The rather simple process involved using 2 chemicals
1) Ammonium iron (III) citrate and
2) Potassium ferricyanide
A solution of these 2 chemicals would be poured over any substance capable of retaining the iron solution, typically this meant using watercolour paper. The paper would then be allowed to dry, and when dried became ready for exposure. Ideal subjects for cyanotype photography were flat objects that could simply be placed on top of the treated paper, weighted down with glass, and left out in the sun to expose for 10-20 minutes. After the paper has turned noticably blue-grey, the paper would then be washed in water to remove the unreacted iron solution and then left to dry, and the print was then complete.
The primary advantage of cyanotype was its ease and simplicity, which made it ideal for making multiple copies of a subject. Engineers made significant use of this process to make large copies of plans, and the aptly named "blueprint" was born.

Algae - Anna Atkins 1843
References
- Wikipedia 2009, Cyanotype, viewed 6 August 2009 http://en.wikipedia.org/wiki/Cyanotype
- Wikipedia 2009, John Herschel, viewed 6 August 2009 http://en.wikipedia.org/wiki/John_Herschel
- Photography.com 2009, Cyanotype, viewed 6 August 2009 http://www.photography.com/articles/history/cyanotype/







