Fire-bronzed, Fire-bronzing. A finishing technique requiring a double heating process to patina a medal. The process was used before the French antiquing or oxidizing and relieving method was developed. Fire-bronzing was in use in the early 19th century to the beginning of the 20th century. It is noted for being a physical patina application rather than a chemical one, it particularly does not employ abrasive blasting to prepare the surface for treating with a liquid. It was employed by both private and national mints in many countries.

Fire-bronzing process. The following procedure produces a chocolate brown to

red-brown color on bronze medals – numismatists called this mahogany finish. It was used by medallic firms in Philadelphia in the late 19th century. The medal must first be cleaned of all impurities (by degreasing), then placed in an oven and heated. It is then picked out with a pair of tongs, immersed into pure cotton seed oil, picked out of the oil and dropped into a bed of powdered red lead (lead tetroxide). It emerged looking like a powdery cookie with the powdered red lead covering its surface. It is then placed in the oven a second time, heated and removed. If the oil and red lead uniformly covered the surface, the resulting color would be uniform; if the color was not uniform – spotty, blotched or unattractive – the procedure could be repeated.

Reference:

037 {1977} Julian, p XXXV-XXXVII.