The Dictionary Of Photography

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

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Emulsion
emulsion very gradually, with shaking between each addition, and this addition may be made either before or after filtration, preferably after. Many workers add a little alcohol to the emul-sion, to make it flow over the plates ; and it is, I think, to be recommended when coating is to be done by hand. One part of pure rectified spirit of wine to every twenty parts of emulsion is the right proportion. The necessary utensils for coating plates may be either very simple, or more or less elaborate, according to the operator's ideas. The one absolute essential is a levelling stand, and if we are going to coat any quantity of plates, a good-sized sheet of plate glass and a level. All these may be bought from any photographic dealer, or the glass alone obtained from any glass warehouse. Sheets of glass of the necessary size, we need not say, are also essential. The glass on which the emul-sion is to be spread should be well cleaned, and for this purpose tripoli made into a paste with methylated spirit may be used, or prepared chalk made into a thin cream with water. After rub-bing the glass well with either, it should be rinsed in tepid water, then well rinsed again in hotter water, and given a final rinse in hot water, when it may be placed in a rack to drain, and, if thought necessary, polished with a soft wash-leather, which has been freed from grease by washing in soda. When the glass is cleaned, each piece should he taken up by means of a pneumatic holder, which may be obtained from any photographic warehouse, and examined for flaws and large bubbles ; all defective pieces being rejected. The glass should be piled together and heated by being placed in an oven or before the fire for a little time. It must not, however, be made too hot, only just pleasantly warm, so as not to chill the emulsion when it is poured on. A measure may also be used by the amateur in his first trials to measure out the quantity of emulsion, but with a little practice one is soon accustomed to pouring out about the right quantity. The method of coating depends upon the size of plate; with small plates - for instance, half and quarter plates - it may be poured into the middle of the plate, which is supported by the pneumatic holder, and then the emulsion made to run to the four corners by tilting the plate as when coating a plate with collodion. This, however is not a very easy matter, and it is far simpler to pour the emul-sion in a line right across the plate, and spread by means of the simple little distributor shown in fig. 49, which is a piece of
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