1855, American English, apparently from Greek ambrotos "immortal, imperishable" (see ambrosia), with second element from daguerreotype. A type of photograph on glass with lights given by silver and shades by a dark background showing through.
This invention consists in an improved process of taking photographic pictures upon glass, and also of beautifying and preserving the same, which process I have styled "ambrotype." My improved process has reference to the art of taking pictures photographically on a film of collodion upon the surface of a sheet of glass, the collodion being suitably prepared for the purpose. By the use of the said process, the beauty and permanency of such pictures are greatly increased, and I have on this account styled the process "ambrotype," from the Greek word ambrotos, immortal. ["Specification of the Patent granted to James A. Cutting, of Boston, in the United States of America, Photographer, for an Improved Process of taking Photographic Pictures upon Glass and also of Beautifying and Preserving the same. Dated London, July 26, 1854," printed in "Journal of the Franklin Institute," September 1855]