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.
Note (B). Only pure water, testing neutral with litmus paper, should be used for making a salt bath for self-toning paper. Water containing alkali will not give the best results. Distilled or ice water may be used with excellent results.
Note (C). Be careful to use a sufficient quantity of salt bath for the number of prints. Prints should be kept in the salt bath only until the desired tone is reached, whether it be two or ten minutes. Remember, the salt solution is nominally the toning bath, and prints should be handled in this the same as in the other toning baths. One quart of salt water is sufficient for two dozen 4x5 prints or their equivalent.
Note (D). Different amounts of salt give various tones on this paper. For older paper use more salt; one and one-half to two ounces of salt to 64 ounces of water.
Note (E). After prints come from carbonate of soda bath they can be washed in one clear water and then flattened for five minutes, when they will lie flat in the hypo bath and not curl. Care must be taken to keep the prints flat during toning and fixing.
Note (G). If prints show blisters after hypo bath, they should be put in a salt water bath for from five to ten minutes; salt, four ounces; water, one gallon.
Note (I). Yellow stains are caused by too weak a salt bath, an acid fixing bath, or allowing prints to adhere to one another when first placed in the hypo bath. Great care must be taken to separate prints when they first go into the hypo bath, or yellow stains may appear, which no after fixing will remove.
Note (J). In handling Self-Toning paper, should trouble come from chipping or cracking of the collodion film, it is caused by prints being allowed to curl during the manipulation. To overcome this trouble keep prints flat in the salt bath, care being taken that they are frequently separated so that the salt will have free action on their surface. After salt bath, drain them face down on the bottom of the tray for ten or fifteen minutes before putting into the hypo bath. This sets the prints in a flattened position. By handling them face up through fixing bath and final wash water, little trouble is experienced on account of tendency to curl.
530. All self-toning papers have the necessary toning ingredients in the emulsion. When the prints are placed in the water the emulsion becoming wet, the ingredients grow solvent, liberating from the paper, and when coming in contact with water form a toning bath. The action of the toning bath is similar to any other toning bath. The warmth of tone is regulated by the depth of printing, and the amount of washing previous to fixing. The purple tones are controlled by the strength of the salt bath.
Practice Work. While this process is extremely simple, yet the very best results are only obtained by practice and experimenting. The richest tones and the brightest prints are obtained by accurate printing. The tone and color of the print are governed by the strength of the salt bath. You should print a number of sheets of paper, carrying them to different depths, and observe the appearance of each print during the various manipulations. All necessary data should be noted on a few of the prints of different qualities, and these sheets should be filed in your proof file for future reference.