There are a very large variety of toning bath formula;, many of which are given under Toning Bath.
After washing, the prints are placed one by one into the toning solution, which should be contained in a white porcelain dish used only for that purpose. The depth of the solution should be at least half-an-inch Too many prints should not be toned at once, as the operator should have complete control over each one. They should be kept constantly moving, and prevented from adhering to each other.
The temperature of the toning solution should be between about 65 deg. and 75 deg. Fahr., except with gelatine prints, when, of course, it must be colder, or the gelatine would perhaps dis solve. In toning the following should be noted: Hard intense prints require vigorous toning, and should be placed face downwards in the solution. Weak prints require gentle toning. Toning the prints with the face downwards hastens the operation; with the face upwards it retards it.
The greatest enemy of the toner is hyposulphite of soda. Every precaution must, there fore, be taken that this substance does not reach the toning bath, the toning and fixing operations being kept as separate as possible.
When the desired tone (as viewed by transmitted light) is arrived at, which should take at least ten minutes, the prints are removed. Practice only will enable the operator to know with certainty when to remove the prints from the gold bath, as this differs with the different solutions. With some the prints change to a considerable extent in the fixing bath. With regard to the correct illumination for the toning operation, some prefer to work in dull, diffused daylight, and others by gas or other artificial light. With the latter, of course, allowance has to be made for the .
different appearance of the color when viewed by daylight.
Upon removal from the toning bath the prints are laid in a dish of cold water. To prevent further toning by the action of the solution in the print, a little common salt should be added.
The failures most likely to be met with in the toning process are the following: If the prints tone too rapidly the bath is too strong in gold. Unevenness of tone will also arise from this defect. The prints will also lose a great deal of their tone in the fixing bath. Uneven toning is also the result of the bath being acid or too warm. If the prints are allowed to stick together or to the sides of the dish, patchy unevenness will also be caused, or if fresh gold solution be added while the prints are in the bath. If the prints tone too slowly it is possible that the solu tion is too weak in gold. Sometimes they will refuse to tone from this cause, or from the bath being contaminated with foreign impurities, or from its being too cold.
Loss of tone in fixing is an annoying defect, more often occurrent with some gold than with others, also with inferior samples of gold. This can sometimes be avoided by making the fixing bath acid with acetic acid, and then neutralizing with ammonia till distinctly alkaline to test paper. If not made alkaline, however, a yellowness of the whites will be caused. This latter defect may be caused by over-toning. See also Platinum toning, Palladium toning. Osmium toning, and Iridium toning.