Any of a variety of water-soluble, resinous plant or tree exudations used in the formulation of printing inks and varnishes, in particular gum arabic or gum tragacanth. Gums are also used in offset lithography, both in the production of printing plates and in press fountain solutions as a means of desensitizing the non-image areas of the plates and keeping them ink-repellent. (See Fountain Solution.) So-called synthetic gums are also used as plate gum and as desensitiser in fountain solution. Synthetic gums - made from plant material such as cellulose and starch - include carboxymethyl cellulose and dextrin.