The conditions under which photographic plates are exposed and developed vary so greatly that rarely is it possible to secure a perfectly satisfactory negative. Some will be thin in opacity, with contrasts so weak that the prints made therefrom will be soft and flat, the remedy for which is Intensification. Or the negative may have the reverse of these faults: have too great opacity, or give excessive contrasts, for which the remedy is Reduction. The former faults usually result from over-exposure and under-development; the latter from under-exposure and over-development, or the use of a developer which worked too rapidly, producing opacity without detail.

In Intensification the object sought is to increase the opacity in such a way as to give deeper and sharper contrasts in the print without the loss of detail, and should immediately follow development when possible. Old negatives can be successfully treated, however, and are good subjects for study in learning this work. Having decided that it is desirable to intensify a negative, the first thing necessary is to give it a thorough washing, whether it be old or newly made. It is absolutely necessary to good results that all "hypo" and other free chemicals be completely removed ; also that the negative has been properly fixed. If any uncertainty exists on this point it is advisable to refix in a fresh fixing solution ; previous to which the negative, if an old one, should be soaked in water for a few minutes, to soften the film. After fixing, again wash in running water until all traces of hypo are removed. A half hour will be none too long a time for this washing.

There are numerous formulas for accomplishing the desired result, but the one here given is reliable, and will give a good insight into the process, and enable other formulas to be tried when desired. The first part of the work consists in bleaching the negative, which is done with a saturated solution of mercuric chloride (corrosive sublimate, Poison). In warm weather, or if the negative does not require to be much intensified, the strength of the solution may be reduced. A few trials will soon enable the worker to determine the most suitable strength to be used. In bleaching, the film will gradually whiten, and thig should be continued until the under side of the film is affected. When bleaching has been carried far enough, the negative should be well washed in cooled boiled or distilled water, remaining in the last change of water for a few minutes soaking, When washed, the film is again blackened by immersing in a solution made as follows : To five ounces of a saturated solution of potassium oxalate, to which has been added a few drops of oxalic acid, add one ounce of a saturated solution of ferrous sulphate, and then add three ounces of distilled water. This solution gives considerable density, and has the advantage that it may be repeated if desirable to do so.

Those who do not care to prepare their own solutions may purchase of photographic supply dealers prepared solutions for this work, which will give good results and improve many a negative that would otherwise be of but little value.

After the process has become familiar, it may be utilized for improving parts of a negative by local application with a soft brush. Considerable skill is required, however, to do this satisfactorily.

Reduction is the reverse of the above process. Here the desire is to remove the surplus density, to render the contrasts more subdued and bring out detail. It is especially valuable for lantern slides and for clearing foggy negatives. In this work, with the formula given below, hypo is very objectionable, and the preliminary washing to remove it must not be omitted. If reduction immediately follows development, which is desirable, as the film is then well moistened, the washing should be thorough enough to remove all traces of hypo. If it be an old negative, it should be soaked in water until the film is thoroughly moist, and all hypo removed.

The reducing agent recommended to amateur photographers, and especially the beginner, is a three per cent solution of persulphate of ammonium, or say fifteen grains to each ounce of water. When reduction has been carried to the desired point, the plate is rinsed in water and then immersed for a short time in a ten per cent solution of sulphite of soda, followed by a good washing.

This reducer has the peculiar property of working more rapidly on the denser portions of the plate than on the thinner parts, just what is usually desired. With it clouds, draperies and similar details that are often lost, can be restored, greatly enhancing the printing qualities of a plate.

As persulphate of ammonium is quite unstable, it should be prepared only a short time before use, and worked under a subdued light. There are other formulas which have their special uses, a knowledge of which is desirable as progress is made. It will need but little experience to show their value to the photographer who is desirous of producing good work, and willing to do some experimenting to achieve it.