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.
Loading The Printing Frame. As platinum paper is very sensitive to strong light, loading the frame should be done in diffused light. Direct light falling on this paper will ruin it and cause it to fog. For the benefit of those who have never used this paper, we would say that the sensitive side is the side which appears quite yellow. Place your negative in the frame, after carefully dusting it, and then place the paper on the negative, with the yellow side next to the film.
527. While it is not absolutely necessary, yet it is advisable to back up the paper on the printing frame with a piece of heavy cloth, paper or thin rubber pad. The negative and pad must be entirely free from moisture. The pad will answer two purposes; first, absorbing any moisture or dampness, and second, to bring the paper in perfect contact with the negative.
528. Exercise care in placing the paper upon the negative, that you do not touch the sensitive surface with the fingers. This is important, more especially when the hands perspire freely, as the acid moisture from the fingers will stain the paper, and when developed will show black stains.
Quality Of Negative Required. Any negative that will make good prints on any printing-out paper will give good platinum prints. Printing from a very thin, weak negative will always result in flat prints. A medium fast printing negative, with plenty of detail in the shadows and plenty of strength, still retaining the detail in the highlights, will always give good prints. Under-exposed and under-developed plates are practically worthless for platinum printing.
The Grade Of Paper To Use. Rough paper should be used when sketchy effects are desired, and the negative should have good strong printing quality. In portraiture this grade should be used on large heads, but never on small ones. The smoother grade paper should be used where fine detail is desired and for small pictures.
Printing. Correct exposure is ascertained by inspection of the paper in a rather weak white light in the usual manner. The sensitized surface before exposure to light, as before stated, is of a lemon color. During exposure the parts affected by light becomes a grayish brown color, and sometimes an orange tint under those parts of the negative which present clear glass or nearly so. As a general rule, all parts of the picture except the highlights should be visible when the exposure is complete. Damp paper gives a less visible image than dry paper; hence it may easily be over-exposed.
532. When printing from thin negatives, care must be taken not to over-expose. As soon as the image is faintly visible it may be considered enough. Negatives that have been well timed and developed to fair density will be found the best. A thin, weak negative will give gray prints; on the other hand, negatives under-timed and underdeveloped will produce black and white prints without detail in the middle or higher lights. Such negatives should be masked. (See "Doctoring Negatives.")
533. The secret of platinum printing is judging the proper depth to print. It is advisable for a first experiment to use only small pieces of paper for printing until you have learned to judge the proper printing depth, then the regular size can be applied. It is also advisable to select a normal negative to print from with your first experiments. After loading the frame, place in sunlight and print until the image is visible in all parts, although only faint outlines are visible in the stronger portions of the negative. The print before developing will look light and have a weak faded appearance.