NEGATIVE, ENLARGING.— —The crudest and least recommendable method of enlarging a gelatine negative is, to simply soak it in water containing about one-twelfth of its volume of strong liquid ammonia. It two or three hours the film will be found to have frilled from the plate and extended to a considerable extent. If the film is a thick one, the enlargement may be as much as two diameters; but if it is not sufficiently distended, small quantities of hot water should be added to the bath. The loose distended film floating in the bath is then caught upon a large piece of glass. It can, of course, be reversed, if required. This method of enlarging a negative is, how ever, a very uncertain one, and can only be used with great danger of destroying the negative itself.
The two commonest methods of enlarging negatives are first the production of a positive transparency by contact from the negative and an enlargement made from this; and second an enlarged transparency is made from the small negative, and the large negative made from this by contact. There are plenty of advocates of both methods, but the majority of advantages are probably in the method of producing the enlargement direct from the negative—that is to say, making a large transparency, and printing the negative by contact. In this manner the defects of the positive are not enlarged, and it will be found much easier to eliminate defects on a large than on a small transparency. The large transparency* offers particular facilities for producing
one or many enlarged negatives by a printing-out process, as, for instance, on albumenized silver paper after Valentine Blanchard's method. Excellent results can thus be obtained, the sensitive paper is exposed somewhat longer than it would a positive print, then washed, fixed, dried and waxed. No toning is necessary, and such paper negatives appear on the whole to be more stable than ordinary toned prints. If necessary, new negatives can easily be made, and each is as exact a reproduction of the first as possible. The various methods of making a transparency are given under that heading.
The negative or transparency to be enlarged must be illuminated equally all over. It will then only be necessary to expose a large plate in the camera to obtain the desired result. Those, however, who do not possess a large camera must enlarge on a dry plate, in just the same way as on bromide or other enlarging paper. The image is thrown by the optical lantern on to the easel, or screen, and focussed. A slight alteration must then be made in this to allow for the thickness of the plate, which is then fixed in position and exposed.