Sun printing

Sun Printing can be done through three 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.

The third, and most traditional form of sun printing, is called cyanotype. It involves exposing materials which have been treated with a solution of potassium ferricyanide and ferric ammonium citrate, to UV light, where an image is printed on the material through a chemical reaction and is set by washing with plain water. For instance, if a leaf is placed upon paper treated with this solution and left to sit out in the sun for about 10 minutes, the paper will retain the image of the leaf after it has been rinsed with water. After the paper dries, everything that was exposed to the UV rays of the sun will turn a shade of Prussian blue, while the part that was covered by the leaf will remain white.

External links

* [http://www.alternativephotography.com/process_photopolymer.html The solarplate process]
* [http://www.blueprintsonfabric.com Cyanotype Products]