Regular transparency gelatine dry plates are the handiest for making positives, especially for amateurs, if one does not care if the subject is in reverse, or if one has a reversed negative to work from. There is a "special" carbon tissue, price $4.00 per roll of 2 × 12 feet, made by the Autotype Company, of London, England, with full instructions appended; by a system of double transfer, reversed negatives may be obtained with this tissue. The "special" tissue is only to be used for the transparency. A safe edge of black paper is required on the transparency, pasted up exactly to the edge of the picture, on the glass side; it comes, sold in strips, gummed, ready for use, about 1/4 inch wide; this is required, as the tissue used for the negative resist on the copper plate, which is printed from the transparency, must have a safe edge, shielded from the light, or it will not attach itself to the copper plate, the tissue coming inside half way. The screw pressure printing frame should have a piece of heavy felt for backing the transparency.
The following instructions for making carbon transparencies will no doubt be found useful:
The carbon tissue prepared for this process consists of paper coated with gelatine containing carbon, lamp-black, or other pigments.
The Autotype Company, of London, manufacture a special "transparency" tissue.
CUTTING UP THE TISSUE is performed by unrolling it gently upon a zinc cutting plate, cut square and true, with the inches marked at the bottom and right-hand side. By using a T square and observing the numbered inches marked on the plate, it will not be difficult to cut the tissue to any dimension. If the tissue is very curly and unmanageable it should be kept down with convenient weights. After cutting it up to the required sizes, which should be conveniently smaller than the dish to be used for sensitizing, it should be kept flat under a metal plate.
SENSITIZING THE TISSUE is the next operation. This is performed in a solution of potassium dichromate rendered alkaline with ammonia. Tie over the mouth of a two-gallon jug a piece of muslin, to form a kind of bag, into which place fifteen ounces of potassium dichromate, then fill up the jug with water and allow it to stand until the dichromate is dissolved and the solution becomes cold. It is sometimes advisable to regulate the quantity of dichromate. In hot weather, or for very thin negatives, the proportion of water should be doubled, while for very hard negatives only half the quantity should be used. In very hot weather it is often advantageous to replace about 30 per cent. of the water with the same quantity of alcohol.