The cyanotype process was developed in 1842 as a 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 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.
One of the main uses of sun printing was for botanical prints, used by botanists exploring the West to record their finds for posterity; many of these botanical sun prints are now in museum collections. Sun printing fell out of practical use when replaced as a photography process by silver based photography, and replaced as a copying process by mimeography and xerography. But today it is enjoying a revival as an art form.
To make a sunprint today, you can order the treated photographic paper online, at www.lawrencehallofscience.org. Collect and place objects with a distinct shape on the special print paper. Make sure not to expose the paper to the sun until the objects are in place. Leave the paper with the objects on it in the sun for 2-5 minutes. You will know the print is done when the exposed paper turns almost white. Quickly take off the objects from the paper, making sure the paper is not exposed to sunlight. Then, place the paper in water. This stops the chemicals from reacting to the sunlight. The background will turn blue while the shadow of the object turns white.
