ENLARGED _NEGATIVES BY THE WET COLLODION PROCESS.
The most satisfactory method, however, of producing a big negative when a carbon enlargement is to be made (and the method employed by all professional workers) is as follows: From the small negative a carbon print is first made on special transparency tissue, squeegeed clown to a sheet of glass coated with in soluble gelatine and developed as usual. The glass is prepared by coating it with a 10 per cent. solution of gelatine, im mersing in a 3 per cent. solution of hichro mate of potash, and exposing to the light. The carbon process gives excellent trans parencies capable of rendering the finest detail. The transparency is enlarged in the usual way, except that, if made by the single transfer process. the glass side of the transparency must face the enlarging surface, on to a wet collo dion plate made as under : Procure or make (see p. 74) 10 oz. of pure iodised collodion, 2 oz. nitrate of silver, 1 oz. of ferrous sulphate. 2 oz. acetic acid, and -1 oz. alcohol. A new glass plate of the size of the required negative must be thoroughly cleaned by rubbing with alcohol, and then coating with collodion as in varnishing a negative. Directly the collodion has set, the plate may he lowered into the silver bath, which should consist of gr. of silver nitrate to each 1 oz. of distilled water. If the dish con
taining the bath is flat and level, 25 oz. of solution can be made to suffice for a •0-in. by 15-in. plate. _After exposure (care being taken to guard the wet film from dust and to keep the drained corner at the lower level throughout), the still wet plate is flowed over with the tie veloper until the image is well out, when the plate is immersed in a fixing bath of hypo. The developer consists of ferrous sulphate 4o gr., acetic acid 2o minims, to each ounce of distilled water, with sufficient alcohol to make it flow easily. Considerable practice is necessary before plates of this size can be worked snecesr, fully. The development of a by 15-in. plate is best carried out in a dish, instead of holding the plate in the hand as in small work. Porcelain dishes larger than the largest plates likely to be used must be provided, and the one containing the silver bath must be retained for that especial purpose. Collodion film, unlike gelatine, is extremely tender, and will not bear touching ; even a strong flow of water is sufficient to disturb it. It is advisable. though not absolutely necessary, before collodionising, to coat the plate with the white of one egg, 4 drops of ammonia, and 1 qt. of water mixed well and filtered.