Platinum print

The platinum print ( platinum print ) is a photographic gem printing method that William Willis invented in 1873 and patented in 1878. The method was particularly popular with the pictorialists 1880-1914.

Method

The platinum printing process based on the 1832 discovered by John Herschel light sensitivity of Platinchlorürs. An implementation of this sensitivity to light in a photographic process, as the production of a light-stable light image, but only succeeded Willis in 1873.

For the platinum print a paper with oxalic acid, iron (III ) chloride and platinous is ( new name: potassium tetrachloroplatinate ) and dried. The dried sheet can then be exposed through a negative. The result is a faint image of which strongly emerges by immersion in a hot, aqueous solution of potassium oxalate and a small amount of platinum salt. After repeated washing and washing in a solution of potash and potassium oxalate the final positive image can be dried.

On exposure the iron chloride oxalate is reduced by the presence of the platinum salt to ferrous oxide, which then reduces the platinous. In the development of the iron chloride, to which attaches the platinum compound. When washing is platinum deposited continuously and with soft Tonwertübergängen onto the paper. The images are chemically almost immutable and therefore very durable. The image is not embedded in a colloid layer, but directly into the paper fiber. The tonal range is very good and the images have good depths. The method has been used particularly in the challenging portrait photography. Additions of gold, uranium and silver allowed a variation of the tint.

Willis produced in his London-based company finished groomed and dried papers. Due to a strong increase of the required platinum compound before the First World War, the method of insignificance sank.