tack - in printing inks, ink particle cohesion that resists separation on the rollers of a press. Inks generally exhibit tack rise (i.e., increased stickiness) during printing, which can result in splitting or picking (surface removal) of the paper. Tack rise can be controlled to desired levels by adding solvents with different boiling characteristics and of different molecular types. Isoparaffins and normal paraffins impart very low tack rise; naphthenics, intermediate tack rise; and aromatics, high tack rise. Tack can be measured with an inkometer in terms of the torque developed by a system of rotating ink-wet rollers. See printing processes, printing ink solvent.