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.
Judging Proper Depth Of Printing. A very good way to judge when your platinum print is printed to the proper depth is to be guided by the strongest highlights. If in a portrait, they are generally found upon the forehead or nose; in landscapes, usually in the sky. These being the highest lights they must not be tinged a particle. Print up to that stage, and no more, and use these highlight portions for your guide in printing. After a few trials you will be able to judge exactly.
535. The exact depth to print can only be determined by experience, for different classes of negatives will require different depths of printing. Strong negatives should be printed in strong light, and when printing in the open sunlight use one thickness of tissue paper or a ground-glass over the negative. Weak negatives should always be printed in subdued light.
536. Caution - Avoid over-printing; always endeavor to print to the exact depth that will give a nice, bright print with about one-half minute development. A print which is slightly under-exposed will be improved by long development. One which is over-exposed, however, cannot be improved in the development.
Doctoring Negatives In The Printing. There are few negatives made that cannot be improved somewhat by a little dodging in the printing. Platinum paper lends itself very naturally to dodging. For notes on dodging in the printing see "Special Pointers for the Printer."
Examining Prints During Printing. Prints should be examined in subdued or artificial light. Care must be exercised that the prints are not turned back too far during examination, as this would not only make fogging more likely, but would also be apt to break the paper. Do not examine the prints too often. After a little practice you will be able to judge from the strength of the negative how long it will require to print to the proper depth, and frequent examinations will then be unnecessary.
The Developer. We recommend the prepared developer put up by the manufacturers, as the proportions are exactly right. The full amount of each package of crystals should be dissolved at one time, as the different crystals are not equally mixed in the package, and should you attempt to divide it into two or more parts you would be quite apt to have more of one chemical in a certain division than in another. These developers may be procured in large or small packages, so there is no necessity for using less than a full package, as the developer keeps well when in solution. In fact it improves with age. Therefore, there is no saving in preparing small quantities.
540. The crystals must be dissolved in hot water and allowed to cool. Never prepare this bath in an iron or tin dish. Use either porcelain or agate ware. The tin or iron would affect the developer and spoil it. After the developer is all dissolved and cooled, pour it into a large bottle. Cover or cork the bottle to keep it free from dust. Label this bottle "Platinum Developer Stock Solution."
541. For those who desire to prepare their own developers we supply the following formula:
Neutral Oxalate of Potash................................
542. Stir until thoroughly dissolved, and when cool place in a large mouthed bottle. Platinum developers may be used over and over again. A good plan is to make up about 100 ounces of the solution and use only part of it for developing. When through developing, pour the used solution into a separate bottle labeled "Used Developer," keeping up the required amount of developer by replenishing from the fresh stock solution.