A Manual of Photographic Chemistry, Including the Practice of the Collodion Process

by T. Frederick Hardwich

The colour of Positives developed upon Iodide of Silver is not agreeable, and they become blue and inky when toned with gold. By fixing the proof in Hyposulphite of Soda which has been long used and has acquired sulphuretting properties, the tint is much improved; but the permanency of the Print under unfavourable conditions is lessened by adopting that mode of toning.

A NEGATIVE PRINTING PROCESS UPON BROMIDE OF SILVER.

By substituting the Bromide for the Iodide of Silver in the above process, the proportions and details of manipulation being in other respects the same, a more agreeable colour is obtained.

Paper prepared with Bromide of Silver is less sensitive than the Iodide, but an exposure of one minute (in the printing frame) will usually be sufficient even on a dull day. The image is nearly latent, but sometimes a very faint outline of the darkest shadows can be seen. The proportion of Bromide used is likely to influence this point; the sensitiveness being diminished, but the image showing more of the details before development, when the quantity of the Silver Salt is reduced to a minimum.

Either English or French papers may be used, but in the latter case the Bromide should be dissolved in Serum of Milk ([p. 262]), or it will be difficult to obtain a good surface picture. The proportion of Bromide may be five grains to the ounce of Serum.

These proofs, even when simply fixed in plain Hyposulphite of Soda, are superior in colour to the Positives printed by the last formula upon Iodide of Silver; and the permanency is very great if the development be sufficiently pushed. The use of the Serum of Milk gives an advantage in resisting the oxidizing influences to which Positives are liable to be exposed ([p. 150]).

GENERAL REMARKS ON NEGATIVE PRINTING.

Printing by development should not be attempted until the manipulation of the ordinary process by direct exposure to light has been acquired.

Perfect cleanliness is essential. The salting or iodizing solution and the Aceto-Nitrate Bath must be filtered clear, as the effect of small suspended particles in producing spots is more seen when the image is brought out by a developer.

It will be necessary to be far more careful in excluding white light than in the ordinary process; and when Iodide of Silver is used, all the precautions required in the case of Collodion Negatives must be taken.