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THE PHOTOGRAPHIC NEWS. [June 29, 1883. to stop the process before we get emulsion which cannot be dried under ordinary conditions. We find that when we reach a point where dried plates give 229 or 23° Warnerke, we have reached the limit for ordinary circumstances. With conditions of weather, &c., very favourable, we have continued boiling farther, and have got a clear plate giving 25°. The next point for consideration is the amount of gela tine to be added ultimately to our emulsion. When an emulsion of the “ delicacy ”—if we may be allowed the term—which we have described is obtained, it will be readily understood that the more quickly drying can be performed, the less likely is fog to make its appear ance. On the other hand, we have found that the addition of a considerable quantity of gelatine has such a protecting influence on the particles of silver bromide, that it more than compensates for the longer time of drying which the extra thickness of film involves. In other words, a more sensitive emulsion may in practice be used if it contains a large proportion of gelatine than could be if the proportion were small. We find it of advantage to add to the emulsion, after boiling, a quantity of gelatine equal by weight to twice the silver nitrate which was used at first. PRODUCTION OF THE PHOTOGRAPHIC IMAGE ON THE WOOD BLOCK OF THE ENGRAVER. Before the wood engraver actually commences his work on the boxwood block, the subject matter is drawn by an artist, and, in all ordinary cases, the judgment of the engraver determines the exact method in which the original shadings shall be translated into line or stipple. It is many years ago since the first efforts were made to press photography into service as a means of producing guide pictures on the wood block; but most of the proposed methods failed to come into general use because the block was either spoiled by the action of fluids, or covered with a film calculated to interfere with the work of the engraver. One of the earlier methods, however—that of Mr. W. Crookes—was subject to neither of these objections; but, unfortunately, the surface remained sensitive, so that the cutting operations had to be performed by a feebly actinic light. Mr. Crookes merely rubbed the surface of the block with oxalate of silver, and printed on this directly from the negative. We have repeatedly pointed out in the Photographic News that the only kind of photographic image which is entirely satisfactory from a wood engraver’s point of view is a fatty image, somewhat of the nature of a photo-litho graphic transfer, and we now propose to give simple and easy directions by which any photographer may readily make such a transfer for himself and put it down on the wood block. A planished zinc or copper plate is slightly roughened by means of No. 2 emery cloth, and mounted on a levelling stand in a warm place ; the hob of an ordinary kitchen fire-place answers very well indeed, but it is neces sary to place a screen so as to protect the plate from falling particles. When a thermometer placed a couple of inches over the plate indicates a temperature of 100° to 110° F., all is ready for pouring on the gelatine solution, which is made as follows: — Coignet’s “ gold label ” gelatine 1} drachms Water ounces Dissolve in a water bath, and stir in powdered ammonium bichromate 10 grains. The solution should be strained through muslin, poured on the plate, and spread uniformly by means of a strip of paper ; this quantity of sensitive mixture being about that required for a 6 by 8 plate. If the temperature rises too high, there will be a risk of the gelatine scaling off at the edges, or blistering up during the subsequent operations. When dry, the plate is exposed under a reversed negative, the exposure being a trifle less than that required for pro ducing an ordinary silver print; and the exposure being finished, the plate is soaked in water for about ten minutes, so as to wash out the greater part of the unaltered bichro mate ; and the superfluous moisture should be removed by dabbing with a piece of soft muslin. All is now ready for the application of the printer's ink, and any ordinary sample of letter-press ink will answer well. A dabber is made by tying a few scraps of rag in a piece of muslin, and a little ink is taken on the face of this, and spread evenly over a slab of metal, slate, or glass. When the ink is sufficiently diffused, and the amount remaining on the dabber is not quite sufficient to make a patch of unbroken black on a sheet of note-paper, all is ready for inking the gelatine film This is an operation requiring some little care and judgment; but no real difficulty is likely to pre sent itself, even to a person who has never handled an inking-roller or worked with printer’s ink. As the image becomes developed—from the adhesion of the ink to the exposed parts of the film, and its rejection by the unex posed portions—it will be found that the inking can be very well controlled by the amount of pressure with which the dabber is applied; heavy pressure depositing much ink, and light pressure either clearing off, or deposit ing, a smaller quantity. When the plate is properly inked, a transfer must be taken on a sheet of paper, and either bank-post, or the ordinary thin French note paper, may be used ; but this paper must, however, be made moderately damp by being allowed to remain for some minutes between sheets of moist blotting-paper. The damped paper is now laid on the inked plate, and contact is established by careful rolling with a small wooden cylinder covered with a stout india-rubber tube, two or three thicknesses of thick paper being interposed between the transfer and the roller. Before stripping off the print or transfer, it is well to slightly sponge the back in order to lessen the tendency of the paper to adhere to the gelatinous film. The trans fer is now laid on the wood block, and pressed into inti mate contact by means of the india-rubber roller, a couple of thicknesses of stout paper being interposed as before. A final rub down should be given with the handle of a tooth-brush or some similar hard body. When the paper is stripped from the block, the ink-photograph will be found adhering to it. The above-described simple method of transferring a collotypic impression to the wood-block will, we hope, be of service to many of our readers, A NEW DEPARTURE IN PHOTO-MECHANICAL PRINTING. When a collotypic picture is transferred to stone for litho graphic printing, or to metal for etching into a typographic block, it generally happens that the details clog up con siderably during the first inking, each patch of fatty matter becoming, to all appearances, considerably extended, and the result is a very notable deterioration. This arises from the circumstance that the stipple of a collotypic print is not sharply outlined, a halo of fatty matter being traceable around each granule of ink, and this halo takes ink when on the zinc or on the stone. An attempt to manufacture photo-typic blocks by producing a high etching from a collotypic transfer was not com mercially successful, as the blocks were far inferior to those obtainable by the Pretsch and other methods. A recent discovery of Mr. Swan gives us a practical method of obtaining a transfer with a grain so clearly and sharply outlined as to print well from a litho stone, or to yield a transfer capable of being inked up on zinc or other metal without sensible deterioration ; and excellent typo graphic blocks can be obtained by then etching the metal plate into relief. We will, before long, insert such a block in our columns, so that our readers may judge for themselves.