As we age, we have a lot in common with paintings and some of the condition issues that plague works of art. Our skin is like the surface of an oil painting, affected by time, environmental variables and our genetic makeup. The fine lines and wrinkles that emerge on our faces as we enter mid-life are analogous to the lines and cracks that develop on the surface of a painting, known as craquelure.
Craquelure is the term used to describe a network of fine cracks in the paint and/or varnish of a painting. The word derives from the French verb craqueler which means literally “to crackle”. Because craquelure forms as paint ages, it is the most common condition issue we see with older paintings and can often help to date a painting or determine a forgery.
As paint dries on the canvas it shrinks and becomes less flexible and the canvas itself loses some of its tautness over time. This combination causes cracks in the paint to form where the physical stress to the surface is greatest. Generally the cracking is greatest at the outer edges of the canvas where there is more stress from the canvas slacking closest to the stretcher. Cracks caused by a slackening canvas are different than those caused by ageing paint, though they often exist on the same painting. Fine cracks also happen during the drying process, when two layers of paint dry at different rates, creating a brittleness between the layers.
The pattern of the craquelure in the paint surface depends on where, when and how the painting was made, and under what sort of conditions it has been stored. There are different styles of craquelure in French, Italian, Dutch, and Flemish painting, relating to differences in materials and techniques used. Typical French craquelure, for example, has curving cracks in larger and less regular patterns, while Italian craquelure is usually smaller with rectangular “blocks” of cracking. The English style of craquelure often displays blisters to the surface caused from the use of bitumen, a type of asphalt, in the paint, a technique first used by Sir Joshua Reynolds. Changes in humidity and temperature affect the way craquelure develops, as do the type of pigments used. Both of these variables have regional consistencies that allow researchers to connect different “styles” of craquelure with different countries.
Authentic craquelure is difficult to replicate or forge because it is almost impossible to artificially reproduce a specific pattern of crackle. For this reason, art historians and conservators are often able to use the appearance of craquelure to help authenticate an old painting. Forgers of Old Master paintings have used a technique called induced craquelure that uses formaldehyde and a special baking process to create cracks in a newly painted surface. This technique creates craquelure, but the cracks tend to be very uniform in appearance and do not resemble the irregular patterns of authentic craquelure.
While we usually associate craquelure with old paintings, it is not uncommon to see cracking in the surface of 20th century paintings that have been exposed to extreme changes in temperature and/or humidity, or those that were painted on unprepared supports or with low-quality materials. Acrylic paint, in particular, has a propensity to crack when it has been thickly applied and has been exposed to very low temperatures. Certain paint colors, because of how they are made, are more problematic than others. Paint colors are made up of ground pigment, the coloring agent that is mixed with a liquid agent and often a drying agent. Some pigments dry poorly without the addition of a special agent and are more susceptible to cracking over time. Many French painters had an allegiance to a specific art supplier, and paintings by painters who purchased from the same purveyor often exhibit the same type of craquelure pattern which is due to the similar preparation of the canvas and the mixture of paint they used.
Craquelure is also seen in the glaze of ceramics both old and new. As with paint, crackle develops in glaze with age and can be seen on many types of glazed pottery. Deliberate craquelure has also been used as a decorative effect and has a long history in Korean and Chinese porcelain. The modern décor industry uses the technique of forced craquelure to create objects that look old in materials such as pottery and metal, often seen in garden statuary and urns.