Platinotype is a monochrome photographic printing process, based on the light-sensitivity of Ferric oxalate.

Ferric oxalate is reduced to ferrous oxalate by light. The ferrous oxalate then reacts with platinum (II) (or palladium II) reducing it to basic platinum, which builds up the image.

William Willis discovered the process in 1873 and the first platinum paper reached the market in 1881, produced by the Platinotype Company, a firm founded by Willis in 1879.

When Willis invented the process, platinum was relatively cheap, but it quickly became more costly starting in 1906. In 1907 platinum had become 52 times more expensive than silver. Eastman Kodak and most other producers stopped fabrication of the paper in 1916. Russia controlled 90% of the world platinum supply in World War I and all available platinum was used in the war effort.

Due to the shortage of commercial paper and high cost, photographers experimented with palladium paper and platinum-palladium mixes. Platinum paper has continued in use until the present, interrupted only by the world wars.

Due to the unavailability of pre-coated sensitized paper, all platinum/palladium (Pt/Pd)printing is done on paper coated by the printer. The light sensitive chemicals are mixed from powdered basic chemicals, or some commerciually available solutions, then hand applied with a brush or a cylindrical "pusher". Many artists achieve varying effects by choosing different papers for different surface charactarisitcs, including vellum, rag, rice, among others - even silk. On the collecting market, Pt/Pd photographic prints often sell for many times what a similar silver gelatine print would sell for.

By varying the amoint of Pt vs Pd and the addition of oxidizing chemicals such as hydrogen peroxide and potassium dichromate or potassium chlorate, the contrast and "colour" of the final image can be modified. Because of the non-uniformity of the coating and mixing phases of the process, no two prints are exaclty the same, adding additional "cache" to a Pt/Pd print. The inherent low sensitivity of the process is due to the fact that the ferric oxalate is sensitive to ultra-violet light only, thus specialized light sources must be used and exposure times are many times greater than those used in silver-based photographic processes.

Characteristics

• An absolutely non-reflective surface of the prints, compared to modern-day glossy prints
• Very delicate, large tonal range
• The prints, not being coated with gelatin, do not exhibit the tendency to curl
• The darkest possible tones in the prints are still lighter than silver-based prints. Recent studies have this attributed to an optical illusion produced by the gelatin coating on RC and Fibre Based papers. Platinotypes which have been waxed or varnished will produce images that appear to have greater D-max than silver prints.
• Very stable process, platinum prints are far less succeptible to deterioration than silver-based prints because they are commonly printed on 100% rag papers

See also: Palladiotype, Photographic processes

Photographic processes | Платиновая печать