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.
266. No bath will tone prints from strong, contrasty negatives and prints from weak, thin negatives, in the same batch, and give uniform results, unless the quantity of alkali added to the bath is regulated according to the character of the negative from which the prints are made.
267. A good printer, toning a large batch of prints from different kinds of negatives, will sort over his prints in the last wash water, laying the contrasty ones on one side of the tray, the weak, soft ones at the other. First he will use one of the softer prints to test his bath, adding enough alkali to hold the highlights and half-tones from bleaching. He will then tone all the prints from the thin negatives and test the bath again before toning the contrasty prints, using as a test, a print from a hard negative. It will be found necessary to use more alkali to hold the highlights in the contrasty prints. After adding enough alkali to prevent the highlights in the contrasty print from bleaching, tone the rest of the batch. This is the only way to average up tones in a large batch.
268. On the other hand, if the prints in a large batch are not sorted out and a contrasty one is used to test the bath, the prints from the soft negatives will not clear up, and will result in muddy highlights and half-tones. Or, if a soft print is used to test the bath, the contrasty prints will bleach in the highlights. That it will always pay to sort out the prints in the last wash before toning, and add alkali to the bath to suit the character of the prints, is apparent.
269. A strong, contrasty print will stand more toning than a print from a thin negative. The latter will " blue up " and flatten in the hypo, if toned as far as a print from a contrasty negative. Another point a printer should remember is, that old paper does not require as much alkali as fresh paper.
Flat Prints. Caused by printing from a flat, weak negative. They are oftentimes the result of insufficient toning in the gold bath, which leaves the shadows a bricky red. An excessive amount of salt in the toning bath will also cause flatness.
Prints Toning Too Slow In Platinum Bath. There are a number of reasons to which this may be attributed.
272. Using the same tray for both gold and platinum bath. To all gold toning trays a certain amount of gold will adhere. This gold precipitates the platinum and, therefore, the benefit of the platinum is not obtained.
273. Using an iron tray, commonly known as japan, or enamel. If these trays are chipped in numerous places, as they often are - exposing the iron - you will find that the acid in the platinum solution will cut into the iron. This will cause a precipitation of both iron and platinum.
274. If the platinum bath is neutral, or slightly alkaline, the platinum will precipitate. This might occur if the water used in preparing the platinum bath was strongly alkaline. If so, it will be necessary to acidify the water with phosphoric acid before adding the platinum solution.