The Photographic Times Volume 5

The Photographic Times Volume 5

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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1875 edition. Excerpt: ...Marechal, of Metz, in France, made an advanco which was then considered wonderful. Their method was to coat metallic plates with gelatin, and bichromate or trichromato of potash, or ammonia, and bichloride of mercury, then again coated with soaps of silver, exposed to light through a negative; then washed, inked, and printed from in a lithographic manner. In a paper read before the French Photographic Society, in May, 1867, Tessie du Motay says: "A mixture of isinglass, gelatin, and gum, evenly spread upon a well-polished metallic surface, and previously treated with an acid chromnte, has been found to give the most satisfactory results. "The ordinary chromate and bichromate salts are not suited to the purpose, as they do not impart sufficient sensitiveness to a mass of organic matter if the latter happens to be of a notable thickness, the photographic image being insufficiently developed, and therefore imperfect; the alkaline trichromates, when used alone, are likewise incapable of producing perfect impressions, LBA COLLODION. with bichloride of mercury, may likewise be used, as also chrome-mercurial salts; but by these means an image is obtained which produces negative prints, so that the photograph must be inverted if it is desired to obtain positive impressions. "When treated with a reducing sait, the trichromate, as also the chromo-mercurial salts, have the property of acting upon the composition of isinglass, gelatin, and gum, when in contact with a surface of copper, rendering that portion of the compound which comes in contact with the metal perfectly insoluble, a result which is accelerated and more completely brought about by warming the film previously to its being flowed upon the metal plate. "After coating, more

Product details

  • Paperback | 46 pages
  • 189 x 246 x 3mm | 100g
  • Miami Fl, United States
  • English
  • black & white illustrations
  • 1236621166
  • 9781236621160