n. ~ 1. A substance used to fill the pores in fibrous materials. - 2. The process of treating materials with such a substance.
Sizing is commonly added to paper, either by adding it to the pulp during manufacture or by coating the surface during finishing. Sizing gives paper a smooth surface that prevents ink from bleeding into the fibers. In some photographic processes, the paper is sized to keep light-sensitive salts on the surface in order to increase image sharpness. Sizing is commonly made from starch, gelatin, alum, albumen, or rosin.