WASHES · REFERENCE GALLERY · THE FOUNDATION

Computer-Generated Watercolor

Curtis, Anderson, Seims, Fleischer & Salesin. SIGGRAPH '97, pp. 421–430. The three-layer water / pigment / paper model Washes is built on.

Paint on the canvas below. Each stroke deposits water and suspended pigment; the wash then dries from the rim inward. As water evaporates at the boundary, interior water flows outward to replace it, carrying suspended pigment with it — pigment accumulates and deposits at the receding edge. That migration is the source of watercolor's signature dark rim, and it is the paper's contribution to the image, not the painter's.

This is a deliberately simplified version of the Curtis pipeline (no full shallow-water solve), but it keeps the three layers — water, suspended pigment, deposited pigment on textured paper — and the two effects that define the look: edge darkening and granulation. Both have kill switches so you can see exactly what each one contributes.

Edge darkening (pigment migrates to the drying rim) Granulation (pigment settles into paper valleys)

Drying speed

Click or drag to lay down a wet wash, then let it dry.

Try this

1. Paint one blob and let it dry untouched. Switch to the suspended-pigment view mid-dry to watch the pigment crowd toward the shrinking boundary before it deposits.

2. Clear, turn off edge darkening, and paint the same blob. It dries to a flat, even stain — gouache, not watercolor. The rim was doing all the work.

3. Toggle granulation with the paper-height view open. The pigment's grain pattern is the paper's noise field made visible — deposition is biased into the valleys, exactly the coupling Curtis et al. use to get pigment texture for free from the paper model.

4. Drop a fresh wet blob overlapping a half-dried one. The new water re-wets the boundary and pushes the old rim outward — a primitive backrun.