When the focussing is accurately performed the cap is placed on the lens, the drawing-paper is removed, and its place is taken by a piece of gelatino-bromide paper, when the exposure is made. As the exposure may vary according to the lens used, and the distance between the lens and the sensitive paper, from a few seconds to many minutes, it is best to make a trial exposure first, using only a small piece of paper, which is at once developed.
When the exposure is over the enlarged print may be developed. This is done in almost precisely the same way as a plate is developed, ferrous oxalate being used. The directions which are issued with the paper should be implicitly followed. If the enlargement be of moderate size, say not more than fifteen inches by twelve, it may be developed in a dish; if it is larger it is usual to construct a dish out of the paper itself, which is laid on a board or piece of plate-glass, and the edges are carefully turned up.
After development is complete the print is washed. Then it is treated with the precise same alum solu tion which is recommended for negatives, is washed and is fixed with the negative-fixing solution. It is once more thoroughly washed, and when dried is finished.
The remarks which we made with regard to the use of opal glass for positives when treating on the alpha paper and plates (see p. 180) hold equally good in the case of enlargements. The Britannia argeutic bromide opal plates are made specially for the production of enlargements, and very beautiful results can be got with them.
It will be seen that for enlarging in this manner a separate operation with the enlarging apparatus has to be gone through for each negative which is required. This is very troublesome if many enlarged prints are wanted. Moreover, the colour of the gelatino-bromide print, which is of an engraving black, although it is liked by many, is by some thought not so good as that of a print on albumenised paper. If an enlargement on this latter is required, it is necessary to take an enlarged negative, usually on glass; and if many enlarge ments of the same subject arc required, it is best to do the same.
There are two ways in which an enlarged negative may be got. Before describing them we must mention that a transparency is a picture on glass like a negative, but with the shades correct instead of reversed. Such may be got by simply placing a sensitive plate in contact with a negative, and allowing the light from a gas burner or lamp at a distance of a couple of feet or so to shine through the negative for a few seconds. Develop ment is performed as usual.
If a glass plate take the place of the sensitive paper mentioned already, an enlarged transparency will result. To get an enlarged negative we may either take a trans parency by contact from the small negative, and place this transparency in the enlarging apparatus, and thence get an enlarged negative, or we may place the small negative in the apparatus, and get from it an enlarged transparency, from which an enlarged negative may be got by contact.
The former plan has the advantage of economy,—one large and one small plate being used, whereas in the latter two large plates are used. There are, however, advantages in the latter case which more than counter balance the slight additional expense. In the first place
it is likely that the final negative will be sharper, but, besides this, there is offered an excellent opportunity for retouching which would not otherwise be afforded. If our chapter on retouching be considered, it will be seen that the only defects which can be eradicated are those which appear too transparent in the negative and too dark in the print. Such as appear too dense in the negative and too light in the print can be corrected only by manipulating each separate print. When, how ever, we have an enlarged transparency as well as an enlarged print we can eradicate defects of both natures. It might be supposed that the small transparency would serve as well for retouching on as the large one ; but it must be borne in mind that the marks of the pencil on the small transparency, when magnified in the enlarged negative, would appear excessively coarse.
Taking all this into consideration, we describe the process for getting an enlarged negative by means of an enlarged transparency.
The plates used are the same as those employed for landscape work. The best thing to focus on is a piece of glass whitened by rubbing a piece of putty on it. This is fixed to the easel by drawing-pins, the edges of the pin-heads being made to clip the glass plate. The plate is of the same size as the enlarged transparency and negative are to be, and its thickness will allow for the thickness of the former of these after focussing. The small negative is placed in the lantern, and focussing is performed exactly as for the paper.
The whitened glass is removed, and a sensitive plate takes its place. The sensitiveness of this will be found to be much greater than that of the paper, probably five or six times as great. On the other hand, the time allowed must be such as to give (allowing for difference of sensitiveness) a far more complete exposure. Where a positive is desired the highest lights must remain pure white. When a transparency is wanted it is necessary to get printing density in all the details of the highest lights. To make sure of this we must give such an exposure that no part will remain quite white. The exposure will therefore, allowing for the difference of sensitiveness, most likely be about one-half that required for a positive on paper. The development is performed exactly as for a landscape negative. If ferrous oxalate developer be used the transparency itself will be very pleasing in appearance, and may be kept to hang up against a window, so as to be looked through.
After it is dry, and any retouching which is required is done, a negative is taken from it by contact. It is best to place the transparency and the negative both in a printing frame so as to ensure there being no motion between the two. The exposure required will average about ten or fifteen seconds at a distance of four feet from an ordinary 15-candle gas-burner or good paraffin lamp. The development is conducted precisely as for a land scape negative, and the negative should not be different in appearance from one taken direct, except on very close examination. It is treated precisely as an ordinary negative.