For several decades the use of Pyro was carried on primarily with the classic formula known as ABC Pyro. The ABC formula was used by a number of West Coast photographers, including Edward Weston and Morley Baer, and is still promoted today by Michael Smith for contact printing with AZO. It is said to be the most difficult and fickle of all pyro formulas but capable of excellent results “unequalled by even most other pyro formulas, in tonal gradation and subtle highlight separation.”