Book 27, Question 96
How does a rock tumbler make stones shiny?
A rock tumbler is a rotating barrel filled with rough stones, water, and gritty powder.
As the barrel turns for days or weeks, the stones rub against the grit and each other, wearing off rough spots. Coarse grit comes first, then finer grits, and finally a polishing powder. The stones come out smooth and shiny. It is noisy, so it's best to run it in a garage.