Cuprotype is an under utilized alternative process invented in the 1880s by Obernetter and modernized by Jim Patterson. I am using a further, minor, modification of the modern version.
Cuprotype is properly classed as a siderotype in that it involves iron as the primary photosensitive element and couples the reduction of iron to the reduction of copper. The resulting brick-red images are composed of the pigment Hatchett’s Brown (Copper(II) ferrocyanide).
More information on my experience with this process can be found in this post from my blog. Being inexpensive and simple, I think that process deserves a more prominent place in the world of alternative photography.