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.
Clearing Bath. As soon as a print is fully developed it must be placed, face down, directly into a clearing bath made up as follows:
552. Formula for Clearing Bath.
Hydrochloric Acid (Muriatic Acid) C. P.....................
... 1 ozs...
553. Half fill the tray which you are to use for this purpose with this clearing bath. The quality of the acid used is very important - it must be chemically pure. Ordinary commercial acid will cause yellow prints. The prints must have 3 or 4 changes of acid clearing bath. Allow them to remain in each bath from 7 to 10 minutes and keep them separated. In separating the prints do not draw them over each other, but lift them up carefully. You will note that this paper when wet becomes very soft and pulpy, and the surface is, therefore, easily rubbed. Prints should never be put into clear water until they have passed through all the acid baths.
554. The extra heavy papers require at least five acid baths to properly clear them. They also require a little more washing on account of the weight of the paper. Never use water in the developer or clearing bath that contains iron, as iron has a tendency to turn the paper yellow. Soft water is best for this purpose.
555. It is important that the prints receive proper care in these clearing baths. Prints are not sufficiently fixed, or cleared, until the water of the last bath is as clear as pure water, showing no yellow tint. This is quite important, as permanent results can only be obtained in this way. The acid clearing bath removes all unacted-upon chemicals from the paper. A platinum print which has been properly treated is composed of nothing but metallic platinum and paper.
Final Washing. Wash in plain clear water, using plenty of water, carefully picking the prints over and over and wash them face up. Great care must be exercised that the prints are not rubbed, or the surface touched by prints rubbing togther. The texture of this paper is somewhat rough, and if you slide the prints over each other the back of the upper print is liable to rub the face of the under print. Wash from one-half to one hour. They are then ready to mount or dry. If prints are not to be mounted they can be flattened and dried in the following manner:
Flattening And Drying Unmounted Platinum Prints. First place the prints one by one on a large mounting glass, face side down. After all are on the glass, with the flat of the hand press the water from the prints; then lay a blotter over them and with a print roller expel all the excess water. Do not roll too hard. After surplus water has been mopped from the prints, pick them up one at a time and place a layer of prints face side down on a clear white, chemically pure photographic blotter. Place another blotter over these prints, then pass your hand or roller lightly over this blotter to absorb the excess moisture in the prints; remove this top blotter and cover prints with a white cardboard. The next layer of prints must be placed face up on the cardboard. Blot off the surplus water, remove the blotter and place on this print a fresh dry blotter. Follow this order with the remaining prints.
" Lockwood," or any spring clip that will grasp the edges of the print. If hung up at the end of the day they will be dry next morning. We recommend string in preference to wire, for the following reason: The wire in time will be affected by the different temperatures and becomes covered with rust, and when hanging up the prints the rust is apt to shake from the wire and settle on them, causing black spots.
559. Retaining Brilliancy. Note. - Platinum prints should not be allowed to remain in the various baths longer than is necessary, as they are likely to lose brilliancy from long soaking and the paper will also become soft, pulpy and hard to handle. When development is begun it should be completed without interruption, and as speedily as possible.
560. A good plan for the beginner is to develop the prints immediately after printing. If prints, however, are not to be developed at once after printing, place them in a tin tube, with a package of preservative, and seal the tube carefully. If the preservative were to come in contact with the surface of the paper it would cause white spots and streaks. This preservative is placed by the manufacturer in a small package which should never be broken.
562. (a) Paper must be kept dry at all times.
564. (c) The temperature of the developer has much to do with the final results.
565. (d) In developing, slide the print face up under the developer, so as to prevent the formation of air-bells. If any air-bells should form, break them at once by touching with the tips of the fingers.
566. (e) Prints must be placed directly from the developer into the acid clearing bath, without previous rinsing.
567. (f) Remember that the last clearing bath must be free from all yellowness. If this is so you can feel sure that your prints are cleared thoroughly.
568. (g) Remember that chemically pure hydrochloric acid (muriatic acid) must be used in the clearing bath. Never use commercial acid.