Mahogany Finish. A deep, dark patina finish which ranges from chocolate brown to red-brown. (The color closely resembles that of mahogany wood, hence the name). It was extensively used by the United States Mint on all its bronze medals in the later half of the 19th century but was phased out (beginning 1900 and ceased by 1910) because it was so labor intensive and time consuming. It was accomplished by a double-heating process known as fire-bronzing. (It is said one could have ordered medals from the Mint in either the dark mahogany or the lighter patina finish during the 10-year transition period at the buyer’s option.)

Fire-bronzing predated the highlight-by-oxidizing-and-relieving finishing process, developed by the French in the 1880s, which the U.S. Mint adopted in place of fire-bronzing. (Numismatists called this later finish yellow-bronze). A close approximation of the mahogany color was achieved in 1930 by the Medallic Art Company for the Second Issue of the Society of Medalists, Dionysus, by Paul Manship. It accomplished this dark brown bronze patina with chemicals (ferric nitrate) but this was still not the exact deep mahogany color that results from red lead and fire-bronzing used in the 19th century.

In addition to fire-bronze, fire-bronzing, see also patina, finish and finishing.

Reference:

M37 {1977} Julian, Introduction, p XXXV-XXXVII (35-37).