Part of the process
Rough rock
Pick rock that is hard enough to take a polish and keep each load to one hardness. Agate, jasper and quartz are the easy ones; softer or brittle stones need their own load and a gentler schedule.
The rock decides the result more than the machine does. The best tumbling material sits around Mohs 7: agate, jasper, quartz and petrified wood. These are hard, tough and take a glassy polish with the standard four steps.
What matters most is that everything in one barrel has about the same hardness. Put a soft stone in with hard ones and the hard ones grind it away. Rock with pits, cracks or a grainy, crumbly texture will not polish no matter how long it runs, so sort it out before you start.
A good load mixes sizes, from pea-sized pieces up to stones about half the width of the barrel. Small pieces carry grit into the gaps and keep the load rolling.
Common mistakes at this stage
- Mixing hard and soft rock in one load.
- Tumbling cracked or porous stones that trap grit and carry it into the polish step.
- Loading only large stones, so they slide and chip instead of rolling.
Notes for this stage
- Rock tumbling quartz: grit schedule and how to avoid chipped edgesQuartz tumbling recipe: grit and time for each step, how much ceramic media stops chipped and frosted edges, and how quartzite differs.How-to
- Rock tumbling Petoskey stones and other soft rocksPetoskey stone is calcite, about Mohs 3, too soft for the standard recipe. Hand sanding with 220 to 600 grit is usual. A short tumbler schedule if you tumble.How-to
- Rock tumbling obsidian: cushioning, grit and timingObsidian is brittle volcanic glass at Mohs 5 to 5.5. Gentle schedule: barrel 2/3 to 3/4 full, 30 to 50% media, short coarse run, no white bruises.How-to
- Rock tumbling agates: grit, times and common problemsAgate tumbling schedule start to finish: grit and amount for each step, 5 to 8 weeks in total, plus fixes for pits, fractures and dull bands.How-to
- Best rocks for tumbling: hardness chart and rocks to avoidHardness chart for 20 common tumbling rocks: Mohs value, whether each one polishes, which rocks can share a barrel and which to skip.Chart
- How to make sea glass in a rock tumbler: grit, amounts and timingMake frosted sea glass in a rock tumbler: barrel 2/3 full, 2 tablespoons of coarse grit per pound, 3 to 7 days, no polish step. Recipe table and safety.How-to
- How to find rocks to tumble: where to look and what to pick upWhere to find rocks to tumble for free, plus the scratch and rub tests that show in a minute whether a beach, river or yard rock will polish.How-to