SPECIAL PRINTING PROCESSES 491 



proper conditions of heat and humidity, drying will not take more than a few minutes, 

 but it may be hastened bj^ an electric fan or over a gas stove, taking care to avoid 

 scorching. 



The paper should be printed as soon as it is dry, since it keeps in good condition 

 for not more than a few hours at most. 



Printing.- — ^It is, of course, impossible to say definitely how long a time the printing 

 will take, but as compared to other quality mediums, gum is fairly rapid. As an exam- 

 ple, the average printing time for one of the writer's negatives, printing in unobstructed 

 July sunlight for the high lights, will be from 2 to 3 min., and for the half tones and 

 shadows it will range from 2 min. to 20 sec. 



Development. — Development should take place as soon as printing is completed, on 

 account of the continuing action which occurs in gum as in other colloid-bichromate 

 mediums and which cannot here be arrested by washing the print in cold water, as with 

 carbon and Fresson, as the gum is soluble in water at any temperature. 



To develop, the print is washed in several changes of cool water, to remove most of 

 the sensitizer, and is then turned face down and allowed to float on j4 to 1 in. of water 

 in the tray. It may be lifted and drained from time to time, to follow the progress of 

 development. The stage of development is noted by watching the water that drains 

 from one corner back into the tray; this water will be seen to carry with it more or less 

 pigment, the amount of color gradually diminishing as development proceeds. If 

 the printing has been correctly timed, H' hr. will find the print developed to the proper 

 point, which will be indicated partly by the general appearance and partly by the fact 

 that the drainings will be practically free from pigment. It is not necessary that 

 they carry absolutely no pigment whatever, but only a trifling amount should be seen 

 running off the print. Here again, experience is the only precise guide. Obviously, if 

 the print is too light at the end of ^i hr., it is underprinted, and if it is still too dark, 

 printing has been excessive. In neither case is it necessary to throw the print away; an 

 undertimed print should be developed as far as it will go and made the basis for a 

 multiple print, and one which is overtimed can be forced bj^ the use of warm water — up 

 to 212°F. — or by the use of a small amount of alkali in the developing water, 

 as described in the section on Carbon Printing. In the case of gum, however, the 

 addition of alkali has little effect at normal temperatures; it is most effective when the 

 water is warm. In any case it should be used very cautiously, as an excess causes 

 the same trouble as in carbon, viz., a complete washing out of the lighter gradations, 

 and perhaps flaking of the film. 



The colloid film of a gum print is much softer and less likely to tear than that of 

 either a carbon or a Fresson print, consequently much more local development may be 

 indulged in than with either of the other processes. In fact, the possible modifications 

 are so great that there is a serious temptation to overdo them, producing a result which, 

 even though it may not be obviously scratched up in imitation of a charcoal or pencil 

 drawing — as far too manj^ gum prints are^ — still is evidently false in its values. This is 

 a danger which should be guarded against. As in any medium, only such local modi- 

 fications as are definitelj^ necessary should be made; the temptation to play with the 

 print should be sternly resisted. 



Since the purpose in local modification is to remove the softened gum from the 

 paper, many ways of doing this will suggest themselves. Water from a hose may be 

 allowed to run on the spot which is to be lightened; if the hose is held at such a height 

 that the water falls in drops, the effect will be greater than that of a continuous stream. 

 A spray from an atomizer may be used, or a jet from a washing bottle, or, if this is not 

 sufficient, a soft carael's-hair brush. It is not generally advisable to use a stiff brush, 

 since this tends to leave a scratchy appearance. Whatever method of local modifica- 

 tion is used, the effect will be less obvious — and less likelj^ to be unpleasant — if the 

 work is done under water. 



