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.
Borax. Borax is found native in the crude state in the saline portions of Nevada and California, but is also manufactured by boiling boracic acid (crude) with sodium carbonate. It is put up both in crystal and powder form. We advise the use of the crystals, as there is less danger of adulteration. It is colorless. As it dissolves slowly in cold water, hot water should be employed for the purpose.
Acetate Of Soda. A colorless crystal. Also obtainable in granular form. Dissolves readily in water. If exposed to heat or air it loses its water of crystalization rapidly and becomes a white powder. When in powder form it is twice as strong as the crystals. It is used in the toning bath for preventing the highlights from bleaching. It is a very slightly alkaline chemical. When added to water it requires hours for the solution to become noticeably alkaline.
Hyposulphite Of Soda. (Thiosulphate of Soda). Commonly called "hypo." Is put up in crystal and granular form. Colorless. From this you prepare your fixing bath. The action on the prints is identically the same as on the plates, as it dissolves all the free silver which has not been eliminated in the washing and toning baths.
55. The chemicals employed in toning may be divided into two principal classes - acids and alkalies. Both must be used in preparing the toning bath, but it makes a great deal of difference which is in the greater proportion. If proportions of acid and alkali are equal the bath is said to be neutral. It will give fair results in this condition, but as it never should be used to tone in an acid condition, it is safer to make it slightly alkali. To test the bath for this use litmus paper, which is of two colors, red and blue. Red litmus paper coming in contact with an alkaline bath will turn blue, while blue litmus paper coming in contact with acid turns red. A neutral bath will have no effect on either red or blue litmus paper.
Litmus Paper. The best litmus paper to use for testing your gold bath is that put up in small glass vials, and a small bottle will last a long time. You should have a bottle of blue as well as one of red litmus, for should your bath become acid from continuous use you can test it with blue litmus paper. The preservative which is used by the paper manufacturers in preparing the paper, and which may not be entirely eliminated with the wash waters, is apt to turn the bath acid after quite a few prints have been toned. It is well to keep a piece of blue and red litmus paper in the bath while toning, and watch them carefully.
As soon as you notice the slightest change take immediate steps to have the bath test properly.
57. It will require about two minutes for the red litmus paper to turn blue after having added the borax, or Solution No. 3. If the small quantity of Solution No. 3 you have added does not perform the work in the given time, add more borax solution and continue to add until the litmus paper does turn blue.
58. The fresher the paper the more preserving chemical it contains; therefore, you require so much more of your Solution No. 3 than you would for old paper, while with old paper you will require more of the gold or Solution No. 1, owing to the fact that old paper requires a stronger gold solution when toning than fresh paper, but it does not require as much alkali, as the paper contains less acid. The amount of gold given in the formula is the minimum that should be usd for toning. You may find it necessary to use a trifle more, and in this you will be governed by the speed of your toning bath. It is not advisable to tone too quickly or too fast, as tones produced by fast toning are generally only surface tones, and when the prints enter the hypo the tones change considerably. Usually about six to eight minutes is required to completely tone a print.
59. Before printing any paper notice whether it is old or fresh. If it is old you will find that the paper will be slightly discolored either around the edges on the surface or on the back. Should you be compelled to print from both old and new, separate them, toning the old paper first and the new last. The reason you tone the old paper first is because your bath is fresh and crisp and the old paper needs crisping a trifle, which it will receive in a fresh bath. After your old paper is toned your bath is in better condition to tone fresh paper, because it will contain a certain amount of free silver, which ripens the bath, and your fresh paper will not tone quite so quickly but much more evenly than it would in a fresh bath.
60. We caution you again on the condition of your bath. It is absolutely necessary that the bath be not too alkaline, and must never be acid, but should lean a little over the neutral point to a slightly alkaline condition. A bath too alkaline will give muddy whites. A bath that turns red litmus paper blue in from one to two minutes is just right.