Prints made in the precious metals of Platinum, Palladium or Silver.
A solution containing Platinum and Palladium salts is brushed onto a cotton rag paper in subdued light. A negative the same size as the final print is then placed directly onto the dried coated paper and a piece of glass is used to keep the negative in contact with the paper.
During exposure to sunlight or an ultra violet light source a reaction takes place resulting in the final image of pure platinum and palladium being trapped in the surface fibers of the paper. The print is then cleared and washed to remove by products from the chemical reactions and dried.
Colour and contrast can be controlled to range from warm dark browns to cold neutral blacks depending on the proportions of the metals used and the humidity of the paper during exposure.
The Platinum and Palladium process first used in the late 19th century is one of the most stable and archival of all printing processes in photography. When framed and cared for correctly the prints will last for a millennium.
Kallitype prints preceded the use of the platinum process and use silver nitrate instead of the platinum or palladium salts and employ a developer solution after exposure to render the final image of pure silver in the surface fibers of the paper.
In both of these manual printing processes results are never guaranteed and serendipity is always close by, making for a unique hand made.