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.
Note. Carbon tissue sensitized with the spirit sensitizer prints much faster than when the bichromate sensitizing is used, the average Pyro developed negative (one that is not too dense) requiring about one and a half to two minutes to print in sunlight. In all cases of overprinting with this tissue, use hotter water for developing; in cases of under-printing the water must be kept quite cool.
Drying Tissue. Some manufacturers make what is called a daylight tissue, in which the paper support has a non-actinic quality. Such carbon tissue, after sensitizing, can be squeegeed to ferrotype plates, and then placed on edge to dry, instead of being hung up in a drying-room. Tissue treated in this way dries flat, so that contact with the negative is readily assured. At the same time, it is kept away from the light and from fumes, etc., during the drying process, which is always a delicate stage of the work; consequently, many of the best workers prefer this method of drying their tissue.
Reversing Negatives To Obtain Non-Reversed Prints, By The Single Transfer Process. As previously explained, the single transfer process yields reversed prints when made from an ordinary negative. If the print is made from a film negative, of course the print can be made through the back of the celluloid support, and then there will be no reversal of the image. Of course in portraiture, landscape or pictorial work, a reversal is of little importance, but still it is sometimes desirable to have the image the right side to. Where many prints have to be made off the one negative, some workers prefer to reverse the negative itself, rather than to go through the double transfer process with each print, as the double transfer process offers more chances for failure than the single transfer.
308. To reverse the film of a negative, it should first be hardened, for about five minutes, in a 10% solution of formalin, to which a few drops of glycerin have been added. The film can then be cut around through to the plate, about an eighth of an inch from the edge, and then placed in a bath made up of
Hydrofluoric Acid .........................................
300. Rock the tray gently and the film will begin to loosen from the glass at the edges. Avoid placing your fingers in the solution. Place a piece of moistened, fluffless blotting-paper over the film and gradually lift it away from the plate. The film is then washed carefully, and next placed into a tray of clean water, into which a clean glass plate has been placed. It is best to flow this plate with a substratum of insoluble gelatin. The water will soften the gelatin, and then, with the negative film in the water, but reversed, the plate and film are squeegeed together and removed from the water, care being taken that no air-bells remain under the film.