A type of ink vehicle—the fluid carrier of the ink pigment—that dries by precipitation of the pigment out of the vehicle, rather than by absorption of the vehicle into the substrate or by oxidation of the vehicle. Also called moisture-set inks, glycol vehicle inks are made from water-insoluble resins that are dissolved in glycol (an alcohol also used in antifreeze). Glycol itself is water-soluble, and when moisture comes in contact with this type of vehicle, the glycol is dissolved, and the resin precipitates out, dragging the pigment with it. A variation on the glycol vehicle inks are fast-drying inks, which neutralize an acidic resin with an amine and dissolve the resulting resin salt in glycol. When printed, the amine is absorbed into the paper, de-neutralizing the resin, which is abruptly rendered insoluble in glycol and precipitates out and hardens on the surface of the substrate. The hardening of the resin happens very quickly, and without the use of moisture. Glycol vehicles are commonly used in letterpress printing. (See Vehicle.)
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