How To Make Photographic Carbon Tissue

Carbon tissue may be purchased either sensitised or unsensitised. Sensitised carbon tissue will keep for a fortnight, under pressure; unsensitised tissue will keep indefinitely.

To sensitise the tissue, immerse it in a solution of bichromate of potash, and let it dry squeegeed in close contact with glass. This operation is conveniently performed at night, when, if the room is kept fairly dark, the glasses may be placed in the rack over the kitchen fire; in the morning they will be dry. Care must be taken to dry the tissues away from gas or oil fumes, as these make the tissue insoluble. Many good authorities, however, consider that better results are obtained when the bichromate is mixed with the gelatine before coating the paper.

The following is Burton’s procedure: Cover 4oz. of Nelson’s opaque or other soluble gelatine with 15 oz. of water, and allow it to swell for an hour or so; then thoroughly dissolve by placing the jar containing it in hot water. Dissolve 1½oz. of loaf sugar in 2oz. of water, and add to the dissolved gelatine. Next dissolve ¼oz. of potassium bichromate in 3oz. of water, and add to it sufficient ammonia to give it a decided odour; then mix with the gelatine.

The favourite pigment is Chinese ink, but any pigment in a very fine state of division is suitable; it should be broken up, and made into a stiff paste with water. Mix some of this pigment thoroughly with the gelatine in small quantities, stirring vigorously, until more pigment has been added than is necessary to render quite opaque a thin film spread on paper. The support must be a good tough paper that will stand rough handling when wet. Over the top of a trough is then fixed a large glass rod or tube. Two sheets of paper are placed back to back, and, one end being brought under the rod, the solution is poured out until it half covers the rod; by gently drawing the paper round the roller the two outside faces are coated.

Hang up to dry, and the paper is then ready for use.

Cassell’s Cyclopaedia Of Mechanics by Paul N. Hasluck