A composition roller is a tool used in letterpress printing to apply ink to a bed of type in a printing press. It consists of a cylinder made of a substance known as "roller composition" or simply "composition", a mixture of hide glue and sugar (in the form of molasses or treacle), with various additives such as glycerin depending on the particular recipe. Early recipes also included gypsum plaster and tar, though these were eventually found unnecessary.
Before its invention, most inking of printing presses was done by manually pounding the type with ink balls, specially treated leather balls stuffed with wool. The difficulty and time involved in making and using ink balls led to various attempts to use cylinders, which could be rolled rather than pounded. Leather rollers (or "skin rollers") were attempted, and were used on the earliest steam-powered cylinder presses, yet these did not work as well as the ink balls, and the stitching seam would appear on the printed type.
