One of the most annoying features of watercolour painting and some printing techniques. Cockling drives me mad at times as it is usually the artist's original mistake of not having stretched the paper properly before painting. This means that when the paint dries, the paper contracts forming ridges. It can be flattened but it's not easy and not always possible. Trying to mount a cockled watercolour gives most framers a real headache. However, the most important item is the painting and a little cockling should not spoil ones enjoyment of a fine painting.