The nature of the developer used has, of course, some influence on the sensitiveness of the plates; but in the above cases it is assumed that oxalate developer, without any addition, is used; or pyro., to which ammonia is added at intervals of about thirty seconds, so as to produce a slight tendency to fog; the time of development being from three to four minutes. The numbers are supposed to be read after fixation, the plate being held against the sky.
Schumann’s statement that a gelatino bromide plate is less sensitive when developed at 30 deg. C. than when developed at 5 deg., is contested; the more recent investigations of Dr. Eder serving to demonstrate that a developer at a moderate high temperature acts very much more rapidly than when the temperature is low; but when a sufficient time is allowed for each developer to thoroughly penetrate the film, the difference becomes less apparent. Here are examples:
Temperature of developer 4-8 deg. C. 16-17 deg. C. 26-28 deg. C. Time of development 1 min. 3 deg. W. 8 deg. W. 13 deg. W. " " 2 min. 91/2 deg. W. 10 deg. W. 15 deg. W.
Temperature of developer 1-2 deg. C. 26-28 deg. C. Time of development 1/4 min. 6 deg. W. 10 deg. W. " " 3 min. 14 deg. W. 15 deg. W.
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By MAJOR WATERHOUSE.
The collodion process is still preferred for reproducing black and white designs, drawings, engravings, etc., where very dense negatives are desirable. The fixed and washed plate is put in a bath of bromide of copper (ten per cent. solution); the film whitens immediately, and when the color is even all over, the plate is taken out and plunged into a bath of the ordinary ferrous oxalate developer. It takes a dark olive tint, which is very non-actinic, the shadows meanwhile remaining very clear.—Photo. News.
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By this time of the year I have no doubt many, both amateur and professional photographers, are either contemplating or are actually at work making their stock of plates for the coming season, and it is to be hoped that we shall have more favorable weather than we had last year.