PHOTOGRAPHIC NOTES AND QUERIES.
Mr. Weld Taylor's Process.—As I presume the object of publishing Photographic Notes, &c., is to aid those who are not proficients in the processes indicated, Mr. Weld Taylor must not take umbrage at his first communication being misunderstood, whether unavoidably or wilfully, as I am sure the former must have been the case with all novices in the photographic art at least; however, I had no intention whatever of offering any annoyance to Mr. Taylor in my remarks, which were intended solely with a view to produce an effect which has partially been successful, that of exciting a more definite explanation of his meaning. That Mr. Weld Taylor may "enlighten" me is not only possible, but very probable, and I can only say I shall be much obliged to him for so doing.
With reference to his process for iodizing Canson's paper, I presume his meaning to be as follows, viz.: Mix half an ounce of a forty-grain solution of nitrate of silver with an equal quantity
of a fifty-grain solution of iodide of potassium, by which a precipitate of iodide of silver will be formed, the supernatant fluid containing the excess of iodide of potassium and the nitrate of potash formed by the decomposition. Add drop by drop a solution of the cyanide of potassium, until the iodide of silver is redissolved, and the liquid becomes limpid, and then four ounces more of distilled water, making up five ounces altogether. The paper should then be washed over with the above and dried, after which it may be floated on water slightly acidulated with sulphuric acid for a few minutes, and after being again dried, either wholly, or else partially with blotting-paper, may be rendered sensitive with a weak solution of nitrate of silver. Here are two or three points admitting doubt: first, Would it not be better to wash away the nitrate of potash and free iodide of potash first, and then dissolve the iodide of silver in solution of cyanide of potassium? Secondly, Would not a slight soaking in plain water after the acidulated bath be of advantage? Thirdly, Is it better to dry the paper again before rendering it sensitive? and fourthly, What strength of nitrate of silver solution should be used to render it sensitive; and ought it to have any acetic or gallic acid, or both?
George Shadbolt.
Animal Charcoal in Photography.—Perhaps you or one of your photographic correspondents would inform me whether the animal charcoal, recommended for the aceto-nitrate of silver solution, should be used as a filter, or simply allowed to remain in the bottom of the bottle?
A. B. C.
Oxford.
Sir W. Newton on Use of Common Soda and Alum.—In reply to W. Adrian Delferier, who is desirous of knowing the "rationale of the action of the common soda and powdered alum, &c.," my motive for using common soda to cleanse the negatives is, that it not only removes the hyposulphite of soda more readily, but any impurities which may be in the paper, as well as the whole of the size, such being absolutely necessary for the after waxing process; which, when done, the negative should appear nearly as transparent as glass.
The reason why I prefer alum for the positives is, that while it has the effect of removing the hyposulphite of soda and other impurities in the paper, it does not act upon the size, which in this instance it is desirous to retain.
I have been induced to make a series of experiments, with a view to prevent the fading of the positives, or, indeed, that any portion should be, as it were, eaten away in parts; and since I have adopted the foregoing, in no one instance has any change taken place whatever.
W. J. Newton.
6. Argyle Street.
Difficulties in Photographic Practice.—Having met with some of the difficulties that your correspondent G. H. mentions in his communication (Vol. vii., p. 218.), I beg to offer a few hints which I think will be of service to those who are trying the waxed-paper process.
With regard to the spots, it is not easy to know whether they are produced by particles of iron in the paper, or by the oxide of silver. Le Gray says: "If spots should form, produced by the oxide of silver, they may be removed by pouring over the negative some acetic acid, and passing a brush lightly over it."
The second difficulty, want of depth of tone or intensity in the negative, may have been caused by too short an exposure in the camera, or not having used the proper proportion of developing solution. Try the following:
4 oz. dist. water.
8 grains gallic acid.
When this solution has been filtered, add to it ½ drachm of the aceto-nitr. of silver solution, and 1 drachm of acetic acid. I have generally put a little camphor in the gallic acid solution, as recommended by Laborde. It prevents the decomposition of the gallic acid, and renders the image clearer and free from spots. A piece about the size of a pea for four or five ounces of solution.
As to the third difficulty, I believe nothing but replacing the porcelain dishes by glass ones will prevent the dirty marbled appearance in the bottom of the dishes made of porcelain; they are generally rough and uneven on the surface, and there are often what is called "kiln-cracks" in the angular parts. Two months ago I bought two glass dishes; although they are more than double the price of porcelain, I expect the annoyance of dirty dishes is prevented. The glass ones are made quite round at the sides and ends, and of course will be easily cleaned. I am informed they are made in France, but they could be had of English manufacture.
The animal charcoal in the sensitive solution must be shaken up in the aceto-nitrate solution; and when it has become quite clear, the solution before using must be filtered into the dish.
R. Elliott.
Penslur Iron Works.