The Dictionary Of Photography

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

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Emulsion
beaker of distilled water, stirring frequently during the course of an hour. If, however, it is inconvenient to give so much time to it, the simpler way is to collect all the dice on a piece of well-washed calico, gather up the loose ends and tie them together, and suspend the little bag thus made by the aid of a piece of string in to a glass rod; place this across the mouth of a decent-sized beaker or jar, fill the jar sufficiently full with distilled water to cover the bag, and leave it for an hour or two. The water filling the bag extracts the useless nitrates and excess of bromides, and being heavier than the pure water sinks to the bottom of the vessel, so that there is always a current of water less heavily charged, and the washing is mechanically performed. After about two hours of this soaking, the water should be changed, the bag being allowed to drain well before the vessel is refilled. Washing may thus be effected very thoroughly in from six to eight hours, or comfortably in a day. Twenty-four hours is not actually too much - in fact, very strongly recommended by Eder and other authorities. If a good supply of water is to be had, the washing may be performed by fixing the vessel under a tap, and allowing the same to run on it all night, but personally I think it is better to use distilled water even for washing the emulsion. There is one method of washing the emulsion which is, I believe, rarely used by commercial makers, and that is by the aid of alcohol, as was noted in speaking of Henderson's emulsion process. As soon as the cooking is finished, the still warm and liquid emulsion is poured into three or four times its quantity of alcohol, and well stirred round. The extraction of the unneces-sary salts is not so complete and is more costly than when washing is effected with water, but it is of advantage in saving time and there is less chance of frilling in the subsequent operations ot developing, etc. After washing by this method, it is essential to allow the emulsion to soak in water for an hour, in order that it may absorb the necessary amount of water. When the emulsion has been sufficiently washed, it should be collected on a piece of clean and well-washed linen, allowed to drain, and gently squeezed so as to press out the superfluous water, then collected and melted by placing it in a beaker or other convenient vessel, which should be placed in a water bath. Care should be taken not to heat the emulsion too much, or else it will become fogged and useless, and the more rapid the emulsion the less heat it will
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