There used to be a scam known as "sweating" where the scammer would take a bunch of gold or silver coins, put them in a bag, and shake the crap out of it for a

There used to be a scam known as "sweating" where the scammer would take a bunch of gold or silver coins, put them in a bag, and shake the crap out of it for a while. Small particles of precious metal would wear off and accumulate in the bottom of the bag, which could then be recovered and sold as bullion. Afterward the (now somewhat-worn) coins could still be spent at their original face value. This was hard to detect compared to other common scams of the time(such as clipping or filing the edges of the coin) because the wear pattern was pretty close to what you'd expect from normal wear and tear.