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The photographic news
- Bandzählung
- 29.1885
- Erscheinungsdatum
- 1885
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- Hochschule für Grafik und Buchkunst Leipzig
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 1386, March 27, 1885
- Digitalisat
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Zeitschrift
The photographic news
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Band
Band 29.1885
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- Register Index III
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Band 29.1885
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202 THE PHOTOGRAPHIC NEWS. LMARCH 27, 1885. found to have plenty of body, and the image to be rich and brilliant. The gelatine employed is Heinrich’s, that being certainly a very good make, and one generally obtainable ; but it is probable that any ordinary good gelatine will answer. Gelatine 20 grains Bromide of potassium 15 „ Distilled water ... ... ... 2 ounce Let the gelatine soak in the water for a few minutes whilst the bromide is dissolving, then heat up to 130° F., or thereabouts; and stir in, also heated to the same temperature, a solution of— Nitrate of silver ... 20 grains Distilled water 1 ounce A matter of great importance in the preparation and use of gelatine emulsions, is the amount and quality of the light by which the various operations are performed. The need for particular attention to this point arises not only from the very sensitive character of some of the pre parations, but more especially from the length of time — compared with that of the preparation of a collodion plate —to which the gelatine emulsion is exposed to the light of the “ dark-room ” during its manufacture, and during the coating and packing of the plates. For mixing ordinary emulsions, a sheet of yellow paper pinned round a candle will suffice, but it will be well to have a lantern fitted with glass which may be used as the support for one, two, or three thicknesses of golden fabric according to the strength of the light and the sensitiveness of the emulsion in hand. During the coating and setting of the plates, some such lantern is necessary, as the light reflected from the ceiling, in the case of using a candle surrounded by yellow medium and not covered at the top, would be sufficient to affect the emulsion, exposed as it is in large surface, and remaining so exposed forsomelength of time. It is proper, if the lantern is used on or near the coating slab, to have so much additional thickness of golden fabric or whatevar medium is used, on the side which lights the plates whilst on the slab, that there is only sufficient light to see them ; but on the side which lights the plates whilst being coated, there may be light sufficient to see work with comfort. The coating occupies seconds, whilst the setting takes minutes. The silver may be mixed by stirring in with a slip of glass, the gelatine and bromide being contained in a small jug, a cup, or a glass ; or the bromide mixture may be con tained in a flask or phial, and the silver poured in a little at a time, the flask being swirled round the while. In either case, the “ emulsion,” as it is now termed, is placed in a saucepan or boiler, and the lid being replaced, heat is applied till the thermometer shows 150°. After two or three hours of cooking at about this heat, the emulsion is removed from the hot water, and when at a heat just as great as can be borne by the hand with comfort, say from 100° to 120°, is mixed with the following solution, which has been prepared and allowed to reach the same tempera ture meanwhile :—Gelatine, 140 grains, swelled in cold water for half-an-hour, then drain, put in a clean jug, and add 5 ounces of water, hot enough to dissolve it, say at 180°, or higher. The mixture of the cooked emulsion with the gelatine solution must, of course, be made by yellow light, and with good stirring. From half an ounce to one ounce of methy lated spirit is now stirred in, and the emulsion is filtered through a piece of clean cambric, and may be used for coating, as it is; but I prefer to add half a drachm of a solution of chrome alum, made by dissolving twelve grains of this substance in one ounce of water. This solution must be poured into the emulsion whilst being vigorously stirred, otherwise it may cause coagulation of part of the emulsion. The object of using chrome alum is as a safe guard against frilling. This emulsion, which is only a modification of the original one by Dr. Maddox, is one which the beginner in emulsion work is strongly recommended to make as a com mencement of his operations. It is very simple and easy to make, no washing being required, and is not so easily spoiled by want of attention to niceties as some other pre parations. Moreover, the quality of the photographs that may be produced with it is excellent; in the clear ness, “ bare glass,’’ character of the shadows, it reminds one of wet-plate negatives ; the one thing wanting is speed, and in this particular it does not compare with some of the modern processes ; but there are many cases where the quality of high speed is not essential, and where, indeed, such rapidity as was obtainable with wet collodion is quite sufficient. Copying, photographs of still life, land scapes when not instantaneous, transparencies, and portraits in the open air, are some of the uses to which it may be very successfully applied ; whilst there is another advantage to the beginner—that if he should happen to spoil a batch, the cost is insignificant. This argument is perhaps not worth mentioning compared with that of the quality of the result obtainable. If somewhat quicker plates are required, the stewing of the emulsion may be prolonged to six or eight hours, and the bromide of silver still be in a condition in which it bears to be distributed through the large amount of gela tine given. It is not absolutely necessary that the tempera ture should be kept at the fixed point of 150°. To ensure this would require constant care, and some special appli ance. The heat may fluctuate from 170° to 120°, and to keep within these limits is tolerably easy. If there is no convenience for having a gas stove under the boiler it may stand in the dark room, and a quart or so of the water may be taken out occasionally, and replaced by boiling water. Another method is to make the emulsion in an opaque bottle — 1 have made many experimental batches in ginger beer bottles—and when mixed and corked the bottle may stand in a boiler on the kitchen hob. In this case, if any emulsion is seen to lie round the cork, it must be removed before pouring the emulsion out of the bottle, as on account of having been exposed to light, it is unfit for mixing with the stock in the bottle. When ginger beer bottles are used, great care must be taken to thoroughly clean them with hot water and a bottle brush, after each batch is made; as a very little old emulsion might set up various evils in a new batch. For spreading the emulsion on the plates, a slab of glass must be carefully levelled, and the plates laid upon it to “ set ” as they are coated. The most convenient method of coating is to pick up the plates in a pneumatic holder, and pour a good sized pool of emulsion nearly on the middle of the plate; and then, by slow movement, allow it to run successively to each corner of the plate, and pour off the surplus into the coating vessel. Emulsions of different makes require that different quantities should be left upon the plates. If the coating is too thin, there will be halation or a fogging round the high lights. With the formula given, the plates will have a sufficient coating if each ounce is made to do for six or seven quarter or three half-plates. As a way of ensuring this quantity, the emulsion may be measured on to the plates with a silver teaspoon, which commonly holds rather more than one drachm, but then there is not sufficient for it to flow readily to the corners of the plate, and it must be assisted by the back of the spoon—not rubbing against the glass, however—or by the tip of the finger, or a glass rod. When the plates are “ set,” so that upon being stood up right the emulsion does not run, they are ready to be stood up to dry. The drying should take place in absolute dark ness, and to ensure this in an ordinary household without some special appliance is not very easy. If a dry cupboard is available which can be rendered quite light-tight by hanging curtains over the door, cover ing the joints and keyhole, that will suffice. It must of course only be opened at night or when no light but that of the yellow lamp illuminates it. A small number of plates may be dried in dry weather in large box or chest of drawers, taking care to cover the lid of the box or the front of the drawers with opaque cloths.
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