The Cyanotype process dates back to the 1840s. It produces a cyan-blue image, and was commonly used for photograms and blueprints in its early days.

            Cyanotypes are quite safe and easy to make with minimal chemistry needed. A solution of potassium ferricyanide and ferric ammonium citrate is needed to produce a mild photosensitive solution. This solution can coat several surfaces, most commonly paper or cloth.

            After exposure to ultraviolet light, the coated surface is soaked in water, and the unreacted iron salts are washed away. Certain reagents such as hydrogen peroxide, citric acid or vinegar can expedite the oxidation and intensify the blue.

            Many chemicals can be used to tone the image into various colors, tannic acid being a common reagent used to give the image a brown tone.

Art by Process