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The photographic news
- Bandzählung
- 27.1883
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- 1883
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- Englisch
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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. 1290, May 25, 1883
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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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May 25, 1883. J THE PHOTOGRAPHIC NEWS. 325 exposed negative by saying that it required more bromide, when, in reality, the quantity used was very much in excess—some thing like two grains to the ounce. What the plate in question required was less bromide and more pyro. PHOTO-LITHOGRAPHY AND PHOTO ZINCOGRAPHY. BY MAJOR J. WATERHOUSE, B.S.C., Assislant Surveyor-General of India. Chapter X.—Principles of Lithography, and Materials Required. We now enter upon the purely lithographic part of our sub ject, and though it is beyond the scope of the present papers to go fully into the details of lithographic printing, which forms quite an art in itself, and can only be properly learnt by long experience, we propose to give a short notice of the theory and practice of lithography sufficient to give an idea of the methods employed. For those who wish for further information, we may refer to Richmond's “ Grammar ” (already noticed), to Roret’s Manuel de VImprimeur Lithographe, and to the very practical series of articles by Mr. T. Bolas, published some four years ago. Lithography and zincography both depend on the same principle of the mutual repulsion of grease and water, and on the fact that though the surface of the stone or metal plate will readily absorb either grease or water, it will not take both in the same place. Thus, if a stone or zinc plate be wetted, and a roller charged with printers’ ink be passed over it, none of the ink will adhere to the wetted surface, though it will on the dry ; and, on the other hand, if a stone or plate be touched, however slightly, with any greasy substance, and then wetted, it will be found that the greasy parts will repel the moisture, but will readily take up printing ink from a roller passed over them. Greasy matter not only adheres very firmly to the stone, but has a powerful tendency to spread itself in all direc tions, through its porous substance, and if this tendency were not counteracted by filling the pores of the stone with some other material such as gum, which is imperme able to and non-absorbent of grease, the fatty principle of the ink, forming the lines of the photo-transfer print or other design on the stone, would gradually spread, and on applying printing ink, the lines would appear widened, and thewhole design blurred and heavy. It is the prac tice therefore, after making the transfer, to etch the stone and’make it ready for printing by applying weak acid and gum-water, either singly or together. The acid opens and prepares the pores of the stone, so that the gum enters more readily into intimate combination with it, and acts more effectively in confining the greasy ink in its own proper bounds. This combination is so complete that no amount of mere washing with plain water will remove the gummy coating; and if a stone once properly gummed be allowed to dry, and an inked roller passed over it, the ink deposited may be all removed by washing with wet sponge, or even by passing the sponge over the inked part, and then working the roller over it smartly. Con sequently, before any additions or corrections can be made on a gummed stone, all traces of gum must be removed by washing with clean water, and then treating the parts with weak acid, so that they may regain the faculty of absorbing the fatty matter of the ink. The gummy coat ing also retains the moisture on the surface of the stone. With zinc plates the principle is exactly the same, though the metal is not so absorbent as the stone, and, instead of nitric acid, a mixture of phosphoric and gallo-tannic acids is used with the gum, which forms an insoluble and perma nent grease—resisting coating to the plates in the parts untouched by the greasy transfer ink. Lithographic or zincographic printing consists, therefore, of alternately moistening the white and gummed parts of the stone or plate forming the ground of the picture, and re newing the printing ink on the black or coloured parts forming the image, in proportion as it is taken off by the paper at each impression. Simple as this may seem, success depends upon a number of variable conditions connected with the state of the print ing rollers, ink, temperature, &c., which require considerable experience and skill to master. These conditions will be treated of in their proper places. LITHOGRAPHIC Materials, etc. For transferring and printing, a certain amount of litho graphic outfit and materials will be required, the extent of which will of course depend on the amount of work to be done. For small work or amateurs’ use, convenient sized presses, with all necessary materials and instructions for their use, can be obtained from Messrs. Waterlow and Co., and the dealers in lithographic presses and materials. A large number of portable lithographic presses of various kinds are manufactured in Paris. One of the best and most suitable for zinc, stone, or collotype printing is the phototypic press made by Poirier, 122, Faubourg, St. Martin, which is so well constructed that glass plates of any thickness may be passed through it without breaking. For larger work, proper lithographic presses and the other appliances of a printing office will be necessary, and are all obtainable at the dealers. The following is a list of the most necessary articles : — Lithographic press, complete with scraper and tympan leather. For zinc printing a wooden block, about three inches thick, will be required to support the plates. This must be carefully made so that it may be of equal thickness through out, and not liable to warp. A lithographic stone or a slab of slate is sometimes used instead of the wooden block. Stones or zinc plates as required. Trolly for moving stones. Mill-boards or elastic bedding made of felt or kamptulicon, &c., to place below the stone. Glazed boards, made from well-rolled six-sheet cardboard, and used as backing sheets over the printing paper in order to protect the printing paper and outer edges of the stone from any dirt or grease which might be communicated to them from the tympan leather, and also to protect the tym pan leather from any traces of printing ink which might be left on the edges of the stone. Their elasticity also helps the printing. Inkinq tcd>le, with inking slab, made of marble or stone. These are sometimes made of iron, but are better made of wood, so that the under part may form a cupboard, in which ink, rollers, &c., may be kept and preserved from dust. Inking rollers, with leather handles. Midler, for grinding ink—usually made of marble. Palette knife, seven to nine inches long, for mixing ink and applying it to the rollers, &c. Kitchen knife, with blunt edge for scraping rollers. A glazier’s putty knife is sometimes recommended for thir purpose. Sponges.—Of these, several will be required, two er thre of medium size, and grain for washing the stones, damping paper, &c., and small fine ones for applying gum and acid. New sponges must be carefully freed from sand and shelly grit by beating and soaking in weak hydrochloric acid. Care must be taken to keep sponges clean, and in good order while in use. Camel's hair brush, about 4 inches wide, for applying etch ing solution to zinc plates. Damping cloth, for moistening the stone or plate after each impression. This is best made from old linen, sheet ing, &c., and should be soft and free from fluff when wetted. It is folded so as to form a pad rather larger than the hand. In India we use a soft, thin, country-made, cotton cloth. Squeegee, made of a slip of vulcanised india-rubber, set in a wooden handle, is recommended by Richmond for re moving moisture from stones or plates. Blotting paper.
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