DEVELOPMENT OF CRISTOID FILMS.
The Sandell Cristoid Film possesses several special It is made up of two distinct layers of emulsion, of different speeds, and consists of gelatine alone without any support or base. The com bination of a slow and a rapid emulsion allows great latitude of exposure, and halation is almost impossible. The film may be obtained either in rolls or cut to any ordinary plate size. Before develop minutes, according to the temperature. In cold weather, the formalin bath is un necessary. After hardening, the film is rinsed; and placed in the developer, being moved about in the same way as before.
A liberal quantity of developer should be used to ensure perfect immersion. Any developer may be used, but pyrocatechin is recommended, rodinal and synthol also being very satisfactory. Development should be continued until the negative no longer gains in density. The film is then rinsed and fixed in a hypo. bath of double the ordinary strength. The most con venient method is to place the films in a jar or jug containing the fixing solution, ment, the film is hardened in a formalin solution in the proportion of 2 oz. of formalin (Schering.) to 2 oz. of water. This may be used repeatedly, until it becomes too weak. The film should be unrolled, and folded across the dish from end to end, as shown by Fig. 200 ; taking care, how ever, that each part of the film is immersed before another portion is folded over it. Move the film about rapidly, so as to ensure even action of the solution. If one fold is found to stick to another, pull it carefully apart, and keep circulating the film with the tips of the fingers, as shown by Fig. 201. The film should be taken out
as soon as it becomes perfectly flexible, the time varying from one to three and to stir them up for a few seconds. Fixing will probably be complete in about two minutes, but the films should in no case be removed until perfectly free from white unfixed silver. They should be kept in the dark-room until this is accom plished, and are then washed as usual. The Cristoid film is a favourite with archi tectural workers, and in all cases where halation is likely to occur. The double film of different rapidities affords a re mailable compensation for even extreme errors of exposure. It might be thought that the unsupported gelatine film would requirb great care in manipulation, but such is not by any means the case. After treatment with formalin as already directed, the film will be sufficiently hardened to stand any amount of handling.
feetly clean piece of glass, ferrotype plate, or pulp slab. The negative side, which is darker, should be uppermost. In warm weather, the films should be treated with a glycerine bath before squeegeeing, in the proportion of s oz. of glycerine to 40 oz. of water. This may be used re peatedly. In any ease, the film is left flat on the glass for a short time, and then stood up to dry in a suitable place. Care should be taken that no draught reaches it in the process of drying. When quite dry, a knife is passed under one edge, and the film carefully stripped off.