Linseed Oil

As Mike said, we recently moved on to discussing chemistry and how it relates to art, specifically in the context of authentication, restoration, and analysis. One specific case we discussed in class was the restoration of a lunette depicting the adoration of the Virgin Mary and the infant Jesus by two angels in the church of Santa Maria la Vetere. The original beauty of the lunette was covered by a thick yellow-brown patina, the result of a layer of plaster being applied over the entire area of the lunette. However, restoration began on this lunette before a proper chemical analysis of the various layers could be performed. As a result, a large area of the hair of one of the angels is irreversibly colored red.
Had a proper analysis been performed before restoration began, the restorers would have known that there were two layers of gilding on the lunette. The first layer was applied using the Armenian bole technique while the second was applied using linseed oil. If the restorers had known about the presence of these two layers, they would have been able to alter the restoration techniques they used in order to take the presence of the materials specific to each application process.
Linseed oil is made from the seeds of the flax plant. Because of its polymer like properties, it can be used as a pigment binder in oil paints and as an adhesive for gilding. The oil is composed of a mixture of various triglycerides that differ in their fatty acid constituents. The oil has a high content of unsaturated esters, however, which allows the oil to polymerize and harden upon exposure to oxygen. Consequently, if a thin layer of gold sheet is placed on a surface that has been treated with linseed oil, the oil will eventually harden upon reacting with oxygen in the air, binding the gold sheet to the surface.