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
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.