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.
How To Tone. First, proceed to test your gold bath by trying one print. Place the print in the bath and with the right hand spray the solution over the print, watching it tone. If the highlights and shadows tone equally you will know that the bath is working properly. Should they tone chalky, bleach, or eat away, the shadows refusing to tone, you will then recognize that the bath is still too acid, or at least it is not sufficiently alkaline. Add a few drops of borax and continue to add cautiously until the bleaching ceases. After adding alkali until the red litmus paper has turned blue, indicating that the bath is alkaline, if the prints still show signs of bleaching, place a fresh print in the bath. If the bleaching shows in the second print a few more drops of borax should be added. Continue adding very cautiously until bleaching ceases and the print tones down to a rich purple in about 6 to 8 minutes. Should the test print, after toning this far, look clear and snappy in the whites, not bleached nor muddy, the bath is at the right stage and you can proceed with the remaining prints. Judge tone by looking through the prints, or, in other words, examine by transmitted light.
350. It is not advisable to judge prints by looking upon the surface while they lay in the tray. Always hold them before the light, looking through them, and when clear and even throughout you will know that they have been sufficiently toned. For black and white tones the print should be carried to a rich purple, leaving considerable warmth in the shadows. As the prints are toned, place them in a tray of clear water until you have completed the entire batch. When all are toned, wash the prints through at least five changes of water, handling them over singly in the same manner as in the first washings, thus avoiding blisters which sometimes appear if old paper is used, or when wash waters are not of uniform temperature. To the second wash water, after gold toning, add 1 02. of salt to every gallon of water used; handle over carefully, separating the prints in the salt bath for five minutes; then wash well in three changes of fresh water. The object of this thorough washing after toning is to free the print from the excess alkali which has been taken on in the gold bath. Should this alkali be carried into the platinum bath, which is an acid solution, it would cause the platinum bath to become alkaline and throw down the platinum to the bottom of the tray instead of depositing it on the prints; thus making it necessary to add more platinum stock solution to the bath in order to secure any tone at all. This, however, is an unnecessary waste of platinum, as well as time, which can be avoided by properly washing the prints to free them from alkali, and have the platinum bath in an acid condition. After freeing the alkali from the prints by thorough washing, they are ready for the platinum bath, which should be prepared at least an hour before using.