474 HANDBOOK OF PHOTOGRAPHY 



sensitive or not — with greasy fingers may cause blisters, though it is more apt to 

 result in white finger marks in the finished print. 



The sensitizer may be either slightly alkaline or slightly acid, but the best results 

 are secured when it is as nearly neutral as possible. 



More or less contrast may be secured by varying the strength of the sensitizer, a 

 strong solution producing a faster printing and softer working tissue, whereas a weaker 

 sensitizer gives a slower printing and stronger working tissue. The same result may 

 be secured by varying the time of immersion in the sensitizing bath, though the writer 

 pi'efers to accomplish this by varying the concentration of the bath rather than by 

 varying the time. The possible limits of concentration, beyond which it is not safe to 

 go, are ^ 9 per cent for a weak bath, and 6 per cent for a strong bath. 



A carbon print, when dry, may often be waxed and polished to advantage, as 

 described in the section on Platinum Printing (see page 478) and here the damage to 

 the surface texture is less than with platinum since the carbon print already has a 

 gelatin surface which masks the texture of the support. 



From the description given of the process, with the list of possible failures, it may 

 seem that carbon printing is a very complicated and difficult operation, but this is by 

 no means the case. If ordinary care is used, none of the possible failures is likely to 

 occur, and with a little practice the entire operation may be carried through rapidly 

 and successfully. As an illustration of this, the writer has known a man who did 

 carbon printing for a professional studio, many years ago, when carbon was in vogue 

 for portraits. This man, working alone for a 10-hr. day, was required, as his regular 

 day's work, to sensitize, print, transfer, and develop 200 carbon prints a day — which 

 would seem to be enough to satisfy almost any amateur. 



Carbro Printing. — The word "carbro" is a combination of the first syllables of 

 "carbon" and "bromide," and the process is so named because it is a method whereby 

 a true carbon print can be made from a bromide print, without the use of light. In 

 practice, the sensitized carbon tissue, instead of being dried and printed under a nega- 

 tive, is squeegeed into contact with a bromide print while still wet, the gelatin becom- 

 ing insoluble not through the action of light on the sensitizer but through the chemical 

 reaction between the sensitizer and the silver of the bromide print. Stripping and 

 development follow in much the same manner as with carbon, the final result being an 

 actual carbon print, exactly as in the previously described process. 



Advantages. — The advantages of carbro are the same as those of carbon, with the 

 additional ones that no very strong printing light is required, that enlargements can 

 be made without making an enlarged negative, and that multiple prints can be made 

 without the need for registration. 



Disadvantages. — The disadvantages and possible failures are those of carbon, 

 plus the fact that carbro is decidedly more temperamental than carbon, demanding a 

 closer adjustment of the controlling factors if success is to result. 



The Bromide Print. — There are two methods of working carbro, the transfer and 

 the nontransfer methods. In the former the sensitized carbon tissue is left in contact 

 with the bromide print long enough for insolubility to take place, being then stripped 

 off and squeegeed to a piece of transfer paper, where it is developed. In the non- 

 transfer method, the sensitized carbon tissue is developed directly on the bromide 

 print, which then acts as the final support for the picture. 



If the transfer method is employed, almost any bromide, chlorobromide, or 

 chloride paper can be used, but if the nontransfer method is preferred, care must 

 be taken that the original silver print is made on a paper having a soft gelatin. Most 

 of the American enlarging papers are hardened in manufacture, and some have a 

 protective supercoating of hardened gelatin; such papers cannot be used for non- 

 transfer cai'bro, since it is almost, if not quite, impossible to soften this hard gelatin 



