PHOTOGRAPHIC CORRESPONDENCE.
Glass Chambers for Photography.—I am desirous to construct a small glass chamber for taking portraits in, and shall be much obliged if you can assist me by giving me instructions how it should be constructed, or by directing me where I shall find clear and sufficient directions, as to dimensions, materials, and arrangements. Is it essential that it should be all of violet-coloured glass, ground at one side, as that would add a good deal to the expense? or will white glass, with thin blue gauze curtains or blinds, answer?
Probably a full answer to this inquiry, accompanied with such woodcut illustrations as would be necessary to render the description complete, and such as an artificer could work by, would confer a boon on many amateur photographers, as well as your obliged servant,
C. E. F.
[In the construction of a photographic house, we beg to inform our correspondent that it is by no means needful to use entirely violet-coloured glass, but the roof thereof exposed to the rays of the sun should be so protected; for although the light is much subdued, and the glare so painful to the eyes of the sitter is taken away, yet but few of the actinic rays are obstructed. It has been proposed to coat the interior with smalt mixed with starch, and afterwards varnished; but this does not appear to have answered. Calico, both white and coloured, has also been used, but it is certainly not so effectual or pleasant. Upon the whole, we think that the main things to attend to are, firmness in its construction, so as to avoid vibration; ample size, so as to allow not only of room for the operator, but also for the arrangements of background, &c., and the sides to open so as to allow a free circulation of air; blinds to be applied at such spots only as shall be found requisite. Adjoining, or in one corner, a small closet should be provided, admitting only yellow light, which may be effectually accomplished by means of yellow calico. A free supply of water is indispensable, which may be conveyed both to and from by means of the gutta percha tubing now in such general use. We apprehend, however, that the old proverb, "You must cut your coat according to your cloth," is most especially applicable to our querist, for not only must the house be constructed according to the advantages afforded by the locality, but the amount of expense will be very differently thought of by different persons: one will be content with any moderate arrangement which will answer the purpose, where another will be scarcely satisfied unless everything is quite of an orné character.]
Dr. Diamond's Replies.—I am sorry I have not before replied to the Queries of your correspondent W. F. E., contained in Vol. viii., p. 41.; but absence from home, together with a pressure of public duties here, has prevented me from so doing.
1st. No doubt a small portion of nitrate of potash is formed when the iodized collodion is immersed in the bath of nitrate of silver, by mutual decomposition; but it is in so small a quantity as not to deteriorate the bath.
2nd. I believe collodion will keep good much longer than is generally supposed; at the beginning of last month I obtained a tolerably good portrait of Mr. Pollock from some remains in a small bottle brought to me by Mr. Archer in September 1850; and I especially notice this fact, as it is connected with the first introduction of the use of collodion in England. Generally speaking, I do not find that it deteriorates in two or three months; the addition of a few drops of the iodizing solution will generally restore it, unless it has become rotten: this, I think, is the case when the gun cotton has not been perfectly freed from the acid. The redness which collodion assumes by age, may also be discharged by the addition of a few drops of liquor ammoniæ, but I do not think it in any way accelerates its activity of action.
3rd. "Washed ether," or, as it is sometimes called, "inhaling ether," has been deprived of the alcohol which the common ether contains, and it will not dissolve the gun cotton unless the alcohol is restored to it. I would here observe that an excess of alcohol (spirits of wine) thickens the collodion, and gives it a mucilaginous appearance, rendering it much more difficult to use by its slowness in flowing over the glass plate, as well as producing a less even surface than when nearly all ether is used. A collodion, however, with thirty-five per cent. of spirits of wine, is very quick, allowing from its less tenacious quality a more rapid action of the nitrate of silver bath.
4th. Cyanide of potassium has been used to re-dissolve the iodide of silver, but the results are by no means so satisfactory; the cost of pure iodide of potassium bought at a proper market is certainly very inconsiderable compared to the disappointment resulting from a false economy.
H. W. Diamond.
Surrey County Asylum.
Trial of Lenses.—When you want to try a lens, first be sure that the slides of your camera are correctly constructed, which is easily done. Place at any distance you please a sheet of paper printed in small type; focus this on your ground glass with the assistance of a magnifying-glass; now take the slide which carries your plate of glass, and if you have not a piece of ground glass at hand, insert a plate which you would otherwise excite in the bath after the application of collodion, but now dull it by touching it with putty. Observe whether you get an equally clear and well-focussed picture on this; if you do, you may conclude there is no fault in the construction of your camera.
Having ascertained this, take a chess-board, and place the pieces on the row of squares which run
from corner to corner; focus the middle one, whether it be king, queen, or knight, and take a picture; you will soon see whether the one best in the visual focus is the best on the picture, or whether the piece one or more squares in advance or behind it is clearer than the one you had previously in focus. The chess-board must be set square with the camera, so that each piece is farther off by one square. To vary the experiment, you may if you please stick a piece of printed paper on each piece, which a little gum or common bees'-wax will effect for you.
In taking portraits, if you are not an adept in obtaining a focus, cut a slip of newspaper about four inches long, and one and a half wide, and turn up one end so as it may be held between the lips, taking care that the rest be presented quite flat to the camera; with the help of a magnifying-glass set a correct focus to this, and afterwards draw in the tube carrying the lenses about one-sixteenth of a turn of the screw of the rackwork. This will give a medium focus to the head: observe, as the length of focus in different lenses varies, the distance the tube is moved must be learned by practice.
W. M. F.
Is it dangerous to use the Ammonio-Nitrate of Silver?—Some time ago I made a few ounces of a solution of ammonio-nitrate of silver for printing positives; this I have kept in a yellow coloured glass bottle with a ground stopper.
I have, however, been much alarmed, and refrained from using it or taking out the stopper, lest danger should arise, in consequence of reading in Mr. Delamotte's Practice of Photography, p. 95. (vide "Ammonia Solution"):
"If any of the ammonio-nitrate dries round the stopper of the bottle in which it is kept, the least friction will cause it to explode violently; it is therefore better to keep none prepared."
As in pouring this solution out and back into the bottle, of course the solution will dry around the stopper, and, if this account is correct, may momentarily lead to danger and accident, I will feel obliged by being informed by some of your learned correspondents whether any such danger exists.
Hugh Henderson.