Creases may be caused by accidental damage or improper storage. Treatment may include “drumming” on to Japanese paper to flatten the paper.

Undulations, effectively bumps and bulges in the painting, may be caused by raised humidity and due to the hygroscopic properties of paper (water absorbent), controlling the humidity can help prevent the initial structural distortions.

However, if already faced with a watercolour presenting an undulating surface, humidifying treatment in combination with the application of pressure and tensioning the paper, carried out by a trained conservator can even out the structure of the watercolour creating an even surface.