Step 1 of the process
Coarse grind
The only step that changes the shape. Run it again and again until every stone is rounded and free of pits, because nothing later can fix shape.
- Goes in the barrel
- coarse grit, 60/90 silicon carbide
- Typical run, rotary
- 7 days per run, repeat until shaped
Step 1 does the heavy work. Coarse 60/90 silicon carbide grinds off corners, pits and broken faces and gives each stone its final shape. Every later step only smooths the surface this one leaves.
A run lasts about 7 days in a rotary tumbler. By then the grit has broken down into mud and stopped cutting. Open the barrel, rinse the stones and look at them. Hard, jagged rough rarely finishes in one week: two to four runs with fresh grit is normal, and stones that started out rounded may need only one.
Take out the stones that are done and keep running the rest, topping the barrel up with new rough or ceramic media so it stays at the fill line.
Ready to move on when: Every stone is rounded, with no pits, cracks or flat broken faces. If you can catch a fingernail in a flaw, it goes back in.
Common mistakes at this stage
- Moving on after one week because the calendar says so.
- Carrying a few unfinished stones forward: they scratch the whole batch later.
Notes for this stage
- Rock tumbling grit chart: grit size, amount and time for each stageRock tumbling grit chart for all four steps: grit size, what each step does, days per step and how to tell it is done, plus about 2 tbsp of grit per pound.Chart
- How to tumble rocks: a step-by-step guide for beginnersHow to tumble rocks in a rotary tumbler: load the barrel 2/3 full, run four grit steps of about 7 days each and clean between them. 4 to 6 weeks in total.How-to
- How long to tumble rocks: time for each stage and the full runHow long rock tumbling takes: about 7 days per stage and 4 to 6 weeks for a full batch, with times by rock type and the signs that a stage is finished.How-to