G E H L I M A G I N G

Alternative Photo Processes

Platinum is a process in which the image is formed of metallic platinum, as opposed to gelatin silver in which the image is composed of metallic silver. Another difference is that a gelatin silver image is suspended in an coating (emulsion) on the paper whereas a platinum image is actually in the surface of the paper. The paper is sensitized by brushing with a mixture of ferric oxalate and potassium chloroplatinite. It is then contact printed using ultraviolet light. Exposure to ultraviolet light changes the ferric oxalate to ferrous oxalate in direct proportion to the amount of light reaching the paper. Development in potassium oxalate changes the platinum to a metallic state and dissolves the ferrous oxalate. Clearing in a dilute acid dissolves any remaining ferric oxalate. Platinum prints are second only to gum prints in permanence.