"In a Mellow Tone" - Duke Elligton - ... anybody know what style that was ? ...

Pumice Stone:
It is also used as an abrasive, especially in polishes, pencil erasers, cosmetic exfoliants, and the production of stone-washed jeans. "Pumice stones" are often used in beauty salons during the pedicure process to remove dry and excess skin from the bottom of the foot as well as calluses.

So basically, it takes your skin off and the ink comes off with it ...