A SIMPLE MODE OF INTENSIFYING NEGATIVES.
Undoubtedly the best possible practice of photography is that which requires no after intensification in the production of a first-class negative. This, however, though a “consummation devoutly to be wished,” is not always attained, even by the most experienced photographer. Every operator knows that there is sometimes a condition of things that renders a simple and efficient process of intensifying afterwards indispensable.
Of all the modes of intensifying—and their name is legion—I think the readiest and most generally useful has been much neglected. The persulphate of uranium and ferridcyanide of potassium process gave wonderfully charming results. But what of that? It was completely impracticable, and a failure, in consequence of its tendency to go on increasing in intensity in the hands of the printer.
The bichloride of mercury and iodine processes, unlimited in number, also went on increasing in an unlimited degree, and no amount of “roasting” could reduce the negatives so treated to the desirable degree of transparency that would enable any printer to obtain good impressions. There is, however, one of the bichloride of mercury processes, published some years ago, which I modified so as to give the most satisfactory results. It rendered the negative sufficiently intense, and preserved the most exquisite modelling, without changing afterwards; but the process was very troublesome, and not very agreeable.
The simplest, cheapest, and most reliable process of intensifying negatives that I know of is with sulphuret of potassium (liver of sulphur) used in the following manner:—
Make a very dilute solution of sulphuret of potassium, put it into any old gutta-percha or porcelain bath; and, after the negative is developed as far as is desirable with the ordinary iron developer, fixed, and washed in the usual way, immerse the plate in that state at once into the solution of sulphuret of potassium, in the same manner as in sensitising the plate in the nitrate bath, by using a dipper, and leave it there until sufficiently intense, which is generally in about the time required for coating and sensitising another plate, so that, if the operator be working single-handed, very little, if any, time is lost in the process of intensifying.
The solution may also be flooded over the plate in the same manner as the developer, after fixing and washing as before.
When sufficiently intense, rinse the plate with water, dry, and varnish in the ordinary way. But it is best to use the intensifier in the manner first described, which is by far the most cleanly and economical plan, both in the saving of time and solution. By using it with the “bath and dipper,” it is not offensive, on account of its extreme dilution, and not being disturbed so much, or immediately under the olfactory nerves of the operator, it may be worked in the ordinary dark room with the greatest safety and convenience.