The Photographic News. Vol. 10, No. 416. August 24, 1868. p.402

AN EXAMINATION
INTO THE CIRCUMSTANCES UNDER WHICH SILVER IS FOUND IN
THE WHITES OF ALBUMEN PRINTS

FUMED PAPER.

Fixed with Hyposulphite of Soda.

In the following trials the paper was sensitised upon a 40-grain acidulated bath, and was then fumed five minutes with ammonia.

(7) Lime toning.--Hydrosulphate of ammonia applied to the whites gave an indication slightly less than the average.

(5) Benzoate of gold toning.--About the same as the last.

(9) Citrate of gold toning.--About the same, or a little more indication of silver.

(10) A portion of the same print was toned in a bath prepared as follows :--Two ounces of hyposulphite of soda were dissolved in eight ounces of hot water, and chloride of gold corresponding to one grain metallic gold was added while hot. The bath was used two or three hours after mixing. This bath toned to a rich purple black. Marks made on the whites with hydrosulphate of ammonia could not be found after drying, thus indicating a complete absence of silver.

Sulphocyanide Fixing..

A print was made on paper sensitized on a 40-grain acidulated bath, fumed ten minutes with ammonia, and printed under a strong negative. It was then cut up.

(11) A portion was toned with alkaline chloride, and fixed with hyposulphite for a comparison. It gave, with sulphydrate of ammonia, results similar to those already noted.

(12) Toned in the same way, and fixed with sulphocyanide of potassium ^**--Result, with sulphydrate of ammonia, about the same as the foregoing.

(13) Toned and fixed in a bath of sulphocyanide of potassium and choloride of gold.--Result as before. A camel's-hair pencil dipped in dilute sulphydrate of ammonia, and drawn across the whites, leaves a well-marked pale buff streak.

(14) Toned and fixed in a bath of sulphocyanide of potassium and fulminating gold.--Result the same. (In fixing with sulphocyanide, it appears more difficult to keep the whites clean than with hyposulphite.)

Fixing and Toning Bath.

(15 and 16) Two further trials were made with the fixing and toning bath of hyposulphite and gold. In these the same bath as before was used, now four and five days old respectively. The results were the same. Whilst in every other case the marks produced by the sulphydrate were clear and well marked, in these last, as well as in (4) and (10), the marks were either invisible, or could only be found by close and attentive inspection. This result was to me altogether unexpected. The fixing and toning bath has been so loudly accused of all sorts of mischief, especially of being "wrong in principle" (which it certainly is not), that I was extremely surprised to find it possess this very striking superiority in so important a point.

I did not, however, rest contented even with these repeated trials. Having printed a number of prints from various negatives, I toned some of them in the ordinary methods, and fixed and toned some with the hyposulphite and gold. I then applied the sulphydrate to the high lights, and found that in all cases the same superiority existed. In fact, all the prints which had been so toned and fixed could be picked out by mere inspection of the sulphydrate mark.^***

I am, therefore, prepared to state, as a fact that does not admit of a doubt, that a print fixed and toned with hypo and gold contains less silver in the whites than when treated in any other of the methods which I have described. My remarks must be understood as applying to a bath properly managed. If the same bath is used until, by the action of the chloride of silver upon the hyposulphite, a quantity of tetrathionate of soda is formed, the results as respects the silver in the whites may be different. That is a point which I have not cared to examine; it would have no real value, whatever the result might be, as the use of such a decomposed bath is to be condemned on other grounds.

I am aware that the ground which I have taken here--namely, that a fixing and toning bath gives the purest whites, chemically speaking--will be apt to arouse much opposition. To such as may call my results in question, I say, prepare the bath as directed at (10), and observe the results. These are matters that must be judged by experience, not by theory. Nor is it to be supposed that I have been influenced in my conclusions by a prejudice in favour of this method. On the contrary, my prejudices were the other way. I had read such bitter attacks upon this mode of proceeding, that, except while making these experiments, I have never used it, but have toned and fixed separately.

I now come to another part of the same subject; a part in which I regret that I have not been able to arrive at any positive conclusions as satisfactory as I could wish. I think, however, my results will be worth stating briefly, both because I may save others the trouble of making similar investigations, and because, by illustrating the extraordinary tenacity with which the silver remains combined with the albumen, they give greater completeness to an examination which has required no small expenditure of time and attention.

The existence of silver in the highest lights, the purest whites of the finished picture, cannot be looked upon otherwise than as a very great evil. So long as it is there, there are far fewer chances for the permanence of the print; and if any way could be found for removing it, without injury to the rest of the picture, it would be a great advantage. This is a very difficult problem, and one which I have been as yet unable to solve. It was at one time asserted that fixing by sulphocyanide of ammonium removed this portion of the silver; but this again was contradicted and, as we have seen, very properly. Indeed, if there exists any preference in this respect, it is in favour of the hyposulphite. But the difference is too inconsiderable to be worthy of attention.

There is another important point to be borne in mind, which follows directly from the examinations here recorded, and which has not before been adverted to. As the silver in the whites is not there by any action of light, hut simply in combination with the albumen, this peculiar combination of silver and albumen is necessarily present in every part of the picture. It is not more present in the high lights than in the deep shadows, though its presence can only be made evident to the eyes in the former. The silver is present in an entirely different form from the reduced silver which constitutes the body of the picture until it is toned; it is liable to be differently affected by all external circumstances, and undoubtedly forms an element of weakness in the finished print.

The fact that silver is present, not by any influence of light, but simply in combination with the albumen, seemed to establish a possibility that some means might be found of dissolving it out, it seemed possible that some reagent could be found, which would either dissolve out this silver, or bring it into a condition of solubility in hyposulphite. Could such a reagent be found, it might either, according to its nature, be placed in the gold toning bath, if capable of such application without injury to the bath, or the prints might be passed through the solution immediately after their first washing. The following substances were examined

Ferrocyanide of potassium.
Ferridcyanide of potassium.
Iodide of potassium.
Bromide of potassium.
Chloride of ammonium.
Acetate of soda.
Phosphate of soda.

The papers, after being cleared of free nitrate of silver by washing, were placed in solutions of these respective substances for about ten minutes. They were then placed in a very strong solution of hyposulphite for a quarter of an hour, and then thoroughly washed. On testing them with sulphydrate of ammonia, together with a portion of the same prints treated in the ordinary way, on comparison no difference could be found, except that the paper treated with iodide of potassium gave a darker shade than any of the rest. In fact, iodide of silver dissolves in hyposulphite of soda much more slowly than chloride or bromide. A piece of paper prepared with iodide of silver retained its yellow colour almost unimpaired after fifteen minutes' exposure to a strong hypophosphite bath; some even remained at the end of half an hour. After eighty-five minutes the silver was perfectly gone, but sulphydrate of ammonia still produced the buff streak.

It follows, therefore, that no substance (as far as these experiments go), is capable of dissolving out the silver from the albumen.

^* Continued from p. 395.

^** The ammonium salt at the time when these trials were made was not to be had here. I therefore employed sulphocyanide of potassium of my own preparation and perfectly pure.

^*** Quite recently I have repeated these experiments with a similar result.