The ink is rich, opaque acrylic pigment, not thin watercolor. Light shades sit on top of dark paper and dark surfaces without turning chalky, and the color stays vivid as it cures. Paper, sketchbooks, canvas, wood, rocks, glass, ceramic and general craft work — the acrylic film rests on the surface instead of soaking in, which is why coverage stays solid across materials. On glass, glazed ceramic and other smooth surfaces, seal the finished piece for extra durability.