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The photographic news
- Bandzählung
- 27.1883
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- 1883
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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. 1315, November 16, 1883
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Zeitschrift
The photographic news
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Band
Band 27.1883
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- Titelblatt Titelblatt I
- Register Index III
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Band
Band 27.1883
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November 16, 1883.] THE PHOTOGRAPHIC NEWS. 723 referred to find that when water containing flowers of sulphur is distilled, sulphur, insoluble in carbon bisul phide, is found in the distillate ; but if air is excluded from the apparatus, a clear distillate is obtained. The distillate becomes turbid, and deposits sulphur on exposure to the air. It gives a white precipitate with lead acetate, soluble in acetic acid, and with mercurous nitrate a yellow pre cipitate, which soon blackens. It bleaches potassium per manganate. Hence it appears that lower sulphur-acids are formed by the action of water on sulphur. The solubility of arsenious sulphide in boiling water is probably due to the formation of an oxysulphide of arsenic, as such a com pound is produced by boiling arsenious oxide and sul phide in water. THE WOODBURYTYPE PROCESS. (Second Article.) We propose to treat of the old method of Woodburytype, in which the lead moulds are made with the aid of the hydraulic press, before considering the recent develop ments of the method. Let us suppose that we are going to prepare four sheets of sensitive tissue of whole-plate size. The first thing is to select four pieces of plate or patent plate glass of the requisite size, and after having cleaned them, to make a diamond scratch upon one side of each, so that the reverse or back of each plate may be recognized at a glance. The face of each plate is first rubbed over with a little powdered Trench chalk, a piece of soft rag being employed for its application ; and after all excess of the powder has been dusted off by means of a camel’s-hair brush, all is ready for the collodionizing of the plates. The collodion should be made by dissolving ten grains of a tough pyroxyline in each ounce of a mixture of equal parts of alcohol and ether, and after the unmarked side of each plate has been coated, the films are allowed to dry per fectly. In order to make a quantity of the sensitive gelatinous mixture which will serve for coating the four plates, we take If ounces of Nelson’s transparent sheet gelatine, and soak it in 4 ounces of water, after which sufficient heat is applied to melt the mixture. Half-an-ounce of sugar, 80 drops of ammonia solution, 50 grains of glycerine, and 1 drop of phenol are added ; after which, 1 grain of Indian- ink which has been rubbed up with 1| ounces of water is stirred in. The mixture is next sensitized by the addition of 150 grains of powdered ammonium bichromate, and as soon as this is dissolved, the mixture is stiained through muslin. The four plates are now very slightly warmed, and levelled, with the collodionized face upwards, after which one-fourth of the total quantity of sensitive preparation is poured upon each, care being taken to spread the mixture over the entire surface of the plates before the gelatine begins to set. As soon as the coating has thoroughly gela tinized, the plates are placed, face downwards, over the chloride of calcium, in the apparatus figured on page 582 of the present volume. Chloride of calcium can be easily pur chased in small quantities from dealers in chemicals; but it ordinarily requires to be dried before it is used for our purpose. To dry it, an ordinary cast iron saucepan is about half filled with the crude article, and is placed over a clean fire, or large Fletcher’s gas stove, until aqueous vapours are no longer given off. The chloride is now cut or broken into lumps of a suitable size by means of a hammer and chisel, when the lid is placed upon the sauce pan, and the whole is allowed to cool. The cold chloride of calcium is transferred as quickly as practicable to the trays, and the drying-box is closed. The chloride of cal cium which has served in the drying-box is once more dried as directed above; and, when cold, it should be stored in a perfectly closed bottle. Whenthe tissue is dry, the point of a penknife is run under the collodion film all round the edge of the sheet, after which the whole can be stripped from the glass with very great ease. The tissue is exposed with the collo dionized surface next to the film of the negative, and it is well to provide the negative with an opaque border, so as to leave the extreme edges of the sheet of tissue unexposed, and consequently soluble. It is also advisable to dust over the surface of the tissue and the face of the negative with powdered French chalk, all excess being removed by a camel’s hair brush. This serves to diminish the chances of adhesion between the negative and the tissue during a long exposure, and it is also necessary to guard against the possibility of any damp reaching the tissue by laying either a sheet of tinfoil or other waterproof material over the tissue when in the printing frame. The time required for the exposure varies from about twelve minutes in full sunshine, to a day or more in dull weather ; and it is possible to judge of the progress of the exposure by an inspection of the tissue, as when the lighter shades of half-tone are visible, the action of light has been carried far enough. It is, however, undesirable to open the printing-frame for inspection, as damp may gain access to the tissue; and for this reason, most practitioners prefer to use some form of actinometer. The actinometer or photometer of Woodbury is a metal box containing a band of sensitive silver paper, which can be drawn out over an opening. It is exposed by the side of the printing-frame until a standard tint is registered. In order to adapt the instrument for the registration of long exposure, screens of coloured gelatine are provided, which, six- eight- or ten fold, the exposure required for the registration of one tint. Of course, practice alone can enable the Woodbury typist to judge the exposure required for any particular nega tive. The amount of Indian ink used in making the tissue may be varied according to the degree of relief re quired, thicker reliefs being obtained as the proportion of Indian ink is reduced. Rather dense negatives should be used for Woodburytype where practicable, as otherwise it is difficult to obtain sufficient relief, even when the pigment is either reduced to a minimum, or altogether omitted. It may be noted that quicklime may be used in the dry ing box in the place of chloride of calcium ; for this pur pose clods of freshly-burned line should be selected, and after having been broken into fragments of a convenient size, the material should be preserved in carefully closed bottles. In our next article we shall detail the manipulations incident to the development of the relief, or the dissolving away of the superfluous gelatine by means of warm water. Sensitive Woodburytype tissue is very prone to become insoluble by the action of other agencies than light. When sensitive tissue is preserved for any considerable length of time, insolubility slowly sets in, especially if traces ofmoisture ate present. Any substance which exercises a deoxidizing or reducing action upon bichromates tends to cause insolubility ; hence, tissue which has been exposed to the products of the combustion of impure coal gas is fre quently found to be insoluble ; and the gases or vapours evolved from putrefying bodies also tend to reduce the chromium compound, and cause insolubility. STUDIO FURNITURE. Those familiar with British and Continental studios can not fail to remark a decided difference that exists between the two, in the matter of furniture. While we are given to crowding the studio with accessories, our neighbours across the silver streak rarely do anything of the kind. It is, indeed, passing strange to enter the glass room of a high and mighty firm like that of Van Bosch, on the Paris Boulevards, or of Benque, in the Boissy d’Anglas, and find scarce a stick of furniture besides the posing chair. It is
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