and a 20% solution of ferric ammonium citrate are mixed. The overall contrast of the sensitizer solution can be increased with the addition of about 6 drops of 1% (w/v) solution potassium dichromate for every 2 ml of sensitizer solution.

This mildly photosensitive solution is then applied to a receptive surface (such as paper or cloth) and allowed to dry in a dark place. Cyanotypes can be printed on any support capable