Sarah Clarity Studios

Chapter 2: Wear Patterns: Edges, Contact, Stains, Moss, Rust

Created by Sarah Choi (prompt writer using ChatGPT)

Wear Patterns — Edges, Contact, Stains, Moss, Rust (Material Systems, Aging, and Weathering for Environment Concept Artists)

Why wear is the memory of use

Wear patterns are not decoration; they are records of contact, gravity, water, time, and intent. A scene gains credibility when edge softening reveals years of touch, when stains trace the path of water and oil, and when moss and rust emerge only where physics permits. This article explains the mechanics behind common wear signatures—edges, contact polish, stains and streaks, biological films, and corrosion—and shows how to turn that logic into concept language and production‑ready systems.

The grammar of edges

Edges age faster than fields because they concentrate stress and contact. Sharp arrises chip where impacts occur and round where hands slide. In masonry, corners spall as microcracks radiate from hits and as freeze–thaw wedges flakes away; protected interior arrises stay crisp while windward faces round first. In wood, arrises lose paint earliest, exposing brighter fibers that gray over time; stair nosings polish at the toe line and dent at consistent intervals where feet land. In metal, edges shed coatings from abrasion, revealing primer or bright base that immediately oxidizes; guard rails brighten on the top tube from hands and dull beneath where grime clings. In concrete, exposed edges uncover aggregate and show micro‑shadowing; chipped corners leave angular scars with darker dirt halos.

When painting or modeling, decide which edges are touched, which are hit, and which are only weathered. Hand height on railings, hip height on jambs, bumper height on dock corners, and broom height on baseboards are dependable bands. Rounding should be directional and uneven, heavier on the approach side of door jambs and on the windward side of parapets. Fresh chips read lighter and sharper; old chips darken and soften; repairs interrupt with new, crisp geometry.

Contact polish and traffic fields

Surfaces in motion paths polish while adjacent areas stay matte. Stone steps reveal bright troughs down the center of the run, with darker shoulders that collect dust; the landing at the top spreads wear where turning occurs, forming a fan of polish. Timber floors develop satin lanes leading to doors and sinks, while corners under furniture remain dull and dusty. Metal thresholds glow where wheels and boots cross; checker plate smooths along a diagonal where carts twist. Hand‑contact zones on doors, push plates, turnstiles, and elevator buttons shine with a warm specular and carry subtle finger oil halos; paint erodes exactly where repeated touch occurs. Roadway wear shows in tire tracks that darken and smooth asphalt, with finer grit swept to edges; in yards, forklift paths draw looping figure‑eights with rubber scuffs and chipped curb edges.

To encode traffic fields, trace believable desire lines and let roughness drop one notch along them, then feather back into base. Keep polish narrower on stairs and wider at doors, and add micro‑scratches aligned to the direction of motion. Where traffic changes seasonally, establish layered states: salt and grit crusts in winter, dusty matte in dry seasons, and darkened wet bands after rain.

Stains, streaks, and runoff paths

Staining is gravity made visible. Water carries dissolved minerals, fines, oil, and organic matter; where it slows or evaporates, it deposits. Beneath parapets, coping stones, and flashing edges, vertical streaks form in lines that match drip points and joints. Lime leaches from concrete as white veils under persistent leaks; rust tears fall from every fastener that gets wet; oils descend from machinery and gather in low points as dark, glossy pools with iridescent sheens. On facades, sheltered zones blacken from soot while exposed zones self‑clean in the rain, creating two‑tone patterns beneath overhangs. Under handrails, thin curtains of water form on rainy days and leave fine stripes; at sill edges, hard water dries into crescent arcs on glass and mineral blossoms on stone.

For credibility, pair every stain with a source and a flow path. A rust streak needs a corroding component above and a surface that catches the drip. A lime run needs a concrete or mortar leak path and a place where evaporation exceeds flushing. Oil requires a machine, pipe, or vehicle habit nearby, plus wind or vibration patterns that explain its spread. Avoid uniform drizzles; concentrate streaks under joints, weeps, and fasteners; leave clean wakes where drip edges throw water clear. Remember that stains lighten near edges where gravity thins films and darken in cavities where water lingers.

Moss, algae, and biological films

Life favors shade, moisture, and stillness. Algae establish first as thin green films on consistently damp, smooth surfaces such as north‑facing stone, painted concrete, or glass near sprinklers. Moss follows in rough, cool, shaded concavities where water lingers, especially on mortar joints, stone caps, and soil‑contaminated cracks. Lichens colonize relatively stable, low‑nutrient stone faces and grow in slow, pale disks that ignore small water events. In warm, humid climates, black mildew streaks appear under eaves and on soffits where condensation nightly wets surfaces. In arid places, biology retreats to irrigation overspray zones, fountain lips, and seep lines; beyond that, rock varnish and salt crusts dominate instead of moss.

Place growth where a wetness mask would predict it: leeward of prevailing sun and wind, low on walls near splash zones, beneath spouts that blow back in storms, and along ground lines where soil throws spores and moisture up on walls. Keep transitions patchy and species‑specific: a moss pad reads as a low, velvety cushion with high micro‑roughness; algae as a thin slick with low roughness and higher saturation; lichens as speckled, desaturated pancakes that disregard small micro‑topography. Let biology recede at drip edges and increase under obstructions where drying is slow. Add detritus where moss traps leaves and silt; leave bare scours where runoff strips growth during heavy rain.

Rust, oxidation, and metal fatigue

Corrosion is chemistry plus water and air. Bare or chipped steels bloom first at scratches, lap joints, and fastener penetrations. Under paint, filiform corrosion creeps like worms from a nick; at overlapped sheets, crevice corrosion darkens a thin line before erupting into flakes. Galvanized steel dulls uniformly to gray unless damaged; if cut or drilled, the exposed ring rusts quickly and paints a perfect halo. Stainless resists but tea‑stains in marine air, especially at welds and fasteners of lesser grade. Copper, bronze, and brass oxidize from warm brown to black to green; the runoff stains stone and concrete below in vertical tongues that widen with distance as droplets disperse. Aluminum pits in salt and forms white oxide bloom at fastener lines; zinc chalks to a matte white that streaks under gravity.

Make rust read in depth and time. Early corrosion has color without volume; late corrosion adds scale and flakes that cast micro‑shadows. In rain states, fresh streaks should appear beneath active sources and fade as surfaces dry; in dry states, the stains persist but lose specular darkening. Tie corrosion to detailing errors: missing caps on posts, unsealed cuts on guard rails, incompatible fasteners at balustrades, flat ledges where water can sit, and joints oriented against gravity. Show maintenance as part of the story with primer patches, overpaint halos, new bolts among old, and replaced panels with mismatched sheen.

Dust, soot, and air movement

Fine particles settle where air slows and escape where it accelerates. Ledges, louver tops, pipe crowns, and beam flanges collect dust in dry regimes; windswept edges stay clean. Exhaust plumes from vents draw soot ellipses on nearby walls; fan intakes keep clean halos where airflow prevents deposition. Under bridges and overpasses, tire dust paints black bands along travel lines; at tunnel mouths, portals show gradient soot that lightens with distance. In kitchens and foundries, grease binds particles into sticky films that resist rain but smear under touch, leaving lighter streaks. Map deposition to airflow: behind obstructions, inside recirculation zones, and in rain‑shadow niches.

Salt, frost, and chemical crusts

In coastal and cold regions, chemistry writes fast. Sea spray leaves salt crystals that draw moisture and accelerate corrosion; white efflorescence climbs a short way above splash height and then stops. Deicers grind into concrete and stone at entrances and stairs, leaving white bloom, pitted surfaces, and rusting hardware; the first risers and landings show the most damage. In deserts, evaporative salts grow “popcorn” crusts in seep zones and capillary fringes on walls near irrigated beds. Treat crusts as bright, matte deposits that soften color and absorb shadows; they gather in cavities and diminish on edges where knock‑off and rain occur.

Scales of wear: micro to macro

Wear operates from the millimeter to the street. Micro wear includes hairline scratches, grain lifts, and thin films that change roughness and specular only. Meso wear includes chips, spalls, drips, and pads of growth that cast small shadows and vary albedo more strongly. Macro wear includes structural sag, slab settlement, curb rounding from decades of wheels, and washouts that reshape ground. While concepting, decide which scale dominates the shot and let the others support quietly. In production, keep micro wear largely in roughness and normal, meso wear in decals and secondary masks, and macro wear in geometry and terrain.

Climate and aspect scripts

Exposure and orientation decide where wear flourishes. Equator‑facing walls bleach and crack; pole‑facing walls stay damp and biological. Windward faces polish from sand or snow scour; leeward faces collect dust and growth. Under canopies, surfaces remain dry and crisp with sharp arrises; beyond the drip line, splash bands darken bases and algae flourish. Urban canyons differ by street orientation: one side may sunbathe while the other grows mildew. Use an aspect mask derived from world north to bias all weathering and an exposure mask to reduce wear beneath overhangs.

Storytelling with maintenance and mismatch

Repair is evidence of care and scarcity. New mortar patches read smoother and brighter until they weather; replacement stones have sharper arrises and different quarry hue; welded gussets bring fresh mill scale and circular heat tint; repainted panels show brush strokes and masked edges. Mismatch is inevitable: one pane of glass is a slightly different tint, one board is newer, one run of shingles is cleaner after wind removed lichen. Place these deliberately to show chronology and to break uniform tiling. In distressed settings, show opportunistic fixes: tar daubs under a leaky cornice, rope lashings on a broken handrail, fused plastic patches on tarps. In well‑maintained districts, show annual cycles: fresh limewash lip on base courses, re‑oiled decking with tape ghost lines, replaced anodes on marine piles.

From thumbnail to shipped asset

In thumbnails, draw wear as arrows and bands rather than speckles. Mark hand zones, foot paths, drip lines, splash bands, sun sides, and wind sides. Decide which story dominates—neglect, heavy use, marine exposure, cold climate—and choose three wear mechanisms to foreground. In modeling, bevel or chip the specific edges that logic predicts, not all edges equally. In texturing, push roughness to do most of the work, with albedo shifts following only where chemistry or sediment demands. Drive decals from world‑space masks for slope, curvature, flow, aspect, AO, and wetness so placement respects gravity and exposure, and keep density higher near transitions such as the first two risers, the last meter of a parapet, and under fasteners.

In engine, author wet, dry, dusty, and post‑storm states. In wet, darken porous materials from the ground up with a vertical gradient and add active drips under sources; reduce the strength of powdery efflorescence and dry dust. In dusty, mute specular sparkle and grow edge lint on ledges; in post‑storm, leave silt fans at door thresholds and puddle rings with debris lines. Animate small effects where appropriate: slow algae bloom near persistent leaks across in‑game days, salt crust that strengthens toward the sea, and rust streaks that lengthen subtly under repeated storms.

Troubleshooting and common mistakes

Uniform edge wear reads like a filter; vary intensity by use and elevation and respect approach direction. Random grime wallpaper ignores gravity; recompose stains into vertical narratives with sources and sinks. Moss plastered on sun‑baked, windy planes breaks plausibility; return growth to shaded, moist concavities and overspray zones. Rust without runoff or a corroding source floats in space; add a fastener, seam, or cut edge above and a tear below. Perfectly even polish suggests a robot; add slight lateral bias and pauses at door pulls and turning zones. Overuse of decals at equal size creates scale confusion; mix sizes and let some wear be in material response rather than stickers.

Field exercises to train the eye

Walk a single block and record one example each of edge rounding, contact polish, runoff stain, biological growth, and corrosion. Photograph the source for each effect and trace the path to the mark. Sketch a simple plan and section marking sun path, wind, and prevailing rain. Back at your desk, paint one doorway, one stair, and one parapet in four states—fresh, service, tired, failed—by changing only masks and roughness plus a few targeted albedo and normal edits. Repeat the doorway in maritime, arid, and cold scripts without changing geometry.

Final checklist

Does every stain, patch of growth, or rust tear have a clear source and a gravity path? Are polish lanes and edge rounding placed where hands and feet truly pass? Do climate and aspect biases shift wear predictably across the scene? Are decals used sparingly to support, with roughness and normals carrying most of the narrative? Do repairs and mismatches tell a plausible maintenance story? When the answers are yes, your wear will stop being noise and start being evidence—time, touch, water, and chemistry made visible.