Wet-on-Wet Watercolor Diffusion & Granulation Studio

This simulation is about what happens to watercolor pigment after the brush leaves the paper. A wetness field tracks how damp each part of the sheet is; pigment can only migrate through that film of water, spreading by a diffusion process that switches off cell-by-cell as the paper dries. Pick a pigment — staining dyes like Phthalo Blue and Quinacridone Rose, or coarse granulating earths like Payne's Grey and Burnt Umber — dilute it with more or less water, and paint onto a textured cold-press sheet. Granulating pigments visibly settle into the paper's micro-texture as they dry, and dragging fresh wet colour into an already-wetted area (or pressing "Wet whole sheet" first) triggers real capillary backruns and cauliflower blooms at the drying edge, exactly the effects wet-media painters chase and fight.