Asphaltum (pigment)

A transparent brown, asphalt-based pigment used in watercolor, oil paints, and glazes, especially in the 17th and 18th centuries. It is an oily material that can slow the drying of linseed oil producing a soft film. With time, asphaltum in dried oil films can result in the movement or disfigurement of the film as well as allligator cracks. Asphaltum was sold commercially as a transparent brown artist pigment under the name "bitumen."