The next step after stretching the linen over the bars is to prepare the glue sizing. Rabbit skin glue comes in a crystal form and looks somewhat like cream of wheat. This is truly one of the historic materials and techniques and has been used for centuries. The crystals are soaked overnight in water and then heated in a double boiler where the crystals dissolve and the mixture is becomes clear. It is applied directly onto the linen with a large brush while very warm, working quickly to cover all the fabric surfaces, sides, corners, and backs. After it is totally saturated the canvas is placed on a flat surface to dry. The slack in the linen will become taut as it dries. Only one coating is needed. The purpose of this process is to coat all surfaces so that all the fibers are sealed and prevents the primers and paints from coming into contact with the linen. Thus it becomes archival.