| Sodium phosphate | 10 | grains. | |
| Ammonium sulphocyanide | 15 | " | |
| Gold | 1 | " | |
| Water | 10 | ounces. |
The various toning baths mentioned above have one drawback common to them all in varying degrees—viz., that when once mixed and used they do not keep in good working order longer than a few hours.
7. The following bath claims to have the advantage that it will keep in working order for a short time at any rate, but the disadvantage that it cannot be used until it has been mixed twelve to twenty-four hours.
| Soda acetate | 60 | grains. | |
| Ammonium sulphocyanide | 20 | " | |
| Gold chloride | 1 | grain. | |
| Water | 12 | ounces. |
Toning should be conducted in very weak daylight, or what is much better, gas or lamplight. The latter, being practically constant, enables the operator to judge the relative colour of the prints from time to time. Care must be taken so that the prints do not stick together in the toning bath, and preferably only a few, say half-a-dozen or so, dealt with at a time, so that each print can be frequently turned over and examined. The change of colours proceeds somewhat slowly at first, but when once it begins it seems to gain in rapidity of rate of change, so that a careful watch must be kept. Let it be remembered that the print, after fixing and drying, will appear a little darker and more blue (less red) than when wet in the toning bath. The temperature of the bath must not be too cold or toning is very slow, nor too warm or the gelatine may melt and toning be uneven. From 60° to 65° F. will be found a convenient range. The prints should not be touched on their printed surface more than can be helped. The fingers must be quite clean, the solutions uncontaminated with other chemicals, and a dish set apart for toning operations only. This dish should always be washed out well with tepid or cold water before and after use, and when put away should rest flat, opening downwards, on a shelf covered with a sheet of clean blotting paper. Many failures in toning are entirely due to lack of care in details and sufficient attention to cleanliness.
When toning is judged to be carried far enough, the prints should be placed in a roomy dish containing a solution of common salt, strength one ounce to twenty or thirty ounces of water, to stop further toning.
Fixing is done with a "one in ten" solution of sodium thiosulphite—i.e., hypo. This should be prepared with tepid water, or some time before use, as the dissolving of hypo in water is accompanied by a fall of temperature. A convenient method is to place a couple of ounces of hypo in a clean pint jug, and add about half a pint of fairly warm water and stir with a glass rod until the salt is dissolved, then fill up the jug from the tap with cold water. It is highly desirable to have plenty of fixing solution, and never attempt to use the same lot twice. Place each print face down in the bath and submerge by pressing on its back. Again see that the prints do not stick to each other, and turn each print two or three times. They should be in the fixing bath not less than twelve or fifteen minutes, and a few minutes longer will do no harm. At the end of, say, fifteen minutes, pour away about one half of the fixing bath and slowly fill up with water. Turn the prints again, and then transfer them one by one to another roomy dish and wash in running water for a couple of hours, or in a dozen changes of water every five or ten minutes. Then hang up to dry, using either clips or pin a corner to the edge of a wooden shelf or long lath suspended in a cool, airy place.
Alum Bath.—Hot weather considerably increases the danger of the gelatine melting. To meet this trouble the following plan has to be resorted to:—
8. Dissolve common (potash) alum, one ounce in a pint of tepid water. Let it stand until cold and pour off gently the clear part should any sediment appear. After washing and before toning, place the prints in this alum bath for about ten minutes and again wash before toning for ten or fifteen minutes in running water.
The Combined (Toning and Fixing) Bath.—The general weight of opinion is not in favour of combining these two operations at one time when reliable results are desired. Nevertheless, there are times when this method may be found a convenience and yield results which are all that may be desired. The following bath is a favourite with some workers:—