I would also recommend that the paper should be excited upon the morning of the day upon which it is intended to be used; no doubt the longer it is kept, the less active and less certain it becomes. I have, however, used it successfully eight days after excitement, and have a good negative produced at that length of time. The general medium time of exposure required is five minutes. In the negatives exhibited, the time has varied from three minutes to eight, the latter being when the day was very dull.
The pictures should be developed by equal quantities of the aceto-nitrate of silver and the saturated solution of gallic acid, which are to be mixed and immediately applied to the exposed surface. This may be done several hours after the pictures have been removed from the camera. Care should be taken that the back of the picture does not become wetted, as this is apt to produce a stain which may spoil the printing of the positive.
If upon the removal of the paper from the dark frame, the picture is very apparent, by first applying little gallic acid, and immediately afterwards the mixed solutions, less likelihood is incurred of staining the negative, which will be more evenly and intensely developed. If a browning take place, a few drops of strong acetic acid will generally check it.
Should the picture be very tardy, either from an insufficient exposure, want of light, or other cause, a few drops of a solution of pyrogallic acid, made with 3 grains to the ounce of water, and a drachm of acetic acid, will act very beneficially. It sometimes gives an unpleasant redness upon the surface, but produces great intensity upon looking through it. Until the pyrogallic solution was added, there was scarcely anything visible upon the specimen exhibited, the failure having in the first instance happened from the badness of the iodized paper.
As soon as the picture is sufficiently developed it should be placed in water, which should be changed once or twice; after soaking for a short time, say half an hour, it may be pinned up and dried, or it may at once be placed in a solution almost saturated, or quite so, of hyposulphite of soda, remaining there no longer than is needful for the entire removal of the iodide, which is known by the disappearance of the yellow colour.
When travelling it is often desirable to avoid using the hyposulphite, for many reasons (besides that of getting rid of extra chemicals), and it may be relied on that negatives will keep even under exposure to light for a very long time. I have kept some for several weeks, and I believe Mr. Rosling has kept them for some months.
The hyposulphite, lastly, should be effectually removed from the negative by soaking in water, which should be frequently changed.
Some prefer to use the hypo, quite hot, or even boiling, as thereby the size of the paper is removed, allowing of its being afterwards readily waxed.[[9]] I have always found that pouring a little boiling water upon the paper effectually accomplishes the object; some negatives will readily wax even when the size is not removed. A box iron very hot is best for the purpose; but the most important thing to attend to is that the paper should be perfectly dry, and it should therefore be passed between blotting-paper and well ironed before the wax is applied. Negatives will even attract moisture from the atmosphere, and therefore this process should at all times be resorted to immediately before the application of the wax.
Some photographers prefer, instead of using wax, to apply a solution of Canada balsam in spirits of turpentine. This certainly adds much to the transparency of the negative; and, in some instances, may be very desirable. Even in so simple a thing as white wax, there is much
variety; some forming little flocculent appearances on the paper, which is not the case with other samples. Probably it may be adulterated with stearine, and other substances producing this difference.