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.
Depth Of Printing. The printing quality of a negative has the same influence on matte papers as it has on glossy, i. e., it is not necessary to print as deeply from strong, slow printing negatives as from thinner ones. The slower the reduction of silver the stronger and more solid will be the resulting print. When printing from a dense negative, the highlights are, of course, restrained from printing until the shadows have been exposed for a considerable length of time to the strong light. When the highlights are properly printed the shadows will be very dark and deeply printed and will not lose any of the strength in washing. A hard, contrasty, slow printing negative, therefore, should not be printed as deeply as a flat negative.
161. Owing to the extra toning bath, which serves as a bleaching process as well as for toning, the printing of matte papers must be four or five shades deeper than for glossy. A good rule to follow is to carry the printing until the highlights are slightly tinted and continue so long as the print grows stronger - more solid and brilliant. As soon as it begins to fog over, and becomes muddy looking - causing it to appear weaker - it is fully printed and can be removed from the negative. The highlights must always be tinted, but pay no attention to the shadows, even should they bronze considerably.
162. If in doubt, a good method to determine how deep to print is to select a good well-timed negative and print it to the depth you judge is just right (from the above advice). Then make another print from the same negative, two shades darker. Wash and tone them together, and they will be excellent keys for judging future work. The right depth to which matte papers should be printed is probably the most important part of their handling. Although all the baths may be just right, if the printing is not deep enough the result will be a total failure. Beginners invariably under-print. Remember this and print deeply.
Judging Print By Transmitted Light. There is another way to judge prints in printing and toning, but it is unsafe unless cautiously done. When examining prints, if they appear very nearly printed, step back from the window into the subdued light of the room and look through the print, with the face side toward you. This will show the print much lighter than by looking on the surface. When judging prints in this way be sure and do so in subdued light, for the prints will be flashed if examined in strong light.
164. When looking through the print, observe the highest lights (the whitest parts of the picture) and if they appear just the least bit stronger than desired in the finished print, they have been carried deep enough. You will find these prints, when viewed on the surface, look as though they were over printed, but they will, when washed and toned, make the most solid prints.