CARBON TRANSFER PAPERS Transfer papers for receiving the film or image in the carbon printing process. Two kinds of such paper are used, called respectively " single transfer paper " and " double transfer paper." The former are those employed when the film or image is transferred from its original paper to one on which it is to remain perma nently ; the latter are used when the film is transferred to a temporary support for develop ment, and re-transferred to a final support as its permanent basis. Single transfer paper is pre pared by coating any suitable paper with gela tine that has been so hardened as to be prac tically insoluble and impermeable. Double trans fer paper bears a thicker coating of soluble gelatine. Both kinds of paper are easy to prepare ; any carbon worker can therefore obtain his favourite paper by preparing it himself.
The easiest method of working for the single transfer process is to coat the paper first and harden the gelatine coating afterwards. A solution of gelatine should be prepared, i oz. being soaked until soft and then dissolved by heat and made up to about 25 oz. The gela tine solution should be applied to the paper as evenly as possible, by means of a flat brush or a sponge. The brush should be taken first along
the sheet of paper, then across, and then diagon ally, so as to avoid ridges and to render the coating even. Many workers prefer to give two thin coatings rather than one of medium thick ness, the second being applied after the first is quite dry. When the gelatine coating' is thoroughly dry it should be hardened by immers ing the prepared paper in a solution of chrome alum, 12 grs. to each T oz. of water. Three or four minutes should be allowed for immersion, and the paper should then be rinsed in two or three changes of water and dried.
For double transfer a thicker coating of gelatine is required, this being obtained by two or three coatings of the solution given for single transfer ; and no hardening solution is employed. Both kinds of paper will keep indefinitely if stored in Lt dry place. The methods of using are given under the heading " Carbon Process." The double transfer paper is often used by photo-lithographers as a photo-transfer paper, and is found to be very suitable for this purpose .when sensitised with bichromate.