Spotone inks and ooooo high quality artist's brushes. A small porcelain or glass dish. Place a few drops of each ink on the dish and let them dry. They can be mixed to make different tones. Have a processed photographic paper as the print to be spotted to work out the matching tone to be spotted on. Dip the brush in distilled water and pick up the ink that is closest to the area to be spotted and on the practice paper lightly dot until there is a match then apply to the print. Take your time and practice on reject prints. It's better to be additive than to do too much. Carefully remove dust on negatives before printing so spotting can be kept at a minimum. Practice, practice,practice -- don't ruin a print you have spent a lot of time on to begin with. Spotting is not difficult if you take your time.

http://www.jeffreyglasser.com/