Cyanotype printing is one of the earliest forms of printing process. An emulsion is applied to the surface of the paper, a photographic negative is placed on the surface and then exposed to UV light. They can be placed in the sun, or under a hydroponic grow lamp, which I use. The print is then rinsed in running water for about 15 minutes then dried. It can then either be left the original blue, or placed in a toning bath. Some common toners used are tea, coffee and oak bark.