Sun printing

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Sun printing can mean two different processes.

Most commonly it is a photographic process in which the final print is produced by conventional lithographic printing processes.

The process uses a film of gelatine spread on a flat and rigid surface. This is coated with a dilute solution of Potassium dichromate and dried in low light conditions. A translucent positive of the final print is secured in tight contact with the treated gelatine layer and exposed to bright sunlight for a period of up to 30 minutes. During this time the sunlight and the Potassium dichromate tan the gelatine exposed to light.

The gelatine layer is developed by washing in warm water so that the untanned gelatine is washed away. The plate is dried revealing the required design as a relief print. The surface can be inked and printed in a hand press to produce any number of identical prints of the original subject.

The other process involves the "printing-out" of a negative in contact with a sheet of black and white photographic paper and exposing it to the sun. Depending on type of paper the exposure will vary from a few minutes to a couple of hours. The paper will produce a developed image in brownish to purple hues, again depending on the paper used. The paper is then fixed and washed as in normal processing. Prints can later be toned to achieve different tones.