'double transfer' definitions:

Definition of 'double transfer'

From: GCIDE

Carbon process \Car"bon process\ (Photog.) A printing process depending on the effect of light on bichromatized gelatin. Paper coated with a mixture of the gelatin and a pigment is called
carbon paper or
carbon tissue. This is exposed under a negative and the film is transferred from the paper to some other support and developed by washing (the unexposed portions being dissolved away). If the process stops here it is called single transfer; if the image is afterward transferred in order to give an unreversed print, the method is called double transfer. [Webster 1913 Suppl.]