Transposing—Black and White.
A modification of the foregoing process may be utilised for the reversal or transposition of black to white, or vice versa, of any subject of which a print may be obtained in printing ink.
An Impression is first obtained either upon sensitised carbon tissue or, preferably, on a thinner paper, coated and sensitised as for photo-lithography. Such paper must not be submitted to a light of much actinic power during or before printing, and as much ink as possible should be used without risk of filling up the work.
Dust Over the impression while still wet any dense opaque colour, applied by means of wool or camel-hair brush, carefully going over every part and piling on as much colour as possible, after which
Expose the Paper bearing the print so treated to the light for a short period, dependent upon the light and sensitiveness of the paper. If it be a full impression, well dusted, the latitude in exposure will be very considerable.
Ink Up the whole surface of the paper with lithographic transfer ink, thinned with turpentine, and applied by means of a sponge or roller.
Develop, as in photo-lithography, either by means of warm or cold water, according to the coating upon the transfer-paper. The sensitised paper, where protected by the ink impression, has not been hardened by the action of the light, and readily parts with the ink and colouring matter. If the impression has been one from ordinary type it will now show in the form of white letters on a black ground.
Transfer to Stone, and otherwise treat as an ordinary photo-lithographic transfer.