In a cyanotype, a blue is usually the desired color; however, there are a variety of effects that can be achieved. These fall into three categories: reducing, intensifying and toning.
Reducing is the process of reducing the intensity of the blue. Sodium carbonate, ammonia, Clorox, TSP, borax, Dektol and other reagents can be used to do this. A good easily obtained reducer is Sunlight laundry detergent. When using a reducer 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.
Intensifying is the strengthening of the blue effect. These reagents can also be used to expedite the oxidation process the cyanotype undergoes. These reagents are hydrogen peroxide, citric acid, lemon juice, and vinegar.
Toning is the process used to change the color of the iron in the print cyanotype. The colour change varies with the reagent used. There are a variety of elements that can be used, including tannic acid, oolong tea, wine, cat urine, and pyrogallic acid.