SPECIAL PRINTING PROCESSES 467 



about the same quality is desirable as in the case of platinum printing. It is. of 

 course, not necessarj' to exhaust the scale of the paper; medium or low-keyed prints 

 may be made as well as with any other medium, though when a very high key is 

 required, carbon is not so satisfactory as platinum. 



Since the print is not developed on the original backing paper but must be trans- 

 ferred to some other support for development, it follows that, if the picture is to be the 

 right way around, it must be printed from the back of the negative, or a reversed 

 negative must be made. In pictorial work it is usually satisfactory to print from the 

 back of the negative, for, whether the negative is on film or on glass, there will be 

 little or no perceptible diffusion if a concentrated source of light is used and the printing 

 frame is not moved during exposure. If, however, the negative is to be on a glass 

 plate, a diffused source of light is used, the picture must be the right way around, and 

 the utmost in fine detail is required — all of which is a rather unusual combination of 

 circumstances — then a reversed negative must be made, or double transfer must be 

 resorted to. 



The Tissue. — "Tissue" is rather a misnomer, since the combination of backing 

 paper and gelatin emulsion is rather heavj-. The tissue is sold insensitive, in cut 

 sheets 8 by 10 in. or in rolls 30 in. by 12 ft. It should be stored in a cool dry place, in 

 which case it will keep indefinitely before sensitizing; if it is allowed to remain moist 

 for any length of time, bacteria maj^ grow in the gelatin, and the prints, on develop- 

 ment, will show irregular blank patches. 



A roll of thoroughly dry tissue is very intractable and very brittle; it is almost 

 impossible to unroll and cut it without cracking the gelatin. It may be rendered 

 more flexible bj^ allowing it to stand for a few hours in a damp atmosphere or, in 

 emergency, by steaming it slightly over a teakettle, when it can be easily handled and 

 cut. The roll should then be permitted to dry out again, and the cut pieces should be 

 stored under moderate pressure and allowed to become thoroughly dry before 

 sensitizing. 



The various colors of tissue differ to a considerable extent in their working charac- 

 teristics, as regards not only printing speed but also scale of gradation. One of the 

 pleasantest for general use is the Ivory Black, which is a pure translucent black of very 

 long scale; being translucent, it takes a tone from the transfer paper, so that a print 

 in this tissue on a white paper is a pure black, whereas on a toned paper it will have a 

 very pleasing warmth of color even in the deep shadows. Since the gelatin of this 

 particular tissue is heavily loaded with pigment, it is possible to make prints in a high, 

 or even a medium, kej^ which are free from luster even in the shadows. 



Transfer Paper. — When the carbon tissue is printed, it is the layer of gelatin which 

 is next the negative that is first insolubilized. Therefore, if it were developed directly 

 on the backing paper, only those portions which had been printed clear through the 

 gelatin would adhere to the support, the other areas washing off, and we should have 

 merelj' a silhouette of the deep shadows. For this reason, it is necessary to transfer 

 the layer of gelatin to another support., strip off the backing paper, and develop the 

 gradations from the back of the layer of gelatin. 



About 15 different transfer papers of various textures and colors are commercially 

 available, or a transfer paper may easilj^ be made by fixing out a sheet of bromide or 

 chloride paper without exposure to light, using plain (not acid) hypo, and washing as 

 usual. If this is done, care must be taken to choose a bromide paper which is suitable 

 for bromoil work, many of the commercial silver papers having a protective super- 

 coating of hard gelatin to which the carbon tissue will not adhere. 



In general, the writer prefers to make his own transfer paper, which is readily done, 

 as follows: 



