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The cyanotype process
was developed in 1842 as a non-silver, photographic method to produce
or duplicate images. Cyanotypes or sun prints make use of two
photosensitive chemicals (ferric ammonium citrate and potassium
ferricyanide) that become fixed and insoluble when exposed to
ultraviolet light. A dried, pressed leaf or flat piece of lace is laid
on a sheet of paper or cloth treated with the chemical emulsion. It is
then exposed to light from the sun or a sun lamp for several minutes.
Following exposure the paper is washed in water to remove all the
unexposed emulsion. When exposed to air a white silhouette-like image
appears on a Prussian blue background. If necessary, the blue color
can be intensified by placing the print in a solution of hydrogen
peroxide. Once dry, the paper is light sensitive and will fade over
time.
In addition to
blueprints a diversity of other chemical compounds can be used to
produce yellow, gray, brown, black or other background colors. The
underlying color of the paper or cloth determines the color of the
lighter silhouette image.
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