The term " Chromotype " was coined in the 1960's by master photographer Roger Kockaerts, known in the United States as Roger Coqart, to designate multi-colored film prints, fixed onto a high quality paper base. The filmbased positive prints are hand- or spray colored on the emulsion side and permanently fixed onto high quality paper of archival quality by double-sided tape. Chromotypes are essentially stable because no air can react with the silver emulsion and induce image deterioration.
At the beginning of the 20th century Edward Curtis introduced the Orotone photograph which consisted of a positive silver - gelatine image on glass, backed by a gold medium and sealed in a wooden frame. Under specific lighting conditions the orotone glitters like a solid golden object. The orotone process (goldtone, Curt-tone, dorotone), has not been fully documented in the past. It is well known that different American photographers (Edward Curtis, Norman Edson, Arthur Pillsbury) used the orotone process between 1900 and 1920.cc
Edward S. Curtis  (1868-1952) used the orotone principally for a series of portraits of North American indians. He describes  his orotones more under an aesthetic than a technical angle. The general bibliography mentions that the gold tone was obtained by putting gold leaves on the back of the silver-gelatin glass plate, by backing with gold paint or with a medium of gold dust and banana oil. A commercial brochure from 1903  describes that the backing consisted of a combination of banana oil and bronze powders.
The 1903 catalog was created by Curtis to promote his "Curt-Tones". The catalog illustrated 32 different images which were offered for sale in a beautiful frame especially conceived for the orotones which could be obtained in different sizes and prices: dimension 8x10 inch, framed $10 to dimension 18x22, framed $50.
In a relative recent study (2005) at the Art Department of the University of Delaware , Richard Stenman researched a series of orotone photographs by different photographers of the beginning of the 20th century. The technical analysis was made by using ultraviolet fluorescence, x-ray fluorescence (XRF), Fourier-transform infrared spectroscopy (FTIR), et scanning electron microscopy coupled with energy dispersive x-ray spectroscopy (SEM-EDS).
The emulsion layer consisted of gelatin and/or collodion. In each of the examined gold tone layers, bronze powder containing copper and zinc was used. This corroborates the description of the Curtis Studio brochure.
The gold tone of the Chromotype, also called "orotype", introduced in the sixties, uses a chemically inert polyester film with a silver-gelatin emulsion instead of the traditional photographic glass plate. The positive image is treated with the standard archival techniques. The gold tone is realized with the aid of a gilding medium containing bronze powder. Orotypes are permanently mounted on 100% cellulose paper.
 www.soulcatcherstudio.com/.../curtis_cron.html Edward S. Curtis and The North American Indian A detailed chronological biography
 http://www.edwardcurtis.com/ Curtis wrote: "The ordinary photographic print, however good, lacks depth and translucency. We all know how beautiful are the stones and pebbles in the limpid brook of the forest, yet when we take the same iridescent pebbles from the water and dry them they are dull and lifeless; so it is with the orthodox photographic print, but in the Goldtones all the translucency is retained and they are as full of life and sparkle as an opal."
 Advertising brochure for the Curtis Studio, 1903. Edward S. Curtis perfected the medium regarded as Goldtone or Orotone to the extent he eventually named these images after himself calling them "Curt-Tones". Most photographic prints are a positive image on paper. The Curt-Tone process Curtis used was created by taking a clear plate of optical glass and spread a liquid emulsion onto the surface of the plate. Curtis then projected his negative onto the glass to create a positive image. The highlights and shadows could not be seen unless there was some type of backing on the image. He mixed a combination of banana oils and bronzing powders to create a sepia or a goldtone effect, and then spread this mixture onto the dried emulsion.
 Icom cc.icom.museum/ Documents/ Working Group/ Photographic/ Newsletter - 01-2006.pdf