PHOTOGRAPHIC CORRESPONDENCE.
Improvements in the Albumenized Process.—Your expectation of being soon able to announce the successful manufacture of a new negative calotype paper, will, I am sure, be gladly received by many photographers, and especially by those who, like me, have been subjected to much disappointment with Turner's paper. For one sheet that has turned out well, at least half-a-dozen have proved useless from spottiness, and some sheets do not take the iodizing solution evenly, from an apparent want of uniformity in the texture of the paper, which causes the solution to penetrate portions the moment it is laid on the solution. Undoubtedly, when it does succeed, it is superior to Whatman's, but this is not enough to compensate for its extreme uncertainty.
In Dr. Diamond's directions for the calotype, he gave a formula for the addition of bromide of potassium to the iodide of potassium, but did not speak with much certainty as to the proportions. Will he kindly say whether he has made farther trials; and if so, whether they confirm the proportions given by him, or have led him to adopt any change in this respect? and will he likewise say whether the iodizing solution which he recommends for Turner's paper, is suitable also to Whatman's?
In albumenizing paper, I have not found it desirable to remove the paper very slowly from the solution. Whenever I have done so, it has invariably dried with waves and streaks, which quite spoiled the sheet. A steady motion, neither too slow nor too quick, I have found succeed perfectly, so that I now never spoil a sheet. I have used the solution with less albumen than recommended by Dr. Diamond. My formula has been.—
Albumen 8 oz.
Water 12 oz.
Muriate ammon. 60 grs.
Common salt 60 grs.
And this, I find, gives a sufficient gloss to the paper; but that of course is a matter of taste.
I have not either found it essential to allow the paper to remain on the solution three minutes or longer, as recommended by Dr. Diamond. With Canson paper, either negative or positive, a minute and a half has been sufficient. I have used two dishes, and as soon as a sheet was removed, drained, and replaced, I have taken the sheet from the other dish. In this way I found that each sheet lay on the solution about one and a half minutes, and with the assistance of a person to hang and dry them (which I have done before a fire), I have prepared from forty to forty-five sheets in an hour, requiring of course to be ironed afterwards.
I have tried a solution of nitrate of silver of thirty grains to one ounce of distilled water, to excite this paper, and it appears to answer just as well as forty grains. I send you two small collodion views, takes by me and printed on albumenized paper prepared as mentioned, and excited with a 30-grain solution of nitrate of silver.
Is there any certain way of telling the right side of Canson paper, negative and positive? On the positive paper on one side, when held in a particular position towards the light, shaded bars may be observed; and on this side, when looked through, the name reads right. Is this the right or the wrong side?
C. E. F.
Since I wrote to you last, I have tried a solution of twelve grains only of nitrate of silver to the ounce of distilled water, for the paper albumenized, as mentioned in my letter of the 13th of February, and have found it to answer perfectly. The paper I used was thin Canson, floated for one minute exactly on the solution; but I have no doubt the thick Canson will succeed just as well; and here I may observe that I have never found any advantage in allowing the paper to rest on the solution for three or four minutes, as generally recommended, but the contrary, as the paper, without being in the least more sensitive, becomes much sooner discoloured by keeping. My practice has been to float the thin Canson about half a minute, and the thick Canson not more than a minute.
C. E. F.
Mr. Crookes on restoring old Collodion.—I am happy to explain to your correspondent what I consider to be the rationale of the process.
The colour which iodized collodion assumes on keeping, I consider to be entirely due to the gradual separation of iodine from the iodide of potassium or ammonium originally introduced. There are several ways in which this may take place; if the cotton on paper contain the slightest trace of nitric acid, owing to its not being thoroughly washed (and this is not as easy as is generally supposed), the liberation of iodine in the collodion is certain to take place a short time after its being made.
It is possible also that there may be a gradual decomposition of the zyloidin itself, and consequent liberation of the iodide by this means, with formation of nitrate of potassa or ammonia; but the most probable cause I consider to be the following. The ether gradually absorbs oxygen from the atmosphere, being converted into acetic acid; this, by its superior affinities, reacts on the iodide present, converting it into acetate, with liberation of hydriodic acid; while this latter, under the influence of the atmospheric oxygen, is very rapidly converted into water and iodine.
I am satisfied by experiment that this is one of the causes of the separation of iodine, and I think it is the only one, for the following reason; neither bromised nor chlorised collodion undergo the slightest change of colour, however long they may be kept. Now, if the former agencies were at work, there is no reason why bromine should not be liberated from a bromide as well as iodine from an iodide; but on the latter
supposition, could take place, the affinities of acetic acid being insufficient to displace hydrobromic acid.
A great many experiments which I tried last autumn, for the express purpose of clearing up this point, have convinced me that, cæteris paribus, the addition of free iodine to the iodizing solution, tends to diminish the sensitiveness of the subsequently formed iodide of silver. On paper, this diminution of sensitiveness is attended with some advantages, so that at present I hardly know whether to introduce the free iodine or not; but in collodion, as far as my experience goes, I see no reason for retaining it; on the contrary, everything seems to be in favour of its removal.
I can hardly imagine that the increased sensitiveness mentioned by Mr. Hennah is really due to the free iodine which he introduces. Such a result being so contrary to all my experience, I would venture to suggest that there must be some other cause for its beneficial action; for instance, commercial iodide of potassium is generally alkaline, owing to impurities present; the tincture of iodine in this case would render the collodion neutral, and unless a very large excess of iodine were introduced, its good effects would be very apparent. This, however, involving the employment of impure chemicals, is a very improbable explanation of a phenomenon observed by so excellent an operator as Mr. Hennah: there is most likely some local cause which would be overlooked unless expressly searched for.
With regard to the point, whether the free iodine is the sole cause of the deterioration of old collodion, I should say decidedly not, at least in a theoretical view; the liberation of free iodine necessitates some other changes in the collodion, and the result must be influenced by these in one way or another, but practically I have as yet found nothing to warrant the supposition that they perceptibly interfere with the sensitiveness of the film.
In the above I have endeavoured as much as possible to avoid technicalities, in order to make it intelligible to amateurs; but if there be any part which may be considered obscure, on its being pointed out to me, I will endeavour to solve the difficulty.
William Crookes.
Hammersmith.
Photographic Queries.—1. Would you, Sir, or Dr. Diamond (Dr. Mansell is too far off), be kind enough to inform your readers whether Dr. Mansell's process, recommended in No. 225., is equally applicable to inland as to sea-side operations; or must we, in the one case, follow Dr. Diamond, and in the other Dr. Mansell, and thus be compelled to prepare two sets of papers?
2. Dr. Mansell recommends, as a test for the iodized paper, a strong solution of bichloride of mercury; may we ask how strong?
3. Mr. Sisson's developing fluid has undergone so many changes, and has been so much written about, that we are at a loss to discover or to determine whether it has been at length settled, in the mind of the inventor, that it will do equally well for negatives as for positives.
Four Photographic Readers.
[1. Both papers are equally available for both purposes. In actual practice we have not ourselves experienced any difference in their results.
2. It is quite immaterial. A drachm of bichloride dissolved in one ounce of spirits of wine will cause a cloudiness and a precipitate, if a very few drops are added to the tested water.
3. In general the salts of iron are more adapted for positives, and weak pyrogallic acid solutions for negatives; say one and a half grain of pyrogallic acid, twenty minims of glacial acetic acid, and an ounce of distilled water.]