The Practice of Collotype

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American photographic publishing Company, 1935 - Collotype - 96 pages
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Page 17 - ... HYDROXIDE (CAUSTIC POTASH) is very similar to caustic soda and is prepared in the same way. Fifty-six parts of caustic potash are chemically equivalent to forty parts of caustic soda. Both caustic soda and caustic potash should be dissolved in cold water when solutions of either chemical are prepared, because on mixing, considerable heat is evolved and the solution, if too hot, is apt to boil and spatter on the hands or face causing serious burns.
Page 91 - ... oxidation of chromium salts. It forms orange-red crystals, stable in air, and easily dissolves, yielding a yellow solution. It is obtained in a pure form by crystallization. Potassium bichromate is used in photography both for bleaching negatives and for sensitizing gelatin, fish glue, etc. When gelatin containing bichromate is exposed to light it becomes insoluble in water and in this way images may be obtained in insoluble gelatin.
Page 90 - LITHOGRAPHY. lithography — The process of drawing designs on stone with a special crayon or chalk, and of producing printed impressions therefrom; also any process based on the same principle in which a thin flexible metal plate is used instead of stone, called offset printing.
Page 21 - Hard gelatine absorbs from seven to nine times its weight of cold water; soft, from four to six times. Reliable hard gelatines are Nelson's X Opaque, and Number 2 Photographic; Coignets' Super-Photo, and Gold Label; Heinrich's; Simeon's Swiss.
Page 17 - In the avoirdupois system a 10% solution of a solid is made by taking one ounce and making up to ten ounces with water. Converting these figures into grams and cc. we have, roughly, 30 grams in 300 cc. or a 10% solution. A 10% solution of a liquid in water is made by taking 10 ounces or 10 cc. of the liquid and adding water to make 100 ounces or 100 cc. respectively.
Page 31 - ... will read from right to left instead of from left to right. If a film negative is used, it is necessary only to print through the back of it to reverse\.

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