Half-Tone on the American Basis

Half-Tone on the American Basis

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This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1896 edition. Excerpt: ...whilst the dots in the shadows appear sharper and denser. The en be turned to for an example of the right appearance. But even in these ways the best negative may not be attained, it being difficult for the operator to choose every time, not only the correct stop, but to guess also accurately the duration of the exposure so that the dots in the shadows possess the necessary fineness. I had occasion to recommend previously that as a rule a little over-exposure was advantageous. In such cases we intensify once as ordinarily with copper and silver, and after washing well, pour over the negative a solution of wineyellow or wine-red iodine in water dissolved by the addition of any iodide salt, for instance, iodide of potassium (iodine dissolving alone in water only in the proportion of 1-6000) until the silver on the surface of the negative is converted into iodide of silver. It is useless, and needless, to pursue the conversion until the whole picture is formed into iodide of silver. As soon as there appears a green sheen in the shadows, the treatment with iodine is interrupted, the plate washed superficially, and a very dilute solution of cyanide of potassium is poured over in one even flow. According to the strength of the solution a quicker or slower dissolving out of the iodide of silver takes place, and it is easy to follow this by holding the negative against a dark object, for instance the bottom of the washing tank. Instead of using iodine and cyanide of potassium separately they can be mixed beforehand, or instead of this a solution of ferridcyanide of potassium and hypo may be used. The ground of the negative becomes clear glass, the dots sharpen, whilst all the granular deposit attacked by the iodide varnishes, and in the shadows a...
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Product details

  • Paperback | 26 pages
  • 189 x 246 x 1mm | 68g
  • Rarebooksclub.com
  • United States
  • English
  • black & white illustrations
  • 1236841395
  • 9781236841391