The Optical Magic Lantern Journal (July 1899)

88 The Optical Magic Lantern Journal and Photographic Enlarger. landscapes, but are not so generally used as their merits deserve. There is no doubt that the great majority of | amateur slide makers use bromide or chlorobromide plates. I should think it is no exaggeration to say that they exceed all the others put together. Most makers supply plates | of two rapidities, rapid for black tones and slow for warm tones. With the rapid plates very pleasing brown colours can be obtained with a long exposure and restrained developer, and the slow series will give good warm blacks with a short exposure and quick development. For pure cold blacks the newer developers, such as metol, amidol, and rodinal, give the best results ; hydroquinone also gives a good colour, and pyro may be used where rather more warmth is preferred. The solution for developing slides must be weaker than that used for negatives, generally about half the strength, and with most plates the development must be carried further than appears necessary in the unfixed slide, as the hypo bath often has an apparently reducing effect. over the sky and high lights will be hardly visible when the slide is fixed, and can usually be ignored. shorter exposure should be given. than when using quinol or pyro; a full exposure is very likely to lead. to considerable veiling of the lights with a consequent over flattening of the slide. A safe guide in the choice of a developer is to use the one recommended by the plate maker, but I find that an average developer will suit most of the kinds of plates that I have tried. The great thing to learn is when to stop development. It is not a thing to be learned from books: or verbal instruction, but comes with practice. There are far more plates spoiled after they go into the developing dish than by the exposure, and among beginners, at any rate, the fault is in not developing long enough. The production of brown tones is dependent on long exposure and restrained development ; the longer the exposure and development, the warmer is the tone. The favourite developers for these colours are hydroquinone and pyro, used with the addition of considerable amounts of bromide and sometimes ammonium carbonate. For my own use I prefer pyro ammonia, Thomas’s old formula, made up of pyro sulphite 10 per cent. solution 30 minims, ammonium bromide. 43 grains, ammonium carbonate 44 grains, ammonia 8.803 minims, water to .2 ounces; for redder tones Any slight veil | With the newer developers a rather | more bromide and ammonium carbonate is added, with, of course, increased exposure. There is some difficulty at first in judging the depth to which development should be carried, and ‘it varies greatly with the make of plate used. The appearance of a_fully-developed Ilford special plate treated for brown tone would be quite different from a Thomas’s plate developed for the same colour. The Ilford plate should look rather weak, and the other make fully dense; in the first case you have a bromide plate, and in the other, I believe, a mixture of chloride and bromide emulsion ; but, as I said before when speaking of black tones, do not stop development too soon, for the -. richness of the colour depends largely on the time required to obtain density ; a slide that has developed too quickly is often a poor and rusty brown colour. A good slide will often take 10 minutes or more, and, if the acid fixing bath is used, it will clear away any slight stain there may be from the pyro. With hydroquinone there is no fear of staining, and the same developer may be safely used for two or three plates; but care must be taken that the exposure is sufficient, or there is some risk of the slide being rather hard ; the colours obtainable are very good. Thomas’s.is a useful formula, and is as follows :— No. 1 Soxuriox. Hydroquinone 160 grs. Sodium sulphite 2 ozs. Citric acid .. ee 60 gra. Potassium bromide . 40 gre. Water to . 20 ozs. No. 2 Sonution. Sodium hydrate is 160 gra. Water to 20 ozs. For black tones take 4 ounce of each and 1 ounce of water ; for brown, add 14 grains each of ammonium bromide and ammonium carbonate, and for warmer tones, increase the amount up to 9 or 1O grains of each to the 2 ounces of developer; the full amounts of restrainer will require a very long exposure—about five or six times as much as would be given for a rather cold brown, and will probably take a quarter of an hour to develop. In very cold weather it 1s advisable to use a little warm water in making up the developing solution, as many developers act very slowly when very cold; pyro is, however, to a large extent an exception. If a slide gains density very slowly in cold weather, it is a useful but unscientific dodge to rest the dish on the top of the dark-room lamp for a minute or two so as to raise the temperature slightly—I have often saved slides