PHOTOGRAPHIC NOTES AND QUERIES.
Photographic Gun-Cotton.—The "doctors differ" not a little in their prescriptions for preparing the best gun-cotton for photographic use. How shall the photographer decide between them?
Dr. Diamond ("N. & Q.," Vol. vi., p. 277.) says (I quote briefly), "Pour upon 100 grains of cotton an ounce and a half of nitric acid, previously mixed with one ounce of strong sulphuric acid. Knead it with glass rods during five minutes," &c.
Mr. Hunt, quoting, (apparently with approbation) from Mr. Archer, says (p. 260., 3rd edit.), "Take one ounce by measure of nitric acid, mixed with one ounce by measure of ordinary sulphuric acid, and add to them eighty grains of cotton; well stir," &c., "for not more than FIFTEEN SECONDS," &c. "It will be seen that the cotton is not exposed to the action of the mixed acids in this last mode longer than is necessary to saturate the cotton; should the action be continued further, the solubility of the cotton is entirely lost."
Not only is the order of manipulation different (a point probably not material), but the time between "five minutes" and "fifteen seconds" must exercise a most important influence on the result. Who is right?
Cokely.
Sealing-wax for Baths.—I notice in your answers to correspondents (No. 176., p. 274.), that you inform H. Henderson that glass may be cemented for baths with sealing-wax. May I recommend to H. Henderson the use of gutta percha, instead of glass, for that purpose? Sheet gutta percha is now very cheap, and the baths are most easily made. I have had one of my own making in constant use since last July, having never emptied it but twice, to filter the nitrate of silver solution. It is not liable to breakage. The joinings are much less liable to leakage. And when it is necessary to heat slightly the silver solution (as it has been during the late cold weather), I have adopted the following simple plan: Heat moderately a stout piece of plate glass; plunge it into the bath; repeat the operation according to the size of bath. It is very useful to make a gutta percha cap to cover over the bath when not in use; it protects it from dust and evaporation, and saves the continual loss of materials arising from pouring the solution backwards and forwards. For home-work I have reduced
the whole operation to a very simple system. My bath, hypo-soda, developing fluid (of which, as it keeps so long, I make ten ounces at a time), are always ready in a small closet in my study. These I arrange on my study-table: a gutta percha tray, a brass levelling-stand upon it, a jug of soft water, and half-a-dozen small plates to place my pictures on, after treating them with the hypo-solution (for, to save time, I do not finish washing them until I have done all the pictures I require). All these things I can prepare and arrange in less than ten minutes, and can as easily return them to their places afterwards.
With regard to Mr. Mabley's process, described in "N. & Q.," No. 176., p. 267., as I am but a beginner myself, and have much to learn, I should be sorry to condemn it; but I should fear that his pictures would not exhibit sufficient contrast in the tints. Nor do I see the advantage the pictures would possess, if they did, over positives taken by our process. We amateurs in the country labour at present under great disadvantages, some of which I think the Photographic Society will remove. I am myself quite unable to form an idea what the collodion pictures done by first-rate photographers are like. All the positives done by amateurs in this part of the world, and developed by pyrogallic acid, which I have seen, present a dirty brown hue, by no means pleasing or artistic; and I have seen but very few, either developed by pyrogallic acid or protosulphate of iron, free from blemishes. I think if we were to act upon the suggestion made in "N. & Q." some time back, and send the editor a specimen of our performances, it would be a slight return for his endeavours in our behalf; and he would, I doubt not, honestly tell us whether our pictures were tolerable or not. I, for one, shall be very happy to do so.
J. L. Sisson.
Edingthorpe Rectory.
Developing Chamber.—I think Mr. Sisson will find some difficulty in applying his very excellent idea of a sheet India rubber lighting medium to his portable laboratory, as the vapour of the ether will act upon it and render it sticky and useless after one or two usings. Allow me to suggest what I am in the habit of using, viz. a double layer of yellow glazed calico, stuck together with a little common drying oil, and allowed to dry for a few days: this causes a perfect exclusion of the actinic rays, and is very durable.
F. Maxwell Lyte.
Falkland, Torquay.
The Black Tints on Photographic Positives.—A correspondent having inquired how these were obtained, and another replying that it was caused by starch, I beg to offer a process to your readers as to how they may obtain those carbonic tints; though I must premise that the process requires some skill, and is not always successful, though always sure to make them black: but on occasions of failure the lights sink, and the brilliancy of the picture is lost. That it is not starch in the French process, unless that vehicle contains some preparation, I am tolerably certain; the chloride of barium will often produce black images, though very uncertain; and the black process as given by Le Gray is uncertain also. For myself, I generally prefer the colour given by ammoniac salt; it is artistical and sufficient for any purpose. The present process, which I use myself when I require a black colour, with its imperfections, I offer to the photographic readers of "N. & Q.," and here it is.
Take a two-ounce vial, and have some powdered litharge of lead, by some called gold or scale litharge; pound it fine in a Wedgewood mortar, and put in the vial about one scruple; pour on it about half an ounce of Beaufoy's acetic acid, but do not replace the cork or stopper, as the gas evolved is very active, and will burst the vial, placing the operator's eyes in jeopardy; agitate and allow it to stand some hours to settle, or leave it till next day, when it will be better for the purpose: then decant the clear part and throw the fæces away, return the solution into the bottle, and fill up with distilled water. The positive paper being now prepared with the ammonio-nitrate of silver, and placed as usual in the sun, the artist must remove it when a tolerably distinct image is visible, but not altogether up: this is one of the niceties of the process; if it is too much done the blacks will be too black, and if not enough they will be feeble and want richness; it is when a visible image of the whole is developed: at this point put the positive into cold water; this will remove a great deal of the silver that has not been acted upon by the light: let it soak three or four minutes; take it out and blot off the water, laying a clean piece of paper below. Now pour a small quantity of the solution of lead on one end, and with a glass rod pass it carefully over every part; blot it off, and giving the paper a little time to dry partially, pass over a solution of newly made gallic acid; the shadows will rapidly become perfectly blank, and the picture will come up. But another nicety in the process is the point at which it must be plunged into hyposulphite of soda solution; if plunged in too soon the black will be mingled with the sepia tints, and if too late the whole tint will be too black. I offer it, however, because I know its capabilities of improvement, and the intensity of the black is sometimes beautiful: it is better suited for architectural subjects, where there is but little sky, as it will lay a faint tint over it; but if a sky is attempted, it must be kept under by a brush with a little hyposulphite of soda solution, touching it
carefully. The time it will take in becoming black will not exceed one minute; but as the eyesight is the guide, the moment the tints have changed from red to black is the proper time to arrest its further progress: the combination thus obtained will not change, nor, I believe, become faint by time; but I repeat it may be much improved, and if any abler hand, or one with better means at his disposal, will take the trouble to examine its capabilities, I shall be very thankful for his notes on the subject.
N.B. The solution of lead must contain acid; and if by keeping it does not change litmus-paper, acid must be added till it does.
Weld Taylor.
7. Conduit Street West.