The cyanotype process is one of the oldest photographic printing processes, discovered in 1842. It is very simple and inexpensive, using two chemicals - ferric ammonium citrate and potassium ferricyanide. These examples were made on hand-coated Stonehenge Art paper contact printed with large and medium format negatives.
Processing is done in Dihydrogen monoxide (H2O), which is fairly inexpensive and plentiful here in the eastern USA :)