San Georgio from Doges Palace by moonlight Venice Italy, c. 1890s, (M) Library Image

Detroit Publishing Co. Catalogue J, 1905. Print no. 8692. Views of architecture and other sites in Italy

HISTORY OF PHOTOCHROM PRINTS

The photochrom process was initially developed in Switzerland and was spelled without an "e", so the correct original spelling was actually "photochrom". Once the process was introduced in America, the "e" was added to aid pronunciation. A Photochrom is a color photo lithograph, produced from a black-and-white negative. The final prints were created using different color impressions from multiple lithographic stones. The stones used by the publisher Detroit Photographic Company were imported from Bavaria and coated with a special Syrian 'asphaltum' substance that would be chemically sensitized to light, put in contact with a photographic negative, exposed to the sun for up to several hours, then "developed" in oils of turpentine. A separate stone would be made for each color to be used. A minimum of four stones and as many as fourteen stones might be used for a given image.
(Passage: American Photochrom Archive, Image: Library of Congress)