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.
Quality Of Tone. The final tone produced in the platinum toning bath is almost entirely governed by the depth of toning in the gold bath. If only the whites are clear in the gold bath, the resulting tones in the platinum bath will be strongly olive. If prints are toned to a chocolate brown, they will make beautiful olive tones. Prints toned to a purple with the deeper shadows a slight cherry color in the gold bath, will produce a good black and white tone in the platinum bath.
179. Remember, prints from a strong negative will stand vigorous toning; weak prints require gentle toning. Therefore, strong prints may be toned faster and in a stronger bath than prints from a weak negative.
180. If the prints are carried too far in the gold bath there is little or nothing left for the platinum bath to do, and the print instead of toning to a black olive or black and white tone, will turn brown, oftentimes producing a disagreeable, muddy effect.
Action Of Salt In Toning Bath. Salt is added to the gold bath for the purpose of acting on the free silver which is still in the print. This will precipitate the free silver of the print which is left from the washing. It is almost impossible to wash the prints with the same result every day, the age of the paper, temperature of the water, and quantity of prints changing every time a toning is made. This being the case, you will find more or less free silver when the prints go into the gold bath. The free silver takes up part of the gold deposited. If the prints are put in the hypo bath in this condition the tones will change, as you have only a surface tone and it oftentimes gives much warmer effects than you had produced with the gold bath. But with salt in the gold bath, the free silver is precipitated and when the gold deposits, it will be on a permanent base and give you a tone that will hold.
182. The true tone of the print is the tone as it appears when examined by transmitted light - looking through it - and the same tone should appear on the surface of the print. The salt in the gold bath will assist in producing this result. It will also give you rich strong shadows, save the detail and the half-tones, and also aid the action of the gold.
183. Salt, however, should be used with care and judgment, as too much is apt to flatten the tone of the prints, and too little will have practically no effect. If an extreme quantity of salt were used it would also preiv - 5 cipitate the gold and the prints would refuse to tone. Lack of salt in the gold bath will often cause uneven toning.
184. Gold is added to the bath for the purpose of toning the print, or changing it from red to any tone desired down to the blue, and the amount of gold in a bath regulates its speed, other conditions being correct. A formula may call for one dram or two or three grains, but the only true test of the amount to use is by testing for speed with a print when the bath is made.
185. A gold bath should have a speed of five to eight minutes. If not fast enough, add more gold to increase the speed. If the test print shows the bath toning too fast, add more water, which will reduce the speed. Should you find, during toning, that the bath is working too slowly, the number of prints already toned having used up the gold, more gold should be added. Always neutralize the gold before adding to the bath, by putting the gold into a graduate and adding an alkali until it turns red litmus paper blue. If you add acid gold to a bath without neutralizing it may throw it out of balance, sometimes causing the bath to bleach matte papers, producing pink whites in the platinum bath.