is a solvent or oil used to solubilize, or disperse, resins, pigments, and additives in ink formulations; also used to adjust ink viscosity and drying characteristics. Selection of an ink solvent is based primarily on boiling range, viscosity, solvency, and molecular type (i.e., paraffinic, naphthenic). The solvent can range from a light, low-boiling material (e.g., toluene) to heavy asphaltic material (commonly referred to as carbon black wetters). Important qualities in an ink solvent include dilutabilty (ability to hold a resin in suspension), good tack rise characteristics (control of ink stickiness), and low toxicity. An ink solvent that boils above 600°F is commonly referred to as an ink oil.

Also see printing ink, printing processes, tack.