Small cracks may catch and hold dirt, but the removal of the dirt by a superficial cleaning in many cases eliminates the disfiguring effect. If the paint film is thick and contains too much oil, the surface may wrinkle. An improperly prepared ground layer can also cause disciguring cracks on the surface. As the painting continues to age, both the paint film and priming lose flexibility and become brittle. Expansion and contraction of the fabric support, due to absorption and release of moisture from the air, adds further strain which leads to crack formation.
Some pigments are naturally sensitive to ultraviolet light, acids or bases.
Exposure of these sensitive pigments to any of these conditions will cause them to fade. Also, treatment of a painting with either acidic or basic cleaning solutions can cause some sensitive pigments to discolor. Physical Damage Happens Cracks can also be caused by mechanical means, such as pressure, large or small, on either the front or back of the painting. Almost any marks placed on the revers of a canvas will, in the course of time, affect the surface. Writing on the back can cause the paint to flake off ont the front of the canvas, wetting of the canvas from the application of labels can cause cracks, and any sharp blow will inevitably leave its mark even if it does not rupture the canvas.