PYRO. AND AMMONIA. STOCK SOLUTIONS.
No. 1.—Liquor ammonite, SSO° 1?, oz.
Potassium bromide, ... S drs.
Water ... 2.—Pyrogallic acid ... 1 oz.
Citric acid ... 2 drs.
Water ...... Or.
• • • For use, take 1 oz. each of No. 1 and No. 2, separately, and dilute with 15 oz. of water. Label these solutions A and B respectively. Equal parts of A and B are taken for development. The ammonia solution must be kept well corked, or it will lose strength by evaporation. The strong ammonia requires to be opened with care, and must not be exposed to a sudden rise of temperatiire, or an ex plosion may result. In making up No. 2, dissolve the pyro. in the water first, and acid the acid last.
For use, take equal parts of No. 1 and No. 2 for normal exposures. This is a rapid developer, and gives excellent detail ; be sides being useful for all ordinary purposes, it is especially adapted for hand-camera work.
Acetone was introduced by Messrs. Lu miere as a substitute for alkali, the above being the formula recommended by them. It is a good all-round developer, clean and efficient in action.
The hydroquinone must be completely solved before the sulphite is added. For use, take equal parts of No. 1 and No. 2.
This solution will not keep more than twenty-four hours after preparation. fly droquinone is noted for its density-giving properties, and is invaluable where bright ness and vigour are desired, as in copying, making transparencies and lantern-slides, photo-mechanical work, etc. For work where greater softness is necessary, a com bination of hydroquinone and metol is to be preferred. Negatives developed with hydroquinone lose more in fixing than usual, and this must be allowed for. The developer is also extremely slow at a low temperature.
This formula will not keep quite so we as the two-solution developer.
For use, take 1 part developer and 1 par water. Two drops of a 10 per cent. solu tion of potassium bromide should be adde to each ounce of the diluted developer except in cases of under-exposure or where special softness is desired. This level open is admirably suited for hand-camer exposures, as well as for bromide and gas light papers, giving with the latter beauti ful velvety-black prints ; it is also well adapted for ordinary work of all descrip tions.
For use, take equal parts of No. 1 and No. 2. Potassium carbonate may be sub stituted for the sodium carbonate if de sired, the proportions being the same as before. .Metol is an extremely active developer, and produces soft, delicate negatives. It has the peculiarity of bring ing out the detail of the negative first. and gradually building up the density. It is equally suitable for plates, bromide prints, and lantern-slides. This developer is of
especial value where detail rather than contrast is desired. Where prolonged development is required, a little potassium bromide should be added ; but for average work this is unnecessary. A combination of metol and hydroquinone gives the den sity-forming character of the latter com bined with the detail-giving qualities of metol. With some persons, metol pro duces a disagreeable eruption of the skin, if used to any extent ; but this rarely happens.
This gives the greatest degree of control possible with a two-solution developer. For use with normal exposures, take 1 oz. of No. 1 and 3 oz. of No. 2. For over-' exposure use less of No. 2, or add a few' drops of bromide solution ; for under-ex posure, use more of No. 2. The metol and hydroquinone developer, like most of the non-staining reducers, may be used repeat edly, but becomes gradually slower with use.
For use with normal exposures, take 4 oz. of No. 1, and add gradually 1 oz. of No. 2. For a restrainer, a 10 per cent. solution of potassium bromide may be employed, 10 minims of this added to the mixed devel oper being a distinct improvement if the plate is fully exposed. As an accelerator, a solution of hypo. I. part to 25 parts of water is useful. In cases of under-expo sure, from 3 to 20 minims of the latter may be added to each ounce of mixed devel oper. It is better, however, to avoid the use of hypo. if possible. The ferrous oxalate developer, as already stated, will only work satisfactorily when in an acid condition. It has the great merit of not reducing any portions of the silver bromide on the plate except those which have been exposed to the action of light ; that is to say, it has no fogging effect. On this account, it is largely used in testing the speed of plates, and for similar scientific purposes. It has the defect of not keeping very well, and it is comparatively slow. The oxalate solution should be dissolved in hot water, and the iron in lukewarm water. The latter solution has the worst keeping properties, and quickly spoils on exposure to air. To avoid this, it should he kept in a number of small bottles, filled up to the cork, instead of in one large bottle. If this plan is adopted, and the corks are covered with wax, the solution will keep some time. With this developer a clearing bath is necessary before fixing, and it is advantageous to use another clearing bath after fixing. The object of this is to prevent the formation of various precipitates likely to occur if the water lime, and in some other circum stances.