PHOTOGRAPHIC CORRESPONDENCE.
Mr. Sisson's developing Fluid.—Since I sent you the new formula for Mr. Sisson's positive developer, which you published in Vol. viii., p. 301., Mr. Sisson has written to me to say that if, instead of the acetic acid, you add two drachms of formic acid, the new agent proposed by Mr. Lyte, you certainly obtain the sweetest-toned positives he has ever seen. The pictures, he says, come out very quickly with it indeed; and with a small lens in a sitting-room he can in about ten seconds obtain the most wonderful detail. Every wrinkle in the face, and ladies' lace ribbons or cap-strings, he says, come out beautifully.
The formula then, as improved by Mr. Sisson, is—
Water 5 oz.
Protosulphate of iron 1½ drs.
Nitrate of lead 1 dr.
Formic acid 2 drs.
Perhaps you will give your readers the benefit of it in your next Number. Having tried it myself, I think they will be delighted with the beautiful white silvery tone, without any metallic reflection, produced in pictures developed with it.
J. Leachman.
20. Compton Terrace, Islington.
Dr. Diamond's Process for Albumenized Paper.—Photographers are under many obligations to Dr. Diamond, particularly for the valuable information communicated through "N. & Q.," and his obligingness in answering inquiries. I make no doubt he will readily reply to the following questions, suggested by his late letter on the process for printing on albumenized paper.
Will the solution of forty grains of common salt and forty grains of mur. amm., without the albumen, be found to answer for ordinary positive paper (say Canson's, Turner's, or Whatman's)? and, in that case, may it be applied with a brush?
Will the forty-grain solution of nit. sil. (without amm.) answer for paper so prepared? and may this also be applied with a brush?
Should the positives be printed out very strongly? and how long should they remain in the saturated bath of hypo.?
Is not the use of sel d'or subject to the objection that the pictures with which it is used are liable to fade in time?
Dr. Diamond says that pictures produced by the use of amm. nit. of silver are not to be depended on for permanency. If this be so, it is very important it should be known, as the use of amm. nit. is at present generally recommended and adopted.
C. E. F.
Mr. Lyte's New Process.—Although I presume it is none of your affair what is said or done in "another place," will you kindly ask Mr. Lyte for me, if he will be so good as to explain the discrepancy which appears between his "new processes," as given in the Journal of the Photographic Society of Sept. 21, and "N. & Q." of Sept. 10? In the former he says, for sensitizing, take (amongst other things) iodide of ammonia 60 grains: in "N. & Q.," on the contrary, what would seem to be the same receipt, or intended as the same, gives the quantity of this salt one fourth less, 45 grains—a vast difference. Again, in the developing solution the quantity of formic acid is double in your paper what it is in the journal.
I should not have trespassed on your space, but would have written to Mr. Lyte directly, except from the fear that some other unfortunate practitioner may have stumbled over the same impediment as I have done, and may not have had courage to make the inquiry.
S. B.
[Having forwarded this communication to Mr. Lyte, we have received from that gentleman the following explanations of his process, &c.]
The process which was published in the Photographic Journal was, I am sorry to say, not quite correct in its proportions, on account of a mistake in inclosing the wrong letter to the Editor; but the mistake will, I trust, be rectified by another communication which I have now sent.
The whole of the formulæ, however, as given in "N. & Q.," are quite correct.
Let me now, however, trespass on your pages by a few more answers to several other Querists, and which at the same time may be acceptable to some of your readers.
1. The developing agents which are made with iron are very applicable as baths to immerse the plate in; and the formic acid, from its powerful deoxidizing property, renders the iron salt more stable during long use and exposure to the air.
2. In coating paper with albumen, if the upper edge of the paper be sufficiently turned back, and the paper be forced down sufficiently on to the surface of the albumen, no bubbles will form; and
the operator will not be troubled with the streaks so often complained of.
3. No time can possibly be fixed for the exposure of the positive to the action of the hypo.; and to produce the best effects, the positive must be continually watched, both while printing and while in the hypo.
4. No hot iron should be applied to the positive after being printed, but the picture should be allowed to dry spontaneously.
5. The developing agent with the pyrogallic and formic acids will keep good a very long time, longer, I think, than that in which acetic acid is used, but cannot be used as a dipping bath.
6. I find the formic acid which I obtain from different chemists rather variable in its strength. What I use is rather below the average strength, so that in general about six drachms of the commercial acid will suffice where I use one ounce; but the excess seems to produce no bad result.
7. A great advantage of the pyrogallic developer which I recommend, is that of its being able to be diluted to almost any extent, with no other result than simply making the development slower. Another point is also worthy of notice, viz. a method by which even a very weak positive on glass may be converted into a very strong negative.
I take a saturated solution of bichloride of mercury in hydrochloric acid, and add of this one to six parts of water. This I pour over the collodion plate, and watch it till the whitening process is quite complete. Having well washed the surface with water, I pour over it a solution of iodide of potassium, very weak, not more than two or three grains to the ounce of water. The effect of this is to turn the white parts to a brilliant yellow, quite impervious to actinic rays. This process is only applicable to weak negative or instantaneous pictures, as, if used on a picture of much intensity, the opacity produced is too great. By using, however, instead of the iodide of potassium, a weak solution of ammonia, as recommended by Mr. Hunt, a less degree of intensity may be produced again a less intensity by hyposulphate of soda and a less degree again, but still a slight darkening, by pouring on the bichloride and pouring it off at once before the whitening commences. I thus can tell the exact degree of negative effect in any picture of whatever intensity. The terchloride of gold is most uncertain in its results, at any rate I find it so.
I must again beg you to excuse the great length of my communication, and hope it will be of service to my fellow photographers.
F. Maxwell Lyte.
Florian, Torquay.