heels catch upward fans from foot strikes; hems show rear‑biased mud flick.

Running: longer comet tails; higher speckle density behind shins; diagonal bias across coat skirts; elbow drips stretch toward cuffs.

Crouching/kneeling: knee plates show outward starburst of mud; thigh tops mostly protected; cuff interiors get ground transfer.

Riding (horse/bike): right/left asymmetry from mount side; chain oil on inner right hem; fan‑shaped rear splatter up the back vent.

Climbing: chest and forearm leading edges dirty first; gravity breaks on belt seam → ring above waist.

Seated work (desk/bench): forearm drags → cuff grime bands; thigh tops polish without drips; elbow specks aim backward.

Shortcut: Sketch 3–5 flow arrows on the figure before painting stains. Make sure arrows converge at hems, cuffs, vent tips, pocket flaps, and seam intersections.

5) Garment zone atlas for dirt

Shoulders & yokes: rain sheet flow, seam‑guided channels; clean islands under hoods/epaulets.
Sleeves: drip transfer from hands; elbow dam forms a ring if arms bent in rain.
Cuffs (sleeve & hem): capillary wicking bands, salt rings, edge mud.
Front thighs: forward speckle while moving; diagonal tails from run stride.
Back calves & heel counters: fan‑spray from foot strikes; pebble pocks.
Skirt/duster hems: rear‑biased mud wedges; side gores sculpt splash edges.
Collars & plackets: vertical gutters; sweat‑salt mix; makeup/foundation transfer.
Pockets & flaps: drip breaks → small crescent tide marks under the lip.

6) Drip & splatter typology (visual shorthand)

Beads: discrete dots with tiny highlights; seen on waxed/oiled cloth, fresh rain on DWR.
Rivulets: thin, slightly meandering lines that merge into thicker tracks; taper toward tail.
Teardrops: heavy head, short tail; characteristic of viscous fluids (oil, resin, clay‑rich mud).
Sheet flow: wide value shift with soft edges; interrupted by seams/pleats creating micro‑steps.
Crown splatter: impact ring with outward spikes; inner void remains light; strongest on thigh/shin fronts.
Back‑spray fans: triangular fields of speckle pointing up the back of legs/coat tails.
Tide lines: hard, thin rings at the drying edge; often nested; classic at cuffs/hems.
Wick halos: ghostly, feathered bands just above hems and seam allowances.

Use three scales per stain event: a) macro field, b) medium tracks, c) micro speckle. The hierarchy sells realism.

7) Material grammar (how fabrics translate dirt)

Denim/twill

Holds strong tide lines; whisker catch in crotch/thigh; mud dries to chalky plates; oil blooms warm.

Wool/melton

Nap traps soot into matte patches; water makes soft, fuzzy rings; little rivulet definition; pills collect grime.

Leather/coated canvas

Rivulets are sharp and glossy; pull‑up lightens around bends; dried salt crystals pop; oil darkens permanently.

Knits/jersey

Capillary bloom is dominant; rings feather outward; beads are rare; ink/blood travel along loops → irregular edges.

Synthetics (nylon/poly/softshell)

Strong bead and rivulet behavior; dirt bands show as value only until coating wears; seam tape edges collect crisp grime.

8) Color, value & roughness cues

Water‑only: slight darkening when wet → returns near base value; use subtle roughness increase (matte) after rain dries on natural fibers.
Dust/mud: lower value + slight warm shift; edges can lighten as crust lifts.
Oil/grease: strong value drop; lower roughness (shinier); soft halos.
Salt: higher value ring, low saturation; micro‑sparkle in spec.
Soot: low value, low saturation, very matte; blunt edges from smudge.

Stack value first, hue second, roughness third for quick reads.

9) Concept‑side workflow (A/B/C passes)

A — Flow pass:

Sketch flow arrows and 3–4 accumulation zones (cuffs, hem back wedge, calf fans, pocket lips).
Block macro fields: wet panels, mud areas, soot clouds.

B — Track pass:

Lay rivulets and tails with varied thickness; break tracks at seams; add tide rings.
Reserve 1–2 hero drips that cross a silhouette edge for readability.

C — Micro pass:

Speckle gradient: largest near source, smaller outward; add 3–5 random interrupters (stitches, rivets) where dirt dammed.
Drop one repair inside a dirty field to tell time (patch older than stain? show overlap correctly).

LOD guidance: at gameplay distance prioritize hem bands, calf fans, and cuff rings; save micro speckle for closeups.

10) Production‑side: masks, shaders, decals

Suggested packed mask:
- R: Dust/mud intensity (broad fields)
- G: Liquid tracks & tide rings (rivulet/drip)
- B: Oil/grease (gloss control)
- A: Salt/alkali highlight (adds sparkle/roughness contrast)
AO as dirt catcher: multiply dirt by bent‑normal/AO around seams, pockets, elbow darts, knee pleats.
Vertex colors: paint flow guides (e.g., blue channel drives gradient from shoulder → cuff). Useful for tunables at runtime.
Unique vs tiling: tilers hold micro grit; unique masks paint macro flow shapes (back‑spray wedge, hem bands, shoulder sheet flow).
Decals: for events (fresh drips, splatter crowns, signage paint). Place tangent‑aligned for fabric; world‑aligned for thrown mud.
Roughness logic: reduce roughness on oil channels; raise on dried mud; vary within a single drip for life.

11) Seam & pattern logic (the dirt dam)

Seams are dams and gutters. Top‑stitched ridges catch speckle on the windward side; piping creates bright clean edges below.
Pattern pieces set flow resets—every join is an opportunity for a tide line. Mark them on your mask sketch.
Pleats & gores split sheet flow into ribs; flaps cast dry shadows (clean triangles beneath).

12) Case studies (concept → production)

Storm courier (duster + bike)
- Concept: rain → sheet flow from yoke to skirt; back‑spray fan from rear wheel; chain‑oil freckles inside right hem.
- Production: unique mask for yoke sheet flow; decal fan on skirt back; separate roughness channel for oil.
Field naturalist (wool coat + canvas trousers)
- Concept: dew‑soaked grass → hem wick halos; knee mud plates; pocket‑lip crescents; resin nodes on sleeve.
- Production: AO‑weighted dirt at pocket mouths; parallax micro‑crackle for dried mud normals; resin drips as glossy decals.
Dock worker (synthetic shell + rubber boots)
- Concept: brine splash → salt tide rings at cuffs; rust tears from rivets; soot smudge at collar.
- Production: alpha‑masked salt rings in A‑channel; rust streak decal below hardware; collar roughness lift for soot.

13) Common mistakes (and fixes)

Even gray grunge: pick a flow direction and 2–3 accumulation sites. Erase elsewhere.
Drips that ignore gravity: add down‑vector; curve over forms; stop on seams.
Muddy faces: protect silhouette reads—keep face, chest logos, and hero shapes partially clean.
Spatter scale mismatch: ensure droplet size shrinks with distance from impact; avoid uniform dot fields.
Oil identical to water: darken, reduce roughness, add soft halo; no tide ring.
Salt drawn too dark: remember salt raises value; keep edges thin.

14) Variant matrix template

Variant	Shoulders/Yoke	Sleeves/Cuffs	Thighs/Knees	Calves/Heels	Hem/Skirt	Notes
Clean	none	none	none	none	none	material reads first
Wet	sheet flow, no rings	elbow dam ring	vertical rivulets	faint back fan	dark band, zero tide	wet gloss
Dry	faint tide rings	cuff halo	weak tails	light speckle	first ring	restore base gloss
Crusted	dust film	wick band + salt	mud plates	pebble pocks	layered rings	roughness up
Oily	n/a	small halos	tool‑print stains	n/a	dark wedges	roughness down

15) Quick exercises (skill‑builder)

5‑arrow plan: On a blank figure, draw five arrows for flow and place three accumulation zones. Paint only those.
One‑substance studies: Do 3 mini‑studies: (a) rain on synthetic, (b) mud on denim, (c) oil on leather.
Event flipbook: Paint Clean → Wet → Dry → Crusted for one garment using the Variant matrix.
Seam dams: Take a vest with many panels; paint sheet flow that stops at each seam—mark rings.

16) Prompt seeds for reference boards

“Back‑spray mud fan behind runner’s calves, high shutter speed.”
“Salt tide rings on winter coat cuffs macro.”
“Rivet rust tears on waxed canvas bag.”
“Rain sheet flow over shoulder yoke with seam gutters.”
“Clay mud impact crown on denim thigh, drying stages.”

17) One‑pager template (copy/paste)

Garment: ______ Role: ______ Environment: ______

Substances: Rain □ Mud □ Oil □ Blood □ Salt □ Soot □ Rust □ Other: ____

Motion state: Stand □ Walk □ Run □ Ride □ Kneel □ Climb □ Sit □

Flow arrows sketch attached: Yes □ No □

Accumulation zones: Shoulders □ Cuffs □ Thighs □ Knees □ Calves □ Hem □ Pockets □ Back vent □

Material behavior notes: __________________________

Mask/shader plan: R dust | G liquid | B oil | A salt

Roughness notes: _________________________________

Decals/events: ___________________________________

Asymmetry: ______________________________________

LOD: Gameplay vs close‑up ________________________

Final reminder

Start with arrows and accumulators, limit your substances, and let material physics dictate the mark‑making. If someone can point to a cuff ring, a back‑spray wedge, and a tide line and tell you what just happened, your dirt map is doing its job.