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.
Preparing Sensitizing Bath. The sensitizing bath should be prepared exactly according to the directions given in the lesson. If the bichromate does not dissolve readily the water is too cold. Warm water (temperature not less than 110° Fahr.) should be used to dissolve the bichromate, and it must be thoroughly dissolved before being used. The bath, of course, must be cooled to the proper sensitizing temperature before placing any tissue in it, and should be filtered through cotton each time before using.
Tissue Cracks When Unrolled. If the tissue is very hard and crisp- i. e., exceptionally dried out-care must be exercised not to crack the surface of the pigment when straightening it out. It should be laid on a frame over a tray of water and covered with a blotter, and allowed to remain in this position for two or three hours, until it has taken up enough of the moisture to become slightly flexible. In this condition it will easily unroll or flatten out when placed in the sensitizing solution.
Sensitizing The Tissue. Little or no difficulty should be experienced in sensitizing the carbon tissue. One edge should be inserted in the bath and the tissue gradually unrolled, at the same time thoroughly applying the solution to all parts with a camel's-hair brush. At the end of one minute the tissue will be thoroughly limp and should then be turned over. Brush the back of the paper for another minute, so as to have the solution penetrate this side evenly, and that all air-bells be removed. The tissue should now be turned over and the pigment side brushed carefully for the remainder of the time required to sensitize.
Tissue Dissolves During Sensitizing. Should the tissue dissolve while sensitizing, and especially when touched with the fingers, the bichromate bath is too warm. It should not be warmer than 70° at most; a much lower temperature is advisable. In summer the sensitizing solution should be placed in an ice water bath; i. e., the tray containing the sensitizing solution should be floated in a larger tray, which latter should contain water with a piece of ice in it. If this is not convenient the regular sensitizing tray should be cooled by allowing the water from the faucet to run into it for some little time, and if ice is available a small piece should be allowed to stand in the tray for a few minutes before pouring in the sensitizing solution. The bottle containing the sensitizing solution may be easily cooled by placing it under the tap for some time, or setting it in a pail of ice water.
Drying Tissue. If the tissue refuses to dry within the required length of time, the room in which you are attempting to dry it is too damp or too cold. The room should be perfectly dry and the temperature at such a degree that the tissue will dry in five or six hours. A specially arranged drying-box, which may be artificially heated, and a fan applied at one end so as to cause a thorough circulation of the air, will be a decided advantage over attempting to dry in a room, yet if but little carbon work is to be done good results will be secured if the room is at the proper temperature and perfectly dry.