is a fluid or viscous compound consisting of a pigment finely dispersed in a vehicle, or varnish, that consists of resin, solvent, and additives. The pigment, which provides color and opacity, combines with the resin to form the hard film on the paper after the solvent carrier has disappeared. The petroleum solvent may range from a light, volatile material to a heavy, high-boiling oil, depending on the desired thickness and evaporative quality of the ink. Additives are used to speed or retard drying, resist oxidation, improve scuff resistance, reduce viscosity, aid penetration, and help prevent sheet sticking. Paste ink, commonly used in letterpress and lithographic processes, has high viscosity, evaporates slowly, and has high pigment density; liquid ink, used in flexographic and gravure processes, is thin, quick-drying, and holds less pigment; screen ink, used in screen printing, is thicker than paste ink.

Also see printing ink solvent, printing processes, tack.