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.
403. To Soften Contrast and Retain Delicate Detail add fifteen to twenty minims of 5 per cent. solution of ordinary alum to each ounce of concentrated solution contained in the sensitive bath.
404. In the Non-Transfer Method, the bleached image underlying the picture in carbon may be re-developed partially or entirely, and this may be made use of in various ways. For instance, a weak print may be converted into a strong print by re-development.
405. If a weak developer be applied with a brush, local intensification may be affected. A weak sky may be made heavier or other portions increased in strength, while the remainder of the bromide image may be eliminated by a 10 per cent. hypo bath. The underlying image may also be toned by the various methods advised for bromide or developing papers. After such re-development, or toning, the solution must be removed from the print by fifteen minutes' washing in running water.