The best formula for Amidol is, from all reports, the Michael Smith formula since it doesn't live up to Amidol's normal reputation of a short "use" life. I have found that the water bath in conjunction with Amidol gives a fair amount of flexibility in achieving proper print contrast. I use Amidol with Azo and the only toning that I have personal experience with is with highly dilute selenium. (primarily for archival purposes).