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410 THE PHOTOGRAPHIC NEWS. [August- 29,1862. On the use of thia collodion in the operating room, ho adds :—• “ The same bromo-iodized collodion, with the nitric acid bath, was also tried for portraiture, and found to effect a considerable saving in the time of exposure; but the use of the two deve lopers, and the long time occupied in the development, is some what against it. Where, however, a short sitting is desired, the extra trouble must be put up with ; against this must be placed the ease and cleanliness of working with a collodion con taining bromide.” As to the value of a bromide in securing immunity from spots, &c., we have testimony even in that part of the book which is devoted solely to the use of iodized collodion ; and we are glad to find our own experience as to the marked effect of a very infinitesimal dose in this respect, in reference to which our friend Sutton has charged us with over refine ment. Referring to transparent spots being common when using newly iodized collodion, Mr. Ponting recommends the addition to each ounce of from five to ten drops of a 20- grain solution of bromide of ammonium in spirits of wine. Twelve drops or minims of this solution would contain just half a grain of bromide, so that the addition recommended is from a quarter of a grain to half a grain of bromide per ounce. This, it must be borne in mind, is to be added to the collodion sold ready iodized, if used new and producing spots. Mr. Ponting’s book will be read with great interest by all photographers. He. divides his work into six parts. These treat of the Chemicals, of the Manipulations, of Failures—their Causes and Remedies, of Positive Pictures on Glass, of Printing, &c., and of Instantaneous Pictures. Perhaps, if any exception be taken to the work at all, it will be to its title, “ Photographic Difficulties.” It is really rather a useful manual of formulas and manipulations, than a treatise upon difficulties, which do not occupy a larger space than is customary in manuals. It is quite true, how ever, that if the photographer follow carefully the instruc tions given as to precision and care, he will not be likely to meet with many troubles, and in this sense the title may be regarded as no misnomer. TRANSPARENCIES ON GLASS. Wb have recently received from one of our amateur readers, Mr. Thomas Ratcliffe, of Colne, half a dozen very beautiful stereoscopic transparencies. They are characterized by un usually perfect and delicate definition, fine tone, and atmo spheric effect; some of them possessing natural clouds. The tones are chiefly of a purple black, and they are remarkably brilliant and clean. In a conversation with Mr. Ratcliffe we learnt that they were all from dry plate negatives, pro duced by the tannin process, or the resin process; and that the transparencies were on plates prepared in all respects as those on which were produced the negatives. They were all printed by superposition by gas light, and from the short ness of the exposure both in printing and in obtaining the negatives, it was evident that as dry plates they possess a considerable degree of sensitiveness. In reference to the printing by gas light, Mr. Ratcliffe referred to a common fallacy in the instructions for conduct ing the exposure : it is usually recommended if a simple gas flame bo used, without a reflector, that the frame holding the negative and sensitive plate should be moved about so as to secure equality of illumination all over the plate. This Mr. Ratcliffe strongly objects to, with very sufficient reason ; it is next to impossible, as he asserts, to bring the two rigid surfaces of glass, that of the negative and sensitive plate, into absolutely perfect contact; and such being the case, if the rays of light strike the surface of the negative obliquely, refraction ensues, with a consequent loss of sharpness in the positive. But if the frame be held quite still, near to a moderately large gas flame, the rays reaching the surface of a single stereoscopic picture are so nearly parallel, and impinge so nearly at right angles, that no loss of sharp ness is perceptible. Since Mr. Ratcliffe was in London, ne has been so good as to respond to our request that he would prepare, for the benefit of our readers, a brief statement of the formulas and method of manipulating, by which he obtained such excellent results, both in producing negatives and transparent positives. We shall now give his brief but practical description: it will be seen that the operations throughout are very simple, and that the method of using acetic acid in the first washing, dispenses with its use in the silver solution, and permits the use of a bath nearly neutral, and in good condition for wet plates, instead of preserving one for use with wet plates only. Mr. Ratcliffe writes: “ In accordance with the promise made you to forward particulars respecting the way in which I work out the tannin and also the resin process, I shall now endeavour to do so as briefly as possible. “ Tannin PROCESS. “ Preparing Hie Plates.—Clean and dry the plates as usual, affix to plate-holder, breathe on the surface, and while moist pour over a dilute solution of albumen made as follows:— Albumen ... 1 ounce Water ... 4 ounces. Froth well; then add 12 drops liquor ammonia. Put the solution aside in a cool place for twenty-four hours, then bottle for use. Filter through a small bit of sponge placed in the neck of the funnel, to take out the air-bubbles as you coat each plate ; dry rapidly before the fire, and store away the plates for use. “ Exciting the Plates.— 1 Coat with collodion (I use Maw son’s negative), and allow the film to set pretty well, then immerse in the silver bath, the strength of which is 35 to 40 grains to the ounce, very slightly acid with nitric acid. Allow the plate to remain until arrangements are making for coating another, then remove without draining, into a small dish or tray containing— Water ... 6 to 8 ounces Glacial acetic acid ... ... 20 minims. Proceed to coat and prepare plate No. 2 ; when the latter is properly sensitized remove plate No. 1 to another dish con taining spring water,'placing No. 2 in the acetic bath. Wash well, place on levelling stand, and coat with tannin solu tion, made 15 grains to the ounce of water, filtered prior to use; let this remain on the plate until you coat and prepar 6 another plate, then stand on one corner to drain and dr)' spontaneously ; when thoroughly dry store away for use. “ Exposure.—With a fair light one minute will be sutti cient. “ Lens.—Portrait combination, 7-16th stop, 41 inch focal length. “ The Developer is made as follows :— Pyrogallic acid ... 2 grains Citric acid 2 „ Glacial acetic acid ... ... 2 drops Water ... ... ... ... 1 ounce. Moisten the surface of the spring water for one min and pour over about three drachms of developer, let this I main a few seconds, then add two drops of silver solution strength 20 grains to the ounce of water. This is sufficieni to bring out all the detail; if the developer becomes dis coloured, wash the plate and use a fresh supply, adding fl drops of silver, which in most cases is sufficient to'bring U P the required intensity. Fix with hypo as usual. If 4 deposit appears on the plate when dry, rub the surface wi a little cotton wool prior to varnishing.” 1:011 Mr. Ratcliffe is equally successful with resin plates, whte he finds a trifle more sensitive than the tannin. plate, or immerse in your tray o ite, place on the levelling stand. “ Resin Process. I “ Simply add to the collodion } grain of common rest
