A substance mixed with pigment, it holds raw pigment in such a way that it becomes workable in a painting medium. Its purpose is to weld the pigment granules into some sort of shape---liquid, semi-liquid or solid---where brush, knife or hands can carry the color to the canvas or paper. In oil paint, raw pigment is usually combined with a linseed oil binder to form a fluid paint. Watercolor&#39;s binder is gum Arabic, and pastel is bound with gum tragacanth. Joe Singer writes in his book, "How to Paint Portraits in Pastel" that &#39;it is often the binder and not the pigment that is the main cause for the deterioration of paintings, especially oil.&#39; Source: Roger Dunbier, PhD, Unpublished essay on Mediums. <br><br>The nonvolatile adhesive liquid portion of a paint that attaches pigment particles and the paint film as a whole to the support.<br><br>That which holds the paint together, such as linseed oil for oil painting, polymers for acrylics, gum arabic for watercolors and gouache.<br><br>The ingredient in the vehicle of a paint which adheres the pigment particles to one another and to the ground. It creates uniform consistency, solidity, and cohesion.Also see adhesive, adobe, mortar and pestle, polymer clay, and solvent.