Photomechanical print (photochromie using the Léon Vidal process) mounted on cardboard.
Léon Vidal’s Photochromie used a series of registered lithographic colors manually separated, to produce a color image, not necessarily accurate to reality. The different colored inks were printed over each other in registration and then a Woodburytype was placed over them yielding a color print. The use of metallic inks or papers, when dealing with metal objects, such as armor, created startling results. One of the drawbacks was that the prints had to be mounted inside stiff mats due to the need for them to expand and contract with atmospheric conditions. This made it nearly impossible for the process to be used in books. However there are examples of small photochromies that were glued directly to a mount. Maybe it was the size of the large prints that caused the problems. 
This print is from Le Trésor Artistique de la France (Treasury of French Art) a book illustrated by photographs intended to popularize the French artistic heritage and published by the Société Anonyme des Publications Périodiques (Corporation for Periodical Publications). Planning for Le Trésor began in 1876 and publishing began in 1878, and it ceased publication after its initial series, devoted to the works of the Galerie d’Apollon. Compared to similar works and considered in the context of the cultural, technological, and economic issues of the day, the evidence points to the work’s actual mission as the promotion of a new photographic process, an objective that takes precedence over the popularization of artworks. Le Trésor therefore emerges as a representative example of a ‘livre-spécimen,’ or ‘specimen book.’ That it was never completed becomes less a sign of failure than of the changes taking place in the relations between books and photographs at the turn of the 1880s. 
Musée d’Orsay Inventory number PHO 1983 165 538 2
Hanson, David A, and Sidney Tillim. Photographs in Ink: [exhibition], May 1-29, 1996, University College Art Gallery, Teaneck. Teaneck: NJ, 1996. plate 17 (alt).
Laureline Meizel. ”Le Trésor artistique de la France” : un cas exemplaire de “ livre-spécimen ” au tournant des années 1870-1880. Etudes photographiques, Société française de photographie, 2012. Fig. 3
A. Hamber, A Higher Branch of the Art, p. 90
 Hanson, David Checklist of photomechanical processes and printing 1825-1910, 2017
 Laureline Meizel. ”Le Trésor artistique de la France” : un cas exemplaire de “ livre-spécimen ” au tournant des années 1870-1880. Etudes photographiques, Société française de photographie, 2012.