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.
Sulphite Of Soda Bath. To 60 ounces of water add 1/2 ounce saturated solution of sulphite of soda. This bath will darken the tone somewhat but all prints will be of a uniform color when coming from this bath. Prints should be placed in this bath a dozen at a time. Handle over for half a minute, or until they become a uniform color and then place directly into the fixing bath, picking them over and over, turning face down. Handle exactly as you would other prints, allowing them to remain in the hypo bath for 15 minutes, keeping them constantly in motion during the fixing.
Hypo Bath. The hypo bath should be prepared according to formula given in Brief General Instruction, should be tested with litmus paper, and must be neutral or slightly alkaline. If it tests acid, neutralize it by adding a dram, or more, if necessary, of the borax solution. When the red litmus paper turns blue, you will know that the bath is alkaline. Be careful, however, that the matter is not overdone by making the hypo bath too strongly alkaline, as a neutral bath will do no harm and will work satisfactorily.
This bath can be made up in any quantity. It is advisable, however, to use plenty of solution. If more or less bath is used be careful that the proper strength is retained. To repeat a caution: It is advisable to prepare this bath by hydrometer test, as you will then be more sure of uniform results.
Salt Bath. After prints are fixed they should be transferred to a salt bath, prepared as follows: Four ounces of salt to every gallon of water. Use plenty of solution, but always keep the solution the same strength. Allow prints to remain in this bath for 5 minutes, picking them over and over.
Final Washing. The final washing is more important with collodio carbon than any other paper, owing to the weight and thickness of the stock. Prints should be carefully washed through 12 to 15 changes of clear water, handling each print separately, after which they may be laid out to dry.
Drying Collodio Carbon Prints. Collodio carbon prints can be dried flat by the following method: Lay all the prints out on a sheet of glass, face down (being certain that the glass is perfectly clean). Have one overlap the other a trifle. After all are on the glass, lay a sheet of clean blotting paper over the prints, and then with a print roller carefully roll over the blotter and expel all surplus water. Next take each print separately and place between clean, dry blotters, lay a sheet of glass on the top and weight it down. You will, of course, see the necessity of laying these blotters on a perfectly level surface. Allow the prints to remain in these blotters for one hour; then change to dry blotters, allowing them to remain for another half hour, after which for final drying, change again to dry blotters and plain cardboard.