It is a well-known fact that small quantities of silver chloride are soluble in ammonia, as well as in the chlorides of sodium, ammonium, etc, which, though solvents, are not sufficiently powerful to be used as fixing agents for silver prints. Being engaged in the production of transparencies on glass by the aid of the collodio-chloride process, Dr. Liesegang was struck by the thin layer of chloride and citrate of silver contained in the films, and at once tried the action of the above-named solvents on them. Liquid ammonia cleared the films immediately; a concentrated solution of common salt took about 5 minutes to dissolve the whitish film, the chloride disappearing before the citrate. He next tried to fix un-toned collodio-chloride prints upon paper in the same way. Ammonia has the same effect as the usual 5 per cent. solution of hyposulphite, but one cannot think of using it in large quantities in open trays, because of its fumes. Solution (concentrated) of sodium chloride is a little slow in action. He therefore tried a saturated solution of ammonium chloride, in which he left the prints for an hour. It may be that a shorter time is sufficient, or that longer soaking is necessary, but observations led him to think that one hour is a safe time.
The prints came out of the bath with the same brownish-yellow colour which also the hyposulphite imparts on them. He washed the prints for one minute under the tap, dried them and exposed them - one half being covered with black paper - to the light. Till now they have had only a few hours of sunshine and 10 days of diffused light; not a trace of difference is observable in the protected and the exposed parts. Of course, this time is not at all sufficient to prove that the fixing is perfect. He next toned a batch of prints in an old toning bath of soda tungstate, very weak in gold, for the usual time of 10 minutes, and kept them for an hour in the ammonium chloride. After drying, they had an unpleasant slate-blue colour, showing that too much gold had been deposited on them. He therefore prepared another batch of prints, which he left only one minute in the gold bath; in the chloride bath they took a vigorous purplish-brown colour, but showed to be somewhat over-exposed, although he had taken care to print less than for hypo fixing. Now, if this way of fixing prints should prove to be safe - which only time can teach us - we shall have the advantage of doing away with hyposulphite, of using less gold for toning, and shortening the time of printing.
Comparing the prints with others fixed with hyposulphite, he finds that the finest half-tones are better preserved, and that from under-exposed negatives better results are to be ob-tained. If the ammonium chloride do not sufficiently fix the prints, you may succeed by adding to it some ammonia. The fixing might be done in the upright vessels in which the prints are hung.
Dr. Liesegang also tried to fix bromo-gelatine plates of different makers in the saturated salt solution, and he thinks with perfect success. It takes 2-3 1/2 hours to clear the film; addition of liquid ammonia hastens the process. Albumen paper prints lose their chloride in the bath, but the silver albumenate remains and deepens in colour by light. The collodion prints show no sign of alteration in light up to the present time.
Collodio-chloride paper is much made in Germany, the best known makers being Obernether of Munich, and Linde of Lubeck. A quire of this paper costs, including carriage and packing, something like 21. 10s.; but as there are now and again streaky sheets in the parcels, that will not produce good prints, the above sum scarcely covers the price really paid. The size of the sheets is 22 by 17 in., which gives 30 C.D.V. pieces, or 10 cabinets. More might be cut from the sheet, but as the edges sometimes fray in the toning and washing, it is better to leave a sufficient margin, so that when trimming the prints a clean and firm edge may be secured. The paper will keep good in a cool place for 2-3 months. The printing should not be so deep as when using albumenised paper, as collodio-chloride prints lose very little of their vigour in passing through the toning and fixing baths. Collodio-chloride prints may be kept for a considerable time before toning - 2-3 weeks may elapse - but many prefer toning as soon after printing as possible.
The toning bath is made as follows: -
Stock Solution (a).
Ammonium sulphocyanide 1 oz. 2 dr. Distilled water .. .. 60 oz. Soda hyposulphite .. .. 9 gr.
Stock Solution (6). Pure gold ...... 11 er. or Gold chloride...... 22 gr. Distilled water .. .. 60 gr.
Fixing Bath, Soda hyposulphite .. .. 1 oz. Distilled water .. .. 12 oz.
The gold used for toning is prepared according to Col. Stuart Wortley's formula; it gives mote uniform results when toning collodio-chloride paper than the ordinary commercial samples of gold chloride. The strength of the toning bath is thus more under control, which is absolutely necessary to success with collodio-chloride paper, as anything more than the strength given in the formula produces a flat eaten-out picture without any depth; while, on the other hand, too weak a toning bath gives heavy opaque brown tones. Thus, if the toning goes on too quickly, you lose depth and richness; if very slowly, a brown leathery tone is produced, which is far from satisfactory.
The reason in the first case is that the prints pass so rapidly from brown to black, that before you can well get them removed from the bath, the point where richness lies is often lost. And in the second place, the ammonium sulphocyanide solution in some measure destroys the transparency and purity of the prints when they are left too long in contact with it. Particular care and attention must therefore be given to the toning bath, so as to have it neither more nor less than the strength stated, as collodio-chloride photographs are much easier stained in toning than prints upon albumenised paper; and when unequal toning does take place, it is more visible in the former than in the latter.