| A | ||
| Hydroquinone | 80 | grains. |
| Soda sulphite | 1 | ounce. |
| Potassium bromide | 15 | grains. |
| Water | 10 | ounces. |
| B | ||
| Caustic soda | 80 | grains. |
| Water | 10 | ozs. |
The developing solution consists of equal parts of A and B, and the plate may be fully developed in about two to three minutes.
It has already been stated that in order to obtain really warm red or reddish tones by development, it is necessary to give very long exposure, and to use a developer very much restrained. It is further found that carbonate of ammonia has a considerable effect in reddening the developed image, and so we now come to procedure based on these lines. Carbonate of ammonia is found in commerce in the shape of "chunks" more or less square. If one of these is pared with a knife—unless the sample is quite fresh—the outside will be found to be a soft amorphous powder, the inside a clear, very hard crystal; the clear crystal is in development an "accelerator," though a very weak one, the outside substance is a restrainer. Probably both the inside—sesquicarbonate—and the outside—bicarbonate—are useful, and the best plan is to make a ten per cent. solution of the substance as obtained from a good chemist—not druggist. Of this solution one grain of the salt is represented by ten minims. If now we take an ounce of A, and one of B of the last formula, and if we add to the ounce of A 3 grains of ammonium bromide, and to the ounce of B 3 grains of ammonium carbonate, and if we have given a proper exposure and develop with equal parts of the A and B modified as above, we shall get a slide of rich chocolate colour; and if we double the proportions of carbonate and bromide, and expose still longer, we shall get a slide still ruddier in tone, even to red. But there is always danger of fog, and of clogged shadows, and this must be reckoned with. There is a more certain and less dangerous way of getting handsome tones, which shall be described presently.
Gelatine slides are always fixed in hyposulphite of soda, about one part by weight to six parts of water; after this they must be well washed, say five minutes under a good rose tap, or in many changes of water in a dish for an hour, and every slide should be treated with a saturated solution of potash alum, of which each pint should contain a dram of hydrochloric acid.
Very many, if not most, slides are all the better for just a touch of a "reducer" such as follows:—The ordinary "hypo." solution is weakened with about four times its measure of water, and the plate is soaked for a minute in this. A few drops of a ten per cent. solution of potassium ferricyanide are put into the measure, and the hypo. mixed with it, and the whole allowed to work on the plate for a short time, carefully watched. Of course a weak slide must not be thus treated, but it is often a good plan to develop slides to such a point that they will permit of this treatment.
On the other hand it is often advisable to keep a slide thin in development, for instance, when the negative wants pluck, and intensification is indicated; or when we wish a good warm tone after a "black" developer such as our metol formula: a good average treatment is as follows:—
Take half an ounce each of ammonium chloride and mercury bichloride and dissolve in 16 ounces of water, soak the slide in this till it is bleached. Wash well and treat with weak liquid ammonia, or a solution of soda sulphite, or of metabisulphite of potash, or fresh lime water. This will strengthen the slide and give it in most cases a fine rich colour. It is important to let these solutions act thoroughly, and not to stop the action half-way. The writer considers this the best and safest way to obtain warm tones, the reader may find out for himself which of these solutions produces the tones he chiefly affects.
Crystal varnish is not wasted even on a gelatine slide.
In conclusion, it must be realized that the screen-image is a greatly enlarged edition of the slide-image; any small defect on the slide is a huge one on the screen. Consequently the slide-maker must sedulously cultivate cleanliness and manipulative care.
Andrew Pringle.