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.
298. In the previous chapters we have given methods and formulae which, with practice and attention, will secure perfect results in carbon printing. There are various alternative methods which can be employed, provided the fundamental principles are understood, and many workers have favorite formulas for sensitizing the tissue or for clearing it.
299. The most recent method of sensitizing paper tissue is by the use of what is called spirit sensitizer, which is supplied in liquid form, ready for use, and can be applied just before you are ready for printing.
300. The object of this spirit sensitizer is to get over the great delay caused by the prolonged drying under the usual methods of sensitizing in the ordinary bichromate bath. Using the spirit sensitizer, the worker can sensitize his tissue only a short time previous to his putting the tissue out to print. It is easy to see, therefore, that the use of such a sensitizer has very many advantages. It can be used on any carbon tissue, but is intended particularly for the Autotype tissue, and can be purchased from any dealer in photo supplies.
Materials. The materials required for this method of sensitizing are few, only the sensitizer and sensitizing brush being required, outside of the materials listed in a previous chapter. The brush that comes with the spirit sensitizer can be used, or the worker can prepare one for himself, by wrapping a flannel cloth around a glass rod, the flannel being attached to the rod with rubber bands. Or, a stiff sheet of celluloid can be laid on a piece of flannel, the flannel brought over the ends of the celluloid, and then the two ends of the celluloid folded together and held in a clip.
Sensitizing. To sensitize the tissue take a couple heavy card mounts-or the cover of a plate-box will do-and pin the carbon tissue to it, face side up. This can be done in strong light. The sensitizing, however, must be done in a darkened room; one where velox can be handled safely will answer the purpose admirably. Take the bottle of spirit sensitizer and pour a little of the solution into a clean glass tumbler. Loosen the flannel on the glass rod or handle of the brush which accompanies the bottle, so that it overlaps the glass rod about half an inch. Dip it into the sensitizer, drain for a moment against the side of the glass, and then brush the carbon tissue with even strokes from side to side, allowing each stroke to overlap the previous one. This one coating will be found sufficient for most all work. However, if an extra strong print is desired the tissue may be brushed again in the opposite direction, care being taken that the brush is sufficiently wet; otherwise it will stick and cause streaks in the finished print.
303. The board with the carbon tissue pinned on it can be set in some dark corner to dry, and two or more sheets prepared while the first is drying, which does not take more than five or six minutes. After a few sheets have been sensitized the first ones will be dry and ready for printing. This is one of the greatest advantages of spirit sensitizer, for by the ordinary sensitizing with bichromate it is necessary to let the tissue dry for from five to eight hours.
304. After the tissue has been dried, the printing and transferring proceeds as in the instruction already given, with the exception that the temperature of the water when first starting to develop may be lower than when the regular bichromate bath is used.