This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
798. There are times when one is well equipped for making good small negatives, but, has not the necessary apparatus for making large negatives. Professionals, very frequently, are handicapped for space sufficient to operate a large camera, and, in consequence, can only make small size negatives, notwithstanding the fact that they frequently have calls for larger prints from the same negative.
799. The amateur, too, very frequently has small negatives which he would like very much better if they were double or triple the size. A Bromide enlargement from the smaller negative would, in some cases, answer for a single print, or even two or three prints; but there are times when the prints are desired made on platinum, or some other printing-out paper. It is then absolutely necessary to make contact prints, and, therefore, they must be made from an enlarged negative. To meet these requirements this instruction is prepared.
Methods. Two methods for making enlarged negatives will be described-one worked in the open light, using a large camera containing a long bellows; the other in the regular dark-room, or a small room made absolutely dark, employing the same method as for making Bromide enlargements, the dark-room serving as a large camera. The first method is employed in studios, and where large cameras are used, therefore, it will be described first.
The Transparency. No matter which method is employed, for all negative enlargements a positive transparency must first be made; then from this transparency make the negative. This can be done in two ways: Making the transparency by contact, then making the enlarged negative from the small transparency; or, making an enlarged transparency from the small negative, then making the large negative, by contact, from the enlarged transparency.
802. The latter method has advantages and may give better results, yet it is more expensive, as it requires two large plates. The former method requires only one large plate and one small one the size of the original. Therefore, the first method is generally used, and is recommended for your first experiments at least.
Kind Of Plates To Use. For making the transparency the best results are produced by the use of a special transparency plate, or an ordinary slow plate. Ordinary rapid plates can be used, but they will require more exactness in the exposure. For making the enlarged negative from the transparency, it is not as necessary to have a slow plate as it is in making the transparency, for upon the quality of the transparency depends the result of the enlarged negative.
Quality Of The Emulsion. Regular transparency plates are of a finer emulsion, and there is less danger of grain showing in the enlargement. The grain of an ordinary plate, when enlarged, is apt to make the enlarged negative appear coarse; the resulting print, therefore, will likely have the appearance of being made from a copy. Even slow plates possess some grain, and if an average rapid plate is used for making the intermediate contact transparency, the grain of the original negative is reproduced in the transparency, and in turn, the grain of the transparency is reproduced in the enlarged negative.