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.
Toning In The Platinum Bath. Phosphoric acid sometimes results in rendering yellow, muddy prints, on account of not being absolutely pure, or because of its action when used with water containing certain chemicals. If this trouble should arise citric acid may be substituted and the platinum solution can be prepared as follows:
352. Dissolve 8 ozs. citric acid in 8 ozs. hot water. Label this "Citric Acid Solution."
Prepare the Platinum Stock Solution as follows:
Citric Acid Solution........................
Shake well until all the platinite is dissolved.
353. For use take,
Platinite Stock Solution..........................................
. 2 drs.
354. Pour the bath into your platinum tray, which must be used for this purpose only, and place the prints in the bath, a few at a time. Keep them in motion, toning until the highlights are perfectly clear and all trace of red has left the heavy shadows. Ordinarily, there is no danger of toning too far in the platinum bath, but there is no need of carrying prints beyond the point at which they appear clear, with the red entirely toned out. Sometimes carrying prints too far in this bath is likely to flatten the tone and injure brilliancy. This is the case, however, only where very strong platinum solution is used. When prints go into this bath first the whites become muddy, but in a short time they begin to clear. Keep prints in this bath until the whites are thoroughly cleared and every trace of brown or purple is removed, even from the deepest shadows. A slow platinum bath gives olive tones, a quick bath gives black tones. If the prints are toned rapidly in the gold bath, they must tone the same in the platinum bath, and vice versa.
Washing After Platinum Toning. As they are toned, place them in a tray of clear water until all are toned, and then they should be washed in two or more changes of clear water, in order to free them from the acid of the platinum bath. Unless this is done the acid will be carried into the hypo and cause bleaching of the prints. Prints coming from the platinum bath - this solution being strongly acid - are in an acid condition. For this reason, after all prints are toned in the platinum bath it is quite important that they be thoroughly washed to remove this remaining acid, because if this acid is carried into the hypo bath it will produce sulphurization and yellow whites. Wash through five changes of clear water, handling each print separately. If you find that the last wash water still tests acid it would be well to place the prints in an alkaline bath, prepared as follows:
356. To 100 ounces of water add 2 drams saturated solution carbonate of soda, or borax. Handle prints over in this bath thoroughly and then give them one more change of clear water, when they will be ready for the fixing bath.
357. When there are large batches of prints to tone, especially collodio carbon prints, there is danger of toning some of the prints a little more or a little less in the gold bath; and as the depth of tone in the gold bath governs the color of the tone in the platinum bath, there will be a difference in the shade of the finished print. Before fixing, in order that the prints may be of a uniform tone, place them in a sulphite of soda bath, as follows: