Enlarged negatives may be made on bromide paper by giving a very full exposure and developing a deep imager. After drying, wax the back of the print well and heat it over a stove until the print is thoroughly impregnated with the wax; then iron the print flat between blotting-paper. The most satisfactory method, however, 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 down to a sheet of glass coated with insoluble gelatine and developed as usual. The glass is prepared by coating it with a 10-per-cent. solution of gelatine, immersing in a 3-per-cent. solution of bichromate of potash, and exposing to the light. The carbon process gives excellent transparencies capable of rendering the finest detail. Instead of using bromide paper, the transparency is enlarged in the usual way (except that the glass side of the transparency must face the enlarging surface) on to a wet collodion plate made as under. Procure 10oz. iodised collodion, 2oz. nitrate of silver, loz. ferrous sulphate, 2oz. acetic acid, and 4oz. alcohol.

A new glass plate of the required size must be cleaned thoroughly by rubbing with alcohol, and then coated with collodion as in varnishing a negative. Directly the collodion has set, the plate may be lowered into the silver bath, which should consist of 35 gr. of silver nitrate to each 1 oz. of distilled water. If the dish containing the bath is flat and level, 25 oz. of solution can be made to suffice for a 20-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 developer until the image is well out, when the plate is immersed in a fixing bath of hypo. The developer consists of ferrous sulphate 40gr., acetic acid 20 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 successfully. The development of a 20-in. by lo-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 col-lodionising, to coat the plate with a filtered mixture of the white of one egg, 4 drops of ammonia, and lqt. of water.