C. B. (Birmingham). If the hyposulphite of soda is not thoroughly removed from a Photograph, it will soon become covered with reddish spots, and in a short time the whole picture may disappear. If cyanide of potassium has been used, it is requisite that the greatest care should be used to effect its removal entirely.
W. L. (Liverpool). A meniscus lens of the diameter of four inches should have a focal length of twenty inches, and will produce perfect landscape pictures fourteen inches square. It is said they will cover fifteen inches; but fourteen they do with great definition. We strongly advise W. L. to purchase a good article. It is a bad economy not to go to a first-rate maker at once.
J. M. S. (Manchester). You will find, for a screen to use in the open air, that the white cotton you refer to will be far too light. "Linsey woolsey" forms an admirable screen, and by being left loose upon a stretcher it may be looped up so as to form drapery, &c. If you cannot depend upon the collodion you purchase in your city, pray use your ingenuity, and make some according to the formulary given in Vol. vi., p. 277., and you will be rewarded for your trouble.
C. E. F. The various applications to your bath which you have used have destroyed it in all probability past use. All solutions containing silver will precipitate it in the form of a white powder, upon the addition of common salt; and from this chloride the pure metal is again readily obtained. The collodion of some makers always acts in the manner you describe; and we have known it remedied by the addition of about one drachm of spirits of wine to the ounce of collodion. Spirits of wine also added to the nitrate bath—two drachms of spirits of wine to six ounces of the aqueous solution—is sometimes very beneficial. When collodion is inert, and the colour remains a pale milk and water blue after the immersion, a few drops of saturated solution of iodide of silver may be added, as it indicates a deficiency of the iodide. Should the collodion then be turbid, a small lump of iodide of potassium may be dropped into the bottle, which by agitation will soon effect a clearance; when this is done, the fluid may be poured off from the excess of iodide which remains undissolved.
Alex. Rae (Banff). You shall have a private reply at our earliest leisure. The questions you ask would almost comprise a Treatise on Photography.
H. N. (March 30th). 1st. You will find the opacity you complain of completely removed by the use of the amber varnish, as recommended by Dr. Diamond, unless it proceeds from light having acted generally upon your sensitive collodion in the bath, or during the time of its exposure in the camera; in which case there is no cure for it.—2ndly. A greater intensity in negatives will be produced without the nitric acid, but with an addition of more acetic acid the picture is more brown and never so agreeable as a positive. 3rd. The protonitrate of iron used pure produces a picture as delicate, and having all the brilliancy of a Daguerreotype, without its unpleasant metallic reflexion—the fine metal being deposited of a dead white; and combined with the pyrogallic acid solution in the proportion of one part to six or ten, produces pictures of a most agreeable ivory-like colour.—4th. The protonitrate of iron, when mixed with the pyrogallic acid solution, becomes of a fine violet blue; but after some minutes it darkens. It should only be mixed immediately before using. The colour of the protonitrate of iron will vary, even using the same chemicals. The cheap nitrate of barytes of commerce answers exceedingly well in most cases; but a finer silver surface is obtained by the use of the purified.—5th. We have generally succeeded in obtaining portraits in an ordinary room, the sitter being placed opposite and near the window: of course, a glass-house is much better, the roof of which should be of violet glass, ground on the inner side. This glass can be bought, made especially for the purpose, at 11d. the square foot. It obstructs no chemical rays of light, and is most pleasant to the eyes, causing no fatigue from the great body of light admitted.
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