Platinum print
The platinum print (platinotype) is a photographic Alternative Process , the William Willis invented in 1873 and 1878 a patent was. The process was particularly popular with the Pictorialists between 1880 and 1914.
Procedure
The platinum printing process is based on the photosensitivity of potassium tetrachloridoplatinate (K 2 [PtCl 4 ], old name: platinum chloride), which was discovered by John Herschel around 1832 . However, it was not until 1873 that Willis succeeded in converting this sensitivity to light into a photographic process, i.e. the production of a light-resistant photograph.
For the platinotype, paper is soaked with oxalic acid , iron (III) chloride and platinum chloride and dried. The dried sheet can then be exposed through a negative . The result is a faintly visible image, which becomes vivid when immersed in a hot, aqueous solution of potassium oxalate and a small amount of platinum salt. After repeated soaking and washing in a solution of potash and potassium oxalate, the finished positive image can be dried.
During exposure, the iron chloride oxalate is reduced to oxide by the presence of the platinum salt , which then reduces the platinum chloride. During development, the ferric chloride is the photosensitive substance to which the platinum compound attaches. When washed, platinum is gradually deposited on the paper with soft tone value transitions. The pictures are chemically almost unchangeable and therefore very durable. The image is not embedded in a colloid layer, but directly in the paper fiber. The tonal range is very good and the images have good depths. The process was used particularly in demanding portrait photography . Additions of gold, uranium or silver allowed the tint to be varied.
Willis produced prepared and dried papers in his London-based company. Due to a sharp rise in the price of the required platinum compound before World War I , the process sank to insignificance.
See also
literature
- Jean-Claude Gautrand : The Pictorial Techniques. In: Michel Frizot (ed.): New history of photography. Könemann, Cologne 1998, ISBN 3-8290-1327-2 , p. 300.
- Arthur von Hübl : The platinum print (= Encyclopedia of Photography. Vol. 13, ZDB -ID 1006803-x ). Knapp, Halle (Saale) 1895.
- Walter Koschatzky : The art of photography. Technology, history, masterpieces (= dtv 2898 dtv art ). Deutscher Taschenbuch-Verlag, Munich 1987, ISBN 3-423-02898-X , p. 102 f.
- Josef Pizzighelli, Arthur Hübl: The platinotype. A method for the rapid photographic production of durable copies with platinum salts. Verlag der Photographischen Correspondenz , Vienna 1882.