This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
Toning Bath Becoming Discolored When First Prepared. This will only occur if the toning bath has been made up in a tin, or in any metal dish. Whenever a metal dish is used a chemical action sets in, more especially in tin, which will discolor the toning bath and make it useless. Moral - never use metal trays for any purpose in photography.
Milky Color Of Bath After Toning A Number Of Prints. - The bath will become somewhat milky with use, which does no harm if its chemical strength is not exhausted. After a number of prints have been toned and the bath is allowed to stand, it will discolor as the light acts on the silver released from the prints. As long as the prints are clear and crisp it matters little; if the prints look muddy, use a fresh bath.
Straight Lines On Toned Prints. This will only occur when the prints are allowed to lie in the baths without picking them over. Gelatin prints, when wet, will sink to the bottom of the tray and stick together. Where one print laps over the other the silver in the print oozes out of the edge of the print and leaves a mark.
Weak Prints. If the toning bath is too cold, or the prints are not printed dark enough, the result will be weak prints.
Softening Of Prints While Washing Or Toning. This is generally caused when the toning bath becomes too warm. Carefully watch the temperature of the bath. If the rinsing waters are too warm they soften the prints. At the slightest sign of softening of the prints, prepare a very weak solution of alum, as follows: To one-half ounce of saturated solution of alum add sixteen ounces of water. Of this solution add just a little to the water and it will harden the surface of the prints. Thoroughly wash the prints after applying the alum bath, to eliminate all the alum.
Prints Continue To Tone In Water Previous To After-Fixing Bath. If you are not using enough water in your tray the toning bath which you are carrying with your prints into this water will cause it to become a weak toning bath and the prints will continue to tone. If you are toning very many prints change the water occasionally, thus eliminating all the toning solution.