Platinum print
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A platinum print or platinotype is a photographic print made by a printing process which leaves platinum metal on the surface of the paper. Platinum prints are noted for their large tonal range and for being highly stable.
Unlike the gelatin silver process, in which silver is held in a gelatin emulsion that coats the paper, platinum metal is left directly on the paper's surface or absorbed into the media. As a result, a platinum image is absolutely matte.
Platinum tones range from warm black, to reddish brown, to expanded mid-tone grays that are unobtainable in silver prints.
Platinum prints are among the most durable of all photographic processes. The platinum group metals are very stable against chemical reactions that might degrade the print—even more stable than gold. It is estimated that a platinum image can last thousands of years.
Some of the desirable characteristics of a platinum print include:
- The reflective quality of the print is much more diffuse in nature compared to glossy prints that typically have specular reflections.
- A very delicate, large tonal range.
- Not being coated with gelatin, the prints do not exhibit the tendency to curl.
- The darkest possible tones in the prints are lighter than silver-based prints. Recent studies have attributed this to an optical illusion produced by the gelatin coating on Resin Coated and fiber-based papers. However, platinotypes that have been waxed or varnished will produce images that appear to have greater maximum density than silver prints.
- A decreased susceptibility to deterioration compared to silver-based prints due to the inherent stability of the process and also because they are commonly printed on 100% cotton rag papers.
Palladium, platinum's sister element, can also be used. Many practitioners have abandoned platinum and only use palladium. The process using palladium alone (sodium tetrachloropalladate) is similar to standard processes, but rather than using ferric oxalate plus potassium chlorate as the restrainer (which is ineffective for palladium), a weak solution of sodium chloroplatinate is used instead. Sodium chloroplatinate, in contrast to potassium chlorate, does not cause grain. This formula is generally referred to as the Na2 method. This somewhat misleading abbreviation was coined by Richard Sullivan of Bostick & Sullivan, one of the principal suppliers of chemistry and printing supplies, who popularized the process.