The Dictionary Of Photography

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

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Emulsion
strong silver solution in quantities of about half an ounce at a time, shaking as before after each addition, and, when all is added, give a final, thorough shaking for, say, a couple of minutes. Now put the bottle into the pot of hot water, see that the stopper is not jammed in, and put on the lid. Light the gas, and boil up as quickly as possible. If the water was previously boiling, and the gas only turned out for the mixing operations, it should boil up in less than 5 mins. ; then keep boiling for 59 mins. At the end of this time turn out the gas, take off the lid, take out the bottle, and remove the stopper at once, or you will not get it out afterwards. The bottle must now be cooled down as quickly as is consistent with safety to the glass. In very cold weather it may stand on the table for 10 mins. or so, and then be cooled with water ; or, in any weather, place it in a pan of nearly boiling water, and cool gradually by allowing cold water to trickle slowly in, shaking the bottle occasionally. Whatever method is adopted, it should be down to 900 F., or lower, in 15 or 20 mins. at the most It cannot easily be made too cold, as the gelatine has lost its power of setting. In a glass beaker (about 12 or 14 ozs. size) put 1 oz. of Nelson's No. 1 Photographic or " X opaque " gelatine, and pour over it 10 ozs. of clean ordinary water. Leave it to soak until the gelatine has absorbed 4 ozs. of water, pour off the surplus 6 ozs., melt the swelled gelatine by immersing the beaker in hot water, and pour it into the 20-ounce bottle containing the cooled emulsion. Shake up well, and pour all back into the beaker, draining out the bottle thoroughly. Leave it to set in a cool place for 24 hrs. It has next to be washed. The addition of the gelatine after boiling should be made when the boiled emulsion and dissolved gelatine are both at as low a temperature as possible, and between the time of this addition and that of washing the emulsion it should be kept as cold as possible. For the washing clean ordinary water at a temperature cooled down to below 40 degs. by melting ice in it, should be used. In a glazed earthenware pan or other suitable vessel put about 3 pints of cold water, and add 3 ozs. of saturated solution of potassium bichromate (made by saturating clean ordinary water with the bichromate). Before squeezing the set emulsion through the canvas it should be cooled down so as to be as firm as possible. The water into which it is squeezed will then remain almost clear, or but slightly milky. If the emul-
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