A very early and rare example of the Heliographic process of Henri Garnier. The four plates, Pl VIII-XI are from photographs of coins from the book:Roswag, C. Metaux precieux consideres au point de vue economique : ouvrage orne de 28 gravures dans le texte, de 16 planches coloriees, et d’une carte (Babinet) de la production, de la circulation, et de l’absorption des metaux precieux Garnier, Henrie Imprimerie Delatre (Paris, France)
Henri Garnier and Alphonse Salmon developed a dusting-on process using iron citrate. The process depended on iron citrate becoming non-hygroscopic when acted on by light and on the adhesion of carbon powder to moistened iron citrate unmodified by light. A very strong solution of iron citrate was coated on a sheet of paper, placed under a positive print and exposed to light. On removal from the printing frame the paper was dabbed with carbon powder at the same time as breathing on it, the carbon powder would attach itself to the unexposed parts. Dipping in water would remove the unaffected citrate of iron.
Hanson, David Checklist of photomechanical processes and printing 1825-1910, 2017 p. 56
Bridson/ Wakeman (pg. 168, E94)