As the name suggests, this process of photographic printing gives an image a cyan blue tint. This simple and low cost process was popular among engineers in the 20th century as they could create large scale copies of their work, the blueprints. Anna Atkins, one of the first female photographers to bring this process into photography, combined it with the process of photograms to create a limited series of cyanotype books on ferns and other plant life.
Resident artist Uzma will be learning and practicing this process during the course of the residency.
Equal volumes of an 8.1% solution of potassium ferrycyanide and a 20% solution of ferric ammonium citrate are mixed typically. This mild photosensitive solution is then coated on a receptive surface like paper or cloth and allowed to dry in a dark space. Any surface like watercolor paper (ideally), cotton, wool and others, that can soak up the iron solution are suitable for this process.
Avoid alkaline buffered papers as it may cause degradation of the image over time.
The positive image can be produced by exposing to a source of UV light (sunlight) with a negative or using the method of photograms. The UV light reduces the iron(III) to iron(II). Followed by a complex reaction of the iron(II) complex with ferricyanide. Result : an insoluble, blue dye (ferric ferrocyanide) known as the Prussian Blue.
Developing the image requires washing of the yellow unreacted iron solution under running water. The blue color intensifies upon drying. This can be further speedened by soaking the print in a 6%(v/v) solution of 3%(household) hydrogen peroxide. The insoluble Prussian Blue is all that remains after. For the solution which is created for coating the surface, if you need more contrast, simply add 6 drops of 1% (w/v) solution potassium dichromate for every 2 ml of sensitizer solution.
Reducing – It is the process of reducing the intensity of the blue by using Sodium carbonate, ammonia, Clorox, TSP, borax, Dektol and other reagents. It is important to pull the cyanotype out of the weak solution and put the cyanotype into a water bath to arrest the bleaching process while reducing.
Intensifying – In order to intensify the blue, Hydrogen Peroxide, Citric Acid, Lemon Juice, and Vinegar, are some of the reagents that can be used to expedite the oxidation process.
Toning – The process of changing the color of iron in the print. Color changes vary with different reagents used. Toning can be done with the use of various things like tannic acid, oolong tea, wine, cat urine, and pyrogallic acid.