Definition: Craquelure is a term used for the network of fine cracks that can appear on a painting, either over the whole painting or just in parts. (Take a look at an example ofcraquelure from the Fine Arts Conservancy.)
Craquelure differs depending on whether the painting was done on canvas or a wooden panel, as well as by what was used for the ground and the type of paint used. It's said an experienced art expert can distinguish between different types of wood used as a supportaccording to the craquelure that's developed, which follows the grain of the wood.
Eric Hebborn's book The Art Forger's Handbookcontains instructions on how to create craquelure, and how to preserve cracks in an old grounds that is being reused, to create an authentic feel to a painting in the style of an Old Master.