Cyanotype Process: How It Works

Cyanotype is a contact printing process that produces images in Prussian blue. It's one of the oldest photographic processes still in active use, and one of the most forgiving to learn.

What draws me to cyanotype isn't the blue — it's the directness. Coat, expose, wash. The process gets out of the way and lets the image do the work. When people first start working with historic print processes, they often start with cyanotype because it’s simple and straightforward.

The chemistry is simple. Two solutions, mixed fresh before each session:

• Solution A — ferric ammonium citrate, the light-sensitive component. It reacts to UV exposure.

• Solution B — potassium ferricyanide, which produces the characteristic Prussian blue through its reaction with the iron salts. It carries some UV sensitivity of its own, though less than Solution A.

Each solution is prepared separately and can be stored for months in amber bottles, away from light. Once combined in equal parts, the working solution is good for a few hours. So it’s best if you only mix what you need, right before you coat.

The coated surface is dried in the dark, exposed to UV light through a negative, then washed in water. That's it. No fixer, no stop bath. The blue deepens as it dries and oxidizes over the following day.

How I use it

I use cyanotype in my own work both as a standalone process and as a layer over other prints. For example, coating cyanotype over a selenium-toned kallitype to build depth and color that neither process could produce alone. You can see this in pieces like Drapes and across much of my still life work.