Ancient Gold Coins (AN524)

A series of French gold coins minted in 1786 bore Louis XVI's effigy with a notorious additional feature-each seems to include one, sometimes two, "horns" upon the king's forehead. (Figure 1). A controversy has persisted as to whether the horns originated from accidental stamping damage, or whether the minting die had been altered intentionally as a slander against the king.

A study was recently undertaken using non-contact, optical profiling to characterize the topography of several surviving coins3. It was set out to determine, a) whether the two types of coins were minted on the same die, b) whether one version represented the "worn" version of the other, and c) whether any clues were present that could indicate whether the horns were created accidentally or with intention.

Characterization of these coins had hitherto been accomplished through visual inspection at low magnifications (<20X). The results were limited by the subjectivity of the inspector, as well as the degree of wear of individual coins. Scanning electron microscopy (SEM) has given better assessment of surface features; however, the technique does not provide quantitative height data which would more absolutely characterize the samples. SEM also requires careful cleaning prior to measurement to remove surface contamination, a process that can adversely affect sample coins.