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Bromide

developer, paper, negative, solution, acid, ounces and development

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BROMIDE PAPER.—A paper coated with a gelatino-bromide of silver (described under Emulsion, q.v.) and used for enlargements or printing by contact. This paper, of which there are several kinds, may be obtained having a smooth or a rough surface, the latter being most suitable for enlargements. It should be mentioned that there are two distinct kinds of bromide papers—negative bromide paper, a paper coated with the same kind of emulsion as used for plates, and employed in the camera for negative making, and a positive emulsion paper coated with an emulsion a little less sensitive to light. The following is a descriptive method of using the positive paper.

The exposure varies, of course, with the density of the negative and the quality and intensity of the light which varies inversely as the square of the distance from the radiant to the recipient. For a properly developed and correctly exposed glass negative, one second by diffused daylight, or ten seconds at a distance of one foot from an ordinary gas burner should suffice. An oiled paper negative requires about double this exposure, and an unoiled paper negative about five times the amount. Over- or under-exposure may be judged of upon development. An over-exposed print will present a poor and flat appearance, devoid of vigor in the shadows, and having an excess of half-tone, while a want of half-tone and a dark, heavy appearance of the shadows is due to under-exposure. As soon as the correct exposure is ascertained, any number of prints may be made without fear, for if the paper, negative, light, distance and exposure be the same in each case, the results must likewise be similar, and a large batch may be developed at one and the same time.

Developing is the next operation. The ferrous-oxalate developer gives the best results.

Puff, farmii1n will bc. cr; wan Solution No. 2 should be tested with blue litmus paper, which it should redden distinctly. If this effect does not take place, a very slight addition of sulphuric acid will probably suffice. These three solutions should be kept separately, and only mixed when required for immediate use, when they should be taken in the following proportions :—No. i, six ounces ; No. 2, one ounce ; and No. 3, one drachm, mixed in the order given.

Many modifications of this developer have been recommended, and consist chiefly in the addition of citric acid (about i drachm) to the oxalate solution (No. i), and the substitution of

the same quantity of the same acid in place of the sulphuric acid in the iron solution (No. 2) Another developer to be recommended is the hydrokinone developer. In twelve ounces of hot water dissolve Sodium sulphate 1 ounce Hydrokinone 15 grains Sodium carbonate r5 ounces Potassium carbonate t% ounces Potassium bromide 20 grains For sepia or brownish tones use an alkaline pyro developer, arranged as follows : Water t ounce Pyrogallic acid. to 2 grains Ammonia 2 minims Potassium bromide 3 grains Citric acid (sat. sol.) to drops After exposing the paper it is placed in a bath of cold water until limp. It is then removed and placed face upward in a tray, and the developer poured rapidly over it. The image should appear slowly, and should be strong, clear and brilliant, exhibiting, if correctly exposed, all the detail in about three minutes. The dish should be kept rocking : many ingenious contrivances having been made to do this automatically, although the hand supersedes them all. All air-bells should be removed from the film before the development has proceeded far, and when the shadows are sufficiently black the developer is poured off and the clearing solution added. In developing it should be remembered that a too rapid development gives a weak, flat image. A too slow development gives violent contrasts and great hardness. The addition of a further quantity of No. 2 solution strengthens the developer, while No. 3 tends to retard its action. By modifying the proportions in mixing the developer much softness and brilliancy can be obtained. For developing a print from a weak, soft negative mix one part of iron to six of oxalate. No larger quantity of iron than this must be taken, as it will then form a precipitate, and the devel oper will be spoiled. A short exposure and a prolonged development with the above developer will give brilliant results with a thin negative. With a dense, hard negative, however, with hard contrasts, a very small portion of iron solution should be added, say i to 12 while for every three or four ounces of developer a single drop of the bromide solution will suffice.

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