Overview
Platinum and palladium printing (often combined as "Pt/Pd") is widely considered the finest photographic printing process for monochrome images. The image is formed from metallic platinum or palladium embedded in the paper fibers, rather than sitting on top as with silver gelatin prints. This produces an extraordinarily long tonal scale, beautiful matte surface, and exceptional archival permanence: platinum prints can last thousands of years without fading.
The Chemistry
The sensitizer consists of ferric oxalate (the light-sensitive component) and a platinum or palladium salt (potassium chloroplatinite, sodium chloropalladite, or a combination). A contrast agent (typically potassium chlorate or hydrogen peroxide) is added to control the contrast of the print. The ratio of platinum to palladium affects image tone: pure platinum gives a cool neutral gray, pure palladium yields a warmer brown-black, and mixtures fall between.
Printing Process
Coat high-quality 100% cotton rag paper (such as Arches Platine or Hahnemuhle Platinum Rag) with the sensitizer using a brush or glass rod. Dry the coated paper, then contact print with a large negative under UV light. Exposure times range from 3-15 minutes depending on the UV source and sensitizer formula. The image appears during exposure as a faint grayish-brown.
Development and Clearing
Develop the exposed print by immersing it in a tray of potassium oxalate developer. The image snaps to full density within seconds: this is one of the most dramatic moments in any darkroom process. After development, clear the print in three successive baths of dilute hydrochloric acid or citric acid to remove unexposed iron salts. Finally, wash thoroughly in running water and hang to dry.
Practical Considerations
Platinum/palladium printing requires large negatives (contact printing only), so photographers typically work with large format cameras (4x5, 5x7, 8x10) or create enlarged digital negatives from smaller formats. The cost of noble metals makes each print expensive, so careful testing and note-keeping are essential. Despite the cost and complexity, the unmatched tonal beauty and permanence of Pt/Pd prints make the process deeply rewarding for fine art photographers.
