A Historical Perspective
William Willis invented and patented the Platinotype processes in 1879. By the 1930's the commercial availability of platinotype paper had come to an end. During this period of time photographers had marveled at the ability of platinum to record fine detail and subtle to dynamic tonal ranges. Platinum printing became the choice of many photographers of that time period, P.H. Emerson, Frederick Evans, Laura Gilpin, Gerttude Kasebier, Paul Strand, Alfred Stieglitz, and Edward Weston were printing with platinum materials. With the out break of the First World War creating a shortage of platinum materials. Many companies ceased the manufacturing of platinum paper including Eastman Kodak in 1916 and the Platinotype Company of England the last paper maker stopped production in the mid 30's. Now the only method left to photographers was to coat their own papers just as we do today.
The Platinum/Palladium Print
Most people think that printing platinum and palladium is done with precious metals, but actually we are nothing more than Iron printers. Iron salts in the emulsion coating of the paper form the light sensitive materials. Platinum replaces the iron during the processing of the print. The metal salts in the printing process are Potassium chlorplatinite and Sodium chloropalladite. These metals can not be told apart in the resulting prints. Changes in temperature and type of developer renders Platinum normally a cool black tone to warm and Palladium as a warm tone to cold. The exposure times can be long, some prints taking 30 to 45 minutes. The processes is not the type of thing that you can do with your enlarger. The coated material is only sensitive to the UV range of light. Contact printing is in order. Most of the coating and processing can be done under subdued tungsten room light. Just think making prints with out a darkroom!