ENGRAVING PHOTOGRAPHS UPON GLASS AND PORCELAIN. A process of engraving photog-raphs upon glass and porcelain was de scribed by Mr. Thomas Sims, at a meeting of the Photographic Society, on January 1st, 1857. The following is the account given by him of this process :— " Wishing to offer as much information as possible, without oc cupying too much space, I think I cannot do better than give the process of engraving photographs on glass, by means of hydro fluoric acid gas, in the form of notes, which have been penned at various times, generally after making the experiments. Previous to this, however, it is necessary to give a general idea as to the mode by which I have taken the kind of photograph most suitable for the pur pose. First, then, the collodion I use is thin ; it has as much alco hol as it will bear, adding ether only when it is too gelatinous, iodized with iodide of silver dissolved in an excess of iodide of po tassitun. The glass here is a desideratum, as it is not only necessary to obtain it free from strite and specks, but its component parts will, I believe, occupy the attention of photographers in time to come as much as paper has done for calotype. I have given crown, sheet, and several kinds of plate-glass very fair trials, and as yet I find none to yield so readily to the action of the hydro-fluoric acid gas as British patent plate.
" Some idea of the care I have taken to arrive at this conclusion may be perceived, when I state the manner in which I te.st,ed the quality. I have cut 9-inch plates of various kinds into four or six squares, putting each lot carefully apart ; I have then taken one of each kind and marked it ; collodionized and developed each with the same material, and photographed from the same model, such as a chalk bust or engraving, and have applied the hydro-fluoric acid in the same manner to each, and this two or three separate times, and in every case the patent plate showed itself to be most easily acted upon. Previous to putting on the collodion, and in order to cleanse the plate, I wash it in sulphuric acid and water.
" Bath.-30 grains of silver to the ounce of water, made in the usual way.
" The time in the camera is of consequence : it must be timed to a nicety, and developed well. (See Notes.) " The developing solution is made with different samples of proto sulphate of iron, pound of three or four samples, put together in rather a wide-mouthed bottle, and the crystals covered with distilled water, to which are added 2 drachms of acetic acid.
" When a developing solution, fit for use, is required, take 11 ounce of this saturated solution and put to it 6 ounces of distilled water and 2 drachms of acetic acid. If this does not flow evenly over,
add a drachm of alcohol ; but if it can be done without it is better, as the alcohol is liable to produce grey pictures.
" I invariably fix with hyposulphite of soda ; and too much care cannot be taken, to get out the iodide of silver (and the same may be said of the hyposulphite of soda), with abundance of water and wash or two with ammonia and water, and this, again, washed away with water.
" The plate must be dried with as much care as a daguerreotype and in the same manner, from the top downwards, evenly and regu larly : the water must not concentrate itself upon any particular part, so as to dry in patches ; for though the impression may pass through the burning process without showing the stain, it certainly will not stand the test of the hydrofluoric acid gas, for the stains themselves will be engraved.
" It will be found that if the most minute particle of the iodide or hypo remains in the impression after washing, it will turn black quickly while burning; and if heat be long applied the impression will evaporate altogether, and this at not a very high temperature. This is a fact that has so many times come under my notice, often to my sorrow, that I have been led to conclude, reasoning from analogy, that the hypo must be the great enemy to the durability of paper photographs; for if a collodion film, which we have so much more power over in the way of cleansing, will yet, after all the washing, retain sufficient quantity of hypo-sulphite to be the des truction of the photograph, how much more is paper likely to do so I "Burning the Photograph.—The only requisites necessary for this purpose are, boxes of sheet iron or tin of various sizes, and a stove, the top of which easily becomes slightly incandescent when the fire is lighted in it. The new boxes must be burnt to get rid of any grease-in the iron ones, and of the tin and grease in the tin ones. They must be made a quarter of an inch larger than the size of the plate to be burnt in them ; and they must also be rounded slightly at the bottom. If the first precaution be not taken, the box on cooling will contract and crack the glass. The reason for having the box a little rounded at the bottom is, to allow the operator to place the impression face downwards, which will enable him to stove the picture without having a cover on the box (provided the room be free from cold draughts), and to see how the process goes on ; this may be easily done by holding the box with pincers in such a posi tion as to get the reflected ray to the eye from the back of the im pression ; for, as the silver becomes reduced it assumes a mirror like appearance.