The Dictionary Of Photography

A True Historic Record Of The Art & Practice Of Photography 100 Years Ago.

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Collotype
bring prepared at once, on sheets of plate glass, which should be about fths inch thick; the edges and corners should be ground off. This glass is grained, and it is usual to grain two at once by placing some emery flour moistened with water on one, which should be laid absolutely flat on a table, and placing another plate on top, and working this about till both surfaces are evenly grained; care being exercised to keep the emery moist. As soon as the surfaces are ground, the emery is washed off and finer emery flour used in the same way till the surfaces look perfectly homogeneous and free from deep pits or scratches. The plates are then thoroughly washed, rinsed in distilled water, and set up to drain. To ensure adherence of the gelatine to the glass during the hard usage to which it is subjected in printing a substratum is required. This is usually a mixture of beer and silicate of soda or potash. The beer to be used is that known as " four ale," and it should be allowed to stand twenty-four hours to get perfectly flat. The mixture is
Four ale ... ............200 parts.
Silicate of soda (syrupy)......... 10 ,,
This mixture is well stirred, allowed to stand for some time, and then filtered through nainsook, well washed previously, and it is ready for use. The plates are heated gently in a collotype drying oven, and then rinsed with a little weak ammonia water, and allowed to dry ; or else, after being dusted, they are flowed over with the silicate mixture, the excess being allowed to run off into the sink, drained for a minute, and a second coating given them, when they are placed in the oven in which they very soon dry. Another substratum, lately recommended by Holzhausen and Wetherman, is
No. 1.
Dextrine       ... ... ... ... ...      40 parts,
Sugar            ............... 5 ..
Alcohol         ............... 5 ,,
Water           ...............      40 ,,
No. 2.
Silicate of potash (liquid).........1200 parts.
Tannin          ............... 2-5 ..
Dissolve the dextrine and sugar in the water, and add the alcohol
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