The Dictionary Of Photography

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

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is done by heat, and the best heater is a proper copper plate heater. Failing this, an ordinary gas stove may be used, or merely a sheet of iron placed over a gas stove. The plate is now placed on the hot plate till the grain melts and adheres firmly to the plate. The sign of the grain being fixed is a peculiar bloom or steely colour, which appears, when looking at the plate, at an angle of about 300. When the grain is fixed the plate should be allowed to spontaneously cool;' and in this condition the grain will not rub off, and the plate may be kept some time. The carbon negative is the next thing to be prepared, and this is printed in the usual way, a safe edge being used. As we wish the margins to be white, it is necessary to use some protecting covering; and the simplest method is to cut a sheet of orange paper the full size of the negative. Out of the middle of this cut a piece the exact size of the desired picture, and from the margin cut another eighth of an inch all round ; and, after the real exposure has been given,, cover the exposed portion with the central cut-out and the margin with the edge. This is best done by pasting the mask and margin on a piece of glass the exact size of the negative. This ensures an insoluble strip of carbon tissue all round the picture. The carbon negative is now deve-loped on the copper plate in the usual way, and when developed and fixed is rinsed with water, then with a mixture of equal parts of methylated spirit and water, and finally with spirit alone till all the water is out of the film. The plate, both margins and back, is covered with black varnish, allowed to dry, and it is ready for etching. The plate is now placed in No. 1 bath of perchloride, and left for one minute ; then into No. 2, where it is left for two or three minutes; then into No. 3 for about three minutes; then into No. 4 for three minutes ; and finally, into No. 5 till the highest lights on the copper are just darkened, and half a minute longer. The plate is now dropped into a 5 per cent, solution of caustic potash, the resist or carbon cleared off, and then the varnish, with turpentine and benzole the plate well washed and polished with whitening, when it is eady for printing from in the copperplate press. Very full-working directions are to be found in Mr. Denison's "Treatise on Photogravure," published by Iliffe and Son. For a list of refer-ences to collateral subjects in this Dictionary, see Photo-mechanical Printing Processes.