Untersberg

The Untersberg marble ball mill in Bavaria was built in 1683. The marbles once popular primarily as children's toys, were sent all over the world. Via Rotterdam and London,  mainly to the East and West Indies, around 600 to 800 and sometimes even 1000 hundred weight a year. (One hundred-weight contains about 10 000 pieces) They were welcomed by sailing ships, as their high density made them suitable as ballast. Eventually the balls themselves became a cargo and were sold at their destination allowing the ships to carry more cargo back to their home port. Some larger ones were used as cannon balls.

Ball-7B&W
Ball-1a Ball-6
Ball-4

It was a fairly simple manufacturing method that had been developed for the balls. Lumps of marble were hammered into squares with rounded edges and corners then put on stone plates with concentric grooves; then a wooden plate was put on top and run as a water wheel, until, after one: two or three days, the squares had become balls.