Autotype.

Autotype. In this process, a sheet of paper coated with a film of dichromatised gelatine, in which lampblack or other permanent pigment has been held in solution or suspension, is exposed to the action of light, in a printing-frame, beneath an ordinary photograph negative. In proportion as the light is admitted to the gelatine film or 'tissue,' through the negative, it becomes hardened and insoluble in water. The print is afterwards treated by washing away the unaltered portions of the film, and the result is a permanent print of the object photographed. The process is admirably adapted for the reproduction of oil-paintings; and the enormous series of autotypes from the chief works in all the great public galleries of Europe, published by the Messrs Braun of Dornach, near Mülhausen, are unrivalled in this direction. The process has also been successfully employed for the reproduction of drawings; but where the work to be copied has a perfectly dead surface—as is the case, for instance, with charcoal sketches—the slight gloss possessed by the autotype print is a disadvantage. This objection is still greater in the reproduction of engravings and etchings; and for these the heliogravure process of M. Amand Durand of Paris is preferable, as here a metal plate is prepared by the aid of photography—more or less supplemented by retouchings by the hand with burin or etching-needle—and can be printed in ink and upon paper exactly similar to those of the original engraving or etching which is being copied. Autotypes, and also heliogravures, can be printed with a margin, without mounting; a great advantage when book illustrations are required, as mounted photographs never preserve a perfectly flat surface, but, with the slightest change of temperature, warp the paper to which they are attached in a most unsightly manner. See PHOTOGRAPHY.