Whole egg, yolk or white may be used as a tempera medium. The egg yolk is a stable emulsion of an aqueous liquid with an oily, proteinaceous medium which dries quickly into a hard, insoluble film. It is the traditional tempera medium and may be mixed with oil and/or resin for painting. The white of the egg is used as a size for attaching gold leaf. Albumen is the adhesive substance of egg white. As a pure film, albumen is clear, brittle and water soluble. Water solubility can be decreased by heating or adding tannin. Museum of Fine Arts, Boston (2000). [J. Cassar, R. de Angelis]