Trade beads, or slave beads, were decorative glass beads made and used between the 16th and 20th century as currency in exchange for goods, services and slaves (hence the name). They were made in Venice and Bohemia for European explorers, and then traders across Africa.  These became so popular that countless tons of these beads were used as ballast in slave/trade ships for the outbound trip. Human cargo and ivory, gold and other goods filled the return trips.  Good specimens are increasingly more difficult to find, as they are no longer produced in such quantity.  Mine have travelled across continents and traded in many hands for more than a century, so dings and chips are part of their story.

I lived in Venice for a while, working with these beads in the shop of a Venetian collector, where I had access to these antique beauties. I even found some on the (private) beaches near the furnaces on Murano where modern beads are made.

https://en.wikipedia.org/wiki/Trade_beads