Sizing is a very dilute, gluey substance applied to a surface to prepare it for coating or printing. It works by filling in pores and creating an even, consistent absorbent layer, ensuring that inks, paints, or photographic emulsions adhere uniformly.
In photography and printmaking, proper sizing improves image quality, prevents blotching, and enhances the longevity of the final work by stabilizing the surface before additional treatments are applied.