Craquelure
This is usually differentiated from crazing, which is a glaze defect in firing, or the result of aging or damage.
Understanding the mechanism of craquelure formation in paint and the resulting crack morphology provides information about the methods and materials used by the artists.
This links the crack patterns with specific time periods, locations, and painting styles.
Italian painters usually used a thin ground surface, which led to their work developing skinny, thin cracks, while French painters have swirling cracks because of a much thicker ground surface.
During drying, the pictorial layer tends to shrink as volatile solvents evaporate.
This localization results from capillary forces, which constrain drying stresses to the free surface of the painting.
[2] Drying cracks are usually isotropic due to the fine dispersion of pigment particles within the evaporating volatile solvents.
Crack width is heavily dependent on the ability of the top paint layer to adhere to the sublayer.
Poor adhesion can occur if the painter mixes too much oil or other fatty substance into the sublayer material.
the surface energy of this layer, Z a dimensionless constant that depends on the cracking pattern, and
[2] The spacing of cracks during drying depends strongly on the stiffness of the support, or sublayer.
Changes in the relative humidity during the drying process affect both the ground layer and support of a painting, promoting crack propagation.
Paintings involving hygroscopic materials like wood supports or gesso ground layers are especially susceptible to variations in relative humidity.
[3] Variations in RH cause highly non-uniform tensile strains across the gesso surface, and when the material contracts upon drying, it fractures.
The increased strains on the convex side of the cupped wood panel causes further fracture in the ground layer as it dries.
[5] Compared to their drying counterparts, aging cracks are sharper, deeper, and are developed over the lifetime of the painting.
[2] This type of craquelure is much more difficult to predict and model because it depends on the specific environmental changes and chemical aging reactions the paint is subjected to.
Critical processes that contribute to aging craquelure include direct impacts, gradients in temperature and relative humidity, support deformation, restoration processes like canvas reinforcement and stretching, and oxidation reactions that make the surface chalky or more brittle.
In general, the pictorial layer becomes more brittle as it ages, which makes it unable to accommodate the stresses induced by environmental factors.
Art forger Eric Hebborn developed a technique and Tony Tetro discovered a way to use formaldehyde and a special baking process.
[6] Craquelure is almost impossible to accurately reproduce artificially in a particular pattern, although there are some methods such as baking or finishing of a painting by which this is attempted.
[7] Craquelure is frequently induced by using zinc white paints as the underlayer in pentimento techniques.
[8] Craquelure affecting the glaze in ceramics may develop with age but has also been used as a deliberate decorative effect, which has a long history in Korean and Chinese pottery in particular.
It is typically distinguished from crazing, which is accidental craquelure arising as a glaze defect, although in some cases, experts have difficulty in deciding whether milder effects are deliberate or not.
The crackle may take some time to appear after firing and is probably mainly caused by rapid cooling[12] and perhaps low silica in the glaze.
The modern decor industry has used the technique of craquelure to create various objects and materials such as glass, ceramics, iron.
Mixing different brands of ready-made products to mimic craquelure results in various sizes and patterns of cracks.
[13] Methods that utilize craquelure as a means of detecting art forgery have been proposed.
Historical craquelure patterns are difficult to reproduce and are therefore a useful tool in authenticating art.
Modern detection techniques rely on feature extraction at crack junctions and image matching to verify the authenticity of artwork with high accuracy.
