experience soon determines the number of tints required for the particular class of negative. After exposure the plate is removed, placed face downwards on a sheet of black cloth or paper, and the back exposed to the light; the reason for this being to cause perfect adherence to the glass, and to lessen the relief, which takes but a short time and may be determined by the photometer or by the plate assuming a faint brown colour. The plate is washed for some hours in running water, or till, on placing on a sheet of white paper, it has quite lost its yellow colour, and is then dried and ready for printing, or maybe kept in this condition for a long time. For printing, the plate is set horizontally, and covered with a solution, which is ca led the etching solution.
Water ............... 300 parts.
Glycerine ... ... ... ... ... 600 ,,
Ammonia ... ... ... ... ... 30 ,,
Salt.................. 30 ..
This is allowed to act till, on passing the finger gently over the plate, the film seems thoroughly penetrated. The solution is then poured off, and the excess removed with a soft sponge, and the plate is then rather sharply dabbed with a cloth or fine blotting paper. The plate is now ready for fixing on the machine, which may be either the hand or steam press. A mask of stout waxed paper is cut and mounted, so as to cover the margins, and the plate is then inked and printed from. The inking is usually effected with two rollers - the one of leather which is used with a thick ink and heavy pressure to ink the shadows, and the other a gelatine roller with a thinner ink and lighter pressure for the half-tones. The paper on which the proofs are pulled may be of various kinds. It may be glazed or unglazed, rough or smooth surface, India, China, or Whatman's, according to the result desired, and the proofs may be allowed to dry without further treatment, or they may be glazed, which is usually effected by floating the prints on an aqueous solution of white lac, or by coating them with an ordinary label varnish, and drying by the heat of a gas stove, when they present the appearance of ordinary albumen prints. The lac varnish is made by boiling 60 parts of white lac with 1000 parts of water, and 60 parts of borax. The prints are floated for some seconds on this in exactly the same way as for sensitising albumen paper, and