The platinum print, also called a platinotype, is a form of contact print formed when platinum is brushed unto a sheet of paper. They contain a matte finish and possess a great tonal range, therefore more desirable to photographers who are more focused on the more aesthetic side of photography.
While the first patent was granted for the process in 1873 to William Willis, the reaction of light on platinum has been observed as early as the 1830s. However, research and interest on the process waned as more commercially-viable photographic processes became available back then.
As mentioned, one great hint in determining if an image is a platinum print is the brush strokes that surround the image. In order to produce the image, a negative is placed in contact with the sensitized paper and is exposed under the sun. After exposure, the photo is taken back inside and is doused with developer.
Platinum prints are also known for their longevity — platinum is very stable against chemical reactions that might degrade the print. It is estimated that a platinum image, properly made, can last thousands of years.
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