Gum over platinum is a historical chemical photographic process, which was commonly used in art photography. It is a very complex process, in which a specially treated platinum print photograph is coated with washes of gum arabic, then re-exposed to the same photographic negative. The finished process results in a sepia toned print, and is said to impart added luminosity and depth. It is sometimes called "pigment over platinum". The technique is related to platinum printing.