3 THE PLATINUM AND PALLADIUM PROCESS

The platinum process was patented and introduced to the marketplace under the name Platinotype by the Englishman William Willis in 1873. One of its earliest and most skilled practitioners was Peter Henry Emerson, who was much admired by Stieglitz for his efforts on behalf of photography as an art form and who in 1887 awarded Stieglitz the first of his many medals and prizes in photography. Emerson expressed his admiration for the platinum process in his textbook, Naturalistic Photography (Emerson 1899, 135–36):

Every photographer who has the good and advancement of photography at heart, should feel indebted to Mr. Willis for placing within his power a process by which he is able to produce work comparable, on artistic ground, with any other black-and-white process. We have no hesitation in saying that the discovery and subsequent practice of the process has had an incalculable amount of influence in raising the standard of photography.

Making a platinum or palladium print involves the sensitization of paper with ferric oxalate and platinum or palladium chloride. Light exposure reduces the ferric salts, and the exposed paper is then immersed in potassium oxalate, which catalyzes the reduction of the platinum or palladium salts to the final metallic image material. Unwanted iron salts remain in the paper, however, and must be eliminated by several baths in dilute hydrochloric acid and a final water wash. (For more detailed information on the chemistry of the platinum and palladium process, see Gottlieb 1993, 1995.)

The resulting print is made up of finely divided metallic platinum or palladium embedded in the fibers of the paper surface. That surface is completely matte and can therefore be viewed from any angle, as there is no emulsion or subsequent gloss. A variety of papers can be used, and contrast can be varied by dilutions of the sensitizer and other manipulations (Reinhold 1991). But the primary advantage of the platinum or palladium process in comparison to the silver process, which preceded and succeeded it, is that it can reproduce a much longer tonal scale. A full-scale platinum or palladium print from a properly rendered negative has an unmatched tonal beauty.

Platinum and palladium have been described here interchangeably because both are based on the light sensitivity of iron salts, and the printing and processing procedures are nearly identical. They can even be mixed together in the same sensitizer. However, there are some differences between the two metals that are of considerable significance for this investigation.

While palladium appears in Willis's original patent specifications (Willis 1880), it was not widely used until 1916 when the British government forbade the use of platinum for photography because it was needed for the war effort. In June 1916 the Eastman Kodak Company also ceased production of the platinum paper it had manufactured since 1906. As photographers like Stieglitz began, of necessity, to rely more heavily on the substitute palladium papers, certain differences became apparent. Most important, palladium prints were inherently warmer in tone than platinum. Although color could be altered by reducing developer temperature or by using toners such as lead oxalate, it was extremely difficult to produce the same neutral gray tones with palladium as were naturally rendered by platinum. Palladium prints also had somewhat lower contrast, although that could be compensated for by adjustments to the sensitizer solution or the developer dilution. Moreover, unlike platinum, palladium is slightly soluble in hydrochloric acid, which is the clearing bath for the process. Therefore, a more dilute clearing solution, perhaps 1:200 rather than 1:60, was recommended for palladium.

Until recently, both platinum and palladium prints have had an excellent reputation for stability and permanence, primarily because the metallic platinum or palladium that forms the image is more resistant than silver to attack from peroxides and other oxidants. However, acidity introduced by the clearing bath can threaten the paper support, and it now appears that palladium prints in particular may be more prone to staining or discoloration than was previously expected.