The short read, of course, would be Ansel Adams' The Print. He covers archival toning with Selenium and a short bit on Gold, Sepia, and Polytoner. With that you can spend a few bucks and play in the darkroom. Personally I have not needed to go farther than that, but if the need arises and the temperature in the Boston darkroom is 33 F., time for a good read, and Rudman's book is the one.