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.
Fixing The Prints. It is advisable to prepare the hypo bath by hydrometer test, making it 18 grs. strong. The hypo should also be slightly alkaline and be tested with blue and red litmus paper. If the red litmus paper turns blue the bath is, of course, alkaline, but, if blue litmus paper turns red it will be necessary to add a few drops of saturated solution of carbonate of soda or borax until the red litmus paper turns blue. This bath can be used in any quantity but it is advisable to use plenty of solution in order that the prints may be more easily handled and moved about, thus insuring thorough fixing. Should more or less bath be used, always be careful that the proportions remain the same.
203. Where large batches of prints are toned there is danger of carrying some of the prints a little farther, or under toning them in the gold bath, the result being that when they come from the platinum bath a difference is noticable in tone. As some will be warmer than others, before fixing, in order to equalize the tone, place them in a sulphite of soda bath as follows: To 60 oz. water add 1/2 oz. saturated solution sulphite of soda. This will darken the tone somewhat, imparting to all prints a uniform color.
Prints should be placed in this bath a dozen at a time, handled over for half a minute and then put directly into the fixing bath, always picking them over and over, face down. Handle them exactly as other prints are treated during fixing. Allow them to remain in the bath for 15 minutes, keeping them in motion until fixed.
Using Baths More Than Once. The gold bath should be saved and the clear liquid used for your next toning. The platinum bath can also be used over. As the platinum bath is extremely acid, never use more than one-third new to one-half old bath. If you were to use the entire old bath the platinum would be exhausted, the acid still remaining in it. By adding fresh platinum solution to the old bath, the proportion of acid would become too great and there would be danger of cutting out the highlights of your prints. For this reason, use only a part of the old bath. One-third old with two-thirds fresh bath added, makes richer tones than a fresh bath, and obviates all danger of bleaching the prints. Toning too slowly in the platinum flattens the whites and tends to cause muddy shadows.
Final Washing. After the prints come from the hypo and have been placed in the salt bath for 5 minutes (4 ozs. of salt to 1 gal. of water, as mentioned in the general instructions given in the preceding chapter), they should be thoroughly washed by hand in at least three changes of water, in order to keep the prints constantly separated before placing them in running water, or in a washing tank. By doing this the surface hypo will be washed off and small air bubbles removed. These air bubbles sometimes fasten themselves on the prints and hold the hypo under them, which permits the hypo to bleach, causing small white spots to show on the prints when they come from the wash water. After washing the prints by hand in two changes of water, one hour in running water will be sufficient additional washing, providing the prints are thoroughly separated every five minutes. Ten to twelve changes by hand, however, will prove far better.
When washed by hand the prints should remain in each water about 5 minutes and also be separated several times in each change of water.