The history of the platinum / palladium process is quite colorful but too lengthy for this space so I’ll simply describe the technique. In the platinum / palladium process (Pt / Pd), there are three primary and separate solutions that are chosen by which variation you are working with.

 ·  Platinum variation

Solution 1 - Part A: ferric oxalate

Solution 2 - Part B: ferric oxalate with potassium chlorate

Solution 3 - Part C: potassium chloroplatinite / sodium tetrachloroplatinate ( ll)

·  Palladium variation (Note: a different Part C)

Solution 1 - Part A: ferric oxalate

Solution 2 - Part B: ferric oxalate with potassium chlorate

Solution 3 - Part C: palladium (ll) chloride / sodium chloropallidite

These solutions are mixed together in a shot glass, in precise droplet based formulas, according to the quality of the negative you are printing with, to form a light-sensitive sensitizer. The droplet mixture is then gently swirled together, deposited on the paper, and brush or rod coated. Once the paper is coated, it is allowed to sit or cool air-dried. The coated paper is then placed in a hinged back contact printer, along with your negative, and exposed to UV light.

During the exposure, a chemical reaction occurs that converts the ferric salts in the formula to a ferrous state. This image, unlike other iron-based processes, cannot be evaluated easily in a printing-out manner and is generally ready for development when a “whisper-image” of your anticipated print is seen. Following the exposure, the exposed paper is developed in one of many developers, such as ammonium citrate or potassium oxalate, where it is instantly reduced to a metallic platinum, or palladium, state to the degree that the negative has permitted exposure. At first, the image you will see is iron based but will convert to platinum or palladium metal in the developer. The developed print is then cleared in an acid bath sequence, i.e., EDTA, to remove any unexposed iron ferric salts, leaving a print made entirely of platinum or palladium. The print is then washed for permanence.

The Pt / Pd process has a potentially long tonal range, which many practitioners feel is significantly able to render values well beyond the ability of a traditional silver gelatin paper. It is also able to provide incredible depth and detail in the shadows. These very long tonal ranges, regardless of lengthy exposure times, are partially the result of an odd exposure characteristic called “self masking” that occurs in most POP iron-based processes. Self-masking is a term that describes what happens during long exposures when light continues to expose highlights after the shadows have reached an optimal degree of exposure.