|Turquoise and navy and powder puff blue|
To make a cyanotype print, the paper is first treated with a sensitizer solution containing a mixture of ferric ammonium citrate and potassium ferricyanide. After drying the paper, images in the form of cut-outs, stencils, negatives, or actual objects are placed on top of the paper and exposed to ultraviolet light (sunlight works great!), which produces a blue shadow. After sufficient exposure, the paper is washed in water to remove the soluble unexposed salts. Upon drying, the image darkens as a result of slow oxidation in air. This blue pigment, known as Prussian Blue, has been used for printing ink, paint pigment, typewriter ribbon, and carbon paper. Treatment with oxidants, such as hydrogen peroxide or potassium dichromate, produces a darker blue (almost black) image.
|A cyanotype painting|