Moire

Moire, or Spanish Wave is an effect that manipulates the brightness of a marbled pattern. The overall effect is of light and shadow, as if the paper is ruffled or folded up.

With traditional marbling, the Moire effect is achieved by moving the paper while removing it from the bath. With Digital Marbling, it is a mathematical function applied to each pixel. This means that there are real (physical) Moire patterns that are difficult to replicate digitally and that you can generate digital Moire patterns that would be impossible in real life.

This is a Chevron pattern overlaid with a Moire pattern consisting of straight, parallel lines.

This is a Moire pattern which is easy to produce digitally, but (I assume) would be impossible to create physically.