BROMIDE PROCESS The essential feature of the bromide process is its suitability for obtaining either contact prints or direct enlargements by artificial light, and the consequent facilities that it gives for secur ing any desired result with absolute certainty. If a print is produced which is not exactly in accordance with the result desired, a second exposure may be made while all the conditions remain absolutely constant, and the time of exposure may be so modified that the second print will give exactly the effect desired. In adopting the bromide process, the following conditions are desirable. A light that can be kept as uniform as possible, a means of fixing the relative positions of light and printing frame so that the distance between them is always the same, and the exclusive use of one brand of bro mide paper. The distance between the light and frame should be so adjusted that exposures will vary from ten seconds for a moderately thin negative up to forty or fifty for a strong or dense plate. It is impossible to work accurately if exposures are as short as two or three seconds ; such exposures cannot be timed with certainty, whereas longer exposures can be timed with an inappreciable percentage of error. Correctness of exposure is absolutely essential in bromide printing if good results are desired ; there is no more fruitful source of imperfect prints than incorrect exposure, and the consequent attempts to compensate by incomplete or forced develop ment. A perfect bromide print is one that has been so exposed that full development with a normal solution will give the contrast and depth required. In order to expose a print in this manner, it will be found desirable to make a preliminary trial exposure on a small slip of paper, selecting a portion of the plate that has part of the densest tones. An ordinary piece of paper may be cut into six or eight trial slips, and several may be exposed on different negatives and developed together. The development of these trial slips should be full, in order that the correctness of the exposure may be judged from the final appearance when in the fixing bath.
Another prolific source of loss of quality in bromide work is the system of using one portion of developer for several prints in succession. The prints last developed are inferior in colour and general quality, and if toning is afterwards performed, the colour is very poor and weak. For prints of moderate size, sufficient developer should be taken for one print, the solution used once and then thrown away. For small prints this is also the preferable plan, but as the quan tity of solution necessary is much larger relative to the size of the print, it may be permissible to use the same solution for two prints in suc cession, or, better, to develop two prints together. But this should be the limit.
Where practicable, as in the case of an incan descent electric light or an inverted incandescent gas burner, the frame should be placed hori zontally below the light for making the exposure. It will facilitate shielding parts of the negative during the exposure, and also the making of the exposure by uncovering and recovering the frame, using a sheet of card.
Diamidophenol and amidol are good developers for bromide prints, but they cannot be kept in solution satisfactorily for more than three days. The seriousness of this objection is realised when only two or three small prints are required, and then no more wanted for perhaps a week. Amidol is, however, a favourite with many workers, on account of the fine blue-black colour of the prints produced with it. Ortol is also a good developer for bromide paper, and it keeps for a long time in solution. Metol and hydro quinone form a developer that is a favourite with many workers, as it keeps well in solution. Excellent formula are as follow :— Diamidophenol Developer for Bromide Paper Diamidophenol (or amidol) 16 grs. g. Sodium sulphite . . 160 " 44 ,P Potassium. bromide , 4 „ 1 „ Water . . . . 8 oz. 1,000 ccs.