Ancient people noticed smooth surfaces of river rocks and learned to replicate the process that polished them. Here’s a bit of history about rock tumbling.
Top 10 Rock Tumblers
NSI The Original Electric Rock Tumbler
Hobby Rock Tumbler – National Geographic
A Brief History of Rock Tumblers.docx - A Brief History of Rock
Your Complete Guide to Rock Tumbling - Step-by-Step Instructions
History of Rock Tumbling - Gold Prospecting Mining Equipment
65T Rotary Tumbler – Diamond Pacific Tools
25RT Rotary Tumbler – Diamond Pacific Tools
Your Complete Guide to Rock Tumbling - Step-by-Step Instructions