Cracking
The formation of cracks on paintings is called cracking . A distinction is made between "shrinkage cracks" and "age cracks".
The former is either a technical failure by the artist or a conscious stylistic device . Often the reason for this is the difference in tension between the layers of paint. B. if a (oil) painting layer is not yet completely dry and is being painted over. Then the lower layer of paint will “blast” the upper layer of paint as it dries due to its increase in volume (oils do not dry, but oxidize. See: Linseed oil ). The impressionists consciously accepted the formation of cracks in order to be able to use the application of paint in several still wet layers as a design element.
The "age cracks" stem from the lack of flexibility of the paint layer, as is characteristic of old pictures. The picture carrier breaks the paint layer with its movements. Wood “works” a lifetime, and canvas is flexible.
Artificial cracking
In Antiques - counterfeiters and art forgers , there are some procedures that the premature aging will cause the images with the corresponding cracks. But mostly the cracks differ under the microscope . Often the artificial cracks do not go through the primer because only the upper layers of paint were exposed to the process. In general, therefore, the back of the pictures usually reveals more about their history than the front.