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.
519. Platinum paper is put up in tin tubes and sealed with rubber tape. The sealing is to prevent the air from coming in contact with the paper, and to keep it free from moisture. Each can is supplied with a small package of calcium chloride preservative. This preservative is used to absorb all moisture. If the can were left open for any length of time the air would affect the paper, and from paper affected thus it is almost impossible to produce good prints.
520. The effect of dampness is a lack of vigor, a general muddiness of tone, and where the paper has been exposed to its influence for some days it injures the beauties of the whites. The paper will keep for months, but must be stored in a cool, dry place, in the cans in which it is supplied.
521. In extremely warm summer months a good plan is to place the paper in a refrigerator, or some other cool place. The can containing the paper should always be perfectly sealed with a rubber tape.
Caring For And Preserving The Paper. The majority of failures in platinum printing and developing are caused by neglect in caring for and preserving the paper. The greatest trouble is caused by the paper becoming moist or damp. Where it is purchased in cut sheets there is not so much danger of moisture as when you buy it in rolls and cut it up to the required sizes.
523. For the convenience of consumers the manufacturers supply this paper in all regular sizes, a dozen sheets to a can, and it is advisable for those who do not use the paper in large quantities to buy the cut sheets, and only a dozen at a time. For those who are using large quantities of paper, of course, it should be purchased in rolls, as there is considerable saving in cutting the paper to all sizes.
524. Care, however, must be exercised in the handling of the paper. Never allow the fingers to come in contact with the surface of the paper. It is advisable to cut up only enough for the day's printing, then replace the roll of paper and preservative in the can, sealing it up carefully with the rubber tape. The cutting of the paper must be done in a subdued light, and the room must be perfectly dry.
525. The paper which you have cut for use should be placed in another can or light-tight box containing preservative. A wooden box lined with black paper and fitted with a light-tight hinged lid is preferable, and the box should be made large enough to hold both the printed and unprinted paper; a partition in the center will separate the one from the other. Always place the paper in the box sensitive side down. Keep the lid closed as much as possible. If the box is allowed to remain open, or the paper removed from the tube for a few hours before using, the effect of the dampness will be noticeable in the lack of strength and brilliancy in the print. Dampness will cause the highlights to print gray instead of pure white.