In the nineteenth century, before the mint started issuing coins with reeding or grooves on the edges to prevent it, some slightly dishonest people would shave the precious metal just enough to go visually undetected.
They would then have full value for the coin as well as that of the shavings.
If suspicious, a merchant would bounce the coin on a hard surface to hear if it “rang true,” thereby proving its authenticity.
The word ring is from the Anglo-Saxon hringan.
