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paper, bath, grains, required, printing, nitrate and sensitizing

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PRINTERS' INDICATOR.—A small brass instrument that can be attached to printing frames. It contains two dials with figures, and two movable hands ; one hand indicates the num ber of prints required from the negative, and the other the number already printed.

PRINTING.—This term is applied to a very large variety of methods of obtaining positive pictures from the negative, on paper, glass, wood fabrics, and other suitable materials. The prin cipal process of positive printing is that known as the albumenized paper process, and it is that method which will be treated upon here. The other methods of printing upon bromide, platino type, gelatino-chloride, and other papers, as well as upon glass, wood, silks, etc., are all treated upon under their respective headings.

The Printing should be as large as possible, well ventilated, well lighted, and with suitable heating arrangements for the winter months. The temperature should be kept as nearly even as possible, as heat and cold have considerable effect upon paper and chemicals. The sensitizing room should also be well ventilated and lighted by yellow windows or by gas light. Both rooms should be kept scrupulously clean.

Under Albumenized Paper will be found the method of preparing the paper with albumen containing a chloride. This can be, and is, usually bought ready prepared. The next process is to sensitize it by floating on a bath of silver nitrate. The usual bath is made up as follows Silver nitrate 40 grains Water i ounce In summer the strength of the silver should be slightly decreased, and in winter slightly increased ; in the one case 35 grains to the ounce being used, and in the other 45 grains.

The addition of other nitrates to the sensitizing bath is often recommended for various brands of albumenized paper. The commonly used formula is this : Silver nitrate 40 grains Ammonium nitrate 20 grains Water i ounce To this a few drops of ammonia are added till the solution is slightly alkaline. To the same bath the addition of five grains of lead nitrate has also been recommended.

On this bath the paper is floated for from forty to eighty seconds in the summer, and from seventy to 120 seconds in the winter, and afterwards hung up to dry. For further details of the

sensitizing manipulations see under Sensitizing.

The Drying Room should be kept quite clean, and heated with a small stove, over which should be hung a rack fitted with wooden clips to suspend the paper. Drying the paper spon taneously is undoubtedly a mistake, as the silver then sinks into the paper, and, the brilliancy of the surface is lost.

printing many operators subject the sensitive paper to the fumes of am monia. By this means much richer and finer tones are obtained. The paper is placed in a box having a false bottom perforated with holes, and beneath which is laid a tray containing strong liquor ammonia. It is very necessary that the fumes be equally distributed on the paper to avoid patchy and unequal prints. In damp weather it may be found advisable to slightly dry the paper before fuming.

Cutting the is best done with an ivory paper-cutter. Many operators cut the print to the exact size required for the finished print. This is not advisable, however, as the subsequent operations will very often destroy or mar the edges, and much loss is sustained in consequence. Never try to secure too many prints from one sheet of paper, but allow of a com fortable margin above the size of the print required.

The attempting to make prints from an negative it should be carefully studied, and the best method of treatment thought out. Thin negatives should be printed in a soft, weak light. A piece of white tissue paper stretched over the frame will secure the required effect.

Weak, flat negatives should never be printed from unless necessary. They can sometimes be improved by coating the back with a varnish tinged with iodine. The varnish is then scraped away behind those parts required to print deeper, and those parts required to print lighter may be treated with the pencil or Indian ink. Another method is to paste a piece of tissue paper be hind and work upon it with the pencil. A strong bath should be used in sensitizing, and the time of fuming doubled. By printing under green glass greater contrast is obtained. See Green Grass.

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