The bath referred to is prepared by dissolving in ten ounces of water one ounce of sodium bisulphite; in another ten ounces of water four ounces of sodium hyposulphite are dissolved ; and then, while stirring, the bisulphite solution is poured slowly into the soda solution. When mixed, the formula will stand thus :

On removing the slide from the faxing bath and examining it before a piece of opal or ground glass, it should appear "crisp" without any appearance of "inkiness" in the shadows, and when laid upon a sheet of white paper the extreme high lights should have the appearance of being bare glass.

Amidol Developer (For Warm Black)

The exposure for warm black colors when using the above developer will be about double the exposure required for black, and development will be rather slower; it should not be carried so far, however. When the production of warm colors is attempted with gelantine plates, it is better to adopt pyrogallol as the developer. Now that warm colors cannot be obtained with the modern reducing agents, but "pyro" and ammonia undoubtedly produce them with greater facility than do the others. The subjoined formula has given in my hands very good browns with above five times the exposure needful for blacks. With some plates, to produce brown colors, it may be necessary to add more bromide.

Pyrogallol Developer (For Brown.)

Equal parts of each are taken to develop.

It will be noticed when developing for warm colors that the image develops in a manner different from a black colored image. With black images the gradations appear crisply defined on the surface of the film, but with warm colored images the picture seems buried in the film, and is only seen when examining the plate by transmitted light. This appearance is rather puzzling to the novice, and misleads him into giving greater density to the plate than is desirable. Only experience can enable him to judge when correct opacity has been reached, but he will find, where warm colors are in question, that a very small amount of apparent density will prove on fixing to have been ample.

The development of lantern plates in the production of warm colors is oftentimes a tedious operation, requiring perhaps ten or fifteen minutes, and there seems no way of curtailing and retaining at the same time the quality of the image. Loss of time may be prevented by using a grooved tank and leaving the plates to develop while other exposures are being made. Development is so slow that over development need never be below 65° F. Should warmer colors than those given by the above developer be required, they may be obtained by adding to each ounce of the mixed developer twenty or thirty minims of a ten per cent solution of ammonium carbonate. It has been stated, but not on sufficiently good authority, that the use of carbonate causes fading. In place of adding the carbonate as a ten per cent solution, it may be combined with the developer in bulk, in which case the following formula is a convenient one :

Phrogalloll Developer (For Warm Brown.)

Equal parts of each are taken to develop.

The formula given in this chapter will cover the whole field of the development of gelatine lantern slides. Success in lantern slide work is due not so much to any special formula as to continued practice on the part of the operator. The production of first class slides as regards crisp-ness, color, and exact density is not, in my experience, too easy of attainment, nor does there appear to be any "royal road" to such an end.