The chemical treatment of a lithographic plate to impart to non-image areas water-receptivity and ink-repellency, commonly achieved utilizing a solution of gum arabic or other gum compound. It is the offset press fountain solution that keeps the plate properly desensitized over the course of a print run by continually replenishing the layer of gum adhered to the aluminium non-image area of the plate. The gum's function is to attract water to the non-image. See Plate: Offset Lithography. (See also Fountain Solution.) Also called gumming.