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Rock tumbling before and after looks like a magic trick: a dull, chalky lump goes in, and a glossy, rounded, color-saturated stone comes out four to six weeks later. In between, each stage does one specific job. Coarse grit rounds the stone, medium smooths it to an even matte, pre-polish adds a faint sheen, and polish brings out the glassy shine.
Expect the stones to shrink, too. Rocktumbler.com says coarse grit removes roughly 10% to 30% of the rock's volume. This guide shows what changes at each stage, how results differ by stone, and why some "afters" disappoint.
One agate, stage by stage
Rough (before)StartAngular or weathered, dull and often chalky. A weathering rind can be 1/8 to 1/4 inch thick. After coarse7 to 10 days, often repeatedRounded with no sharp edges or pits, in a uniform frosted matte. Colors look washed out. After mediumAbout 7 daysAn even, smooth matte all over, like pale river pebbles. After pre-polishAbout 7 daysA faint sheen when dry and a silky feel. After polish5 to 7 daysGlassy shine and full color, the same wet and dry. Smaller than the rough.
Dry view. Switch to wet: water fills the fine scratches and previews the final color, but only the polished stone looks the same both ways.
Illustration, not a photo. Stage descriptions: Kingsley North rotary instructions (including the wet-and-dry test) and Rocktumbler.com, which says coarse grit removes roughly 10% to 30% of a rock's volume. Times are for stones around Mohs 7.
What Changes at Each Stage
| Stage | Grit | What you'll see after | Typical time for Mohs 7 stones |
|---|---|---|---|
| Rough (before) | None | Angular or weathered, dull, often chalky | n/a |
| 1. Coarse | 60/90 silicon carbide | Rounded, no sharp edges or pits; rough frosted matte | 7 to 10 days, often repeated |
| 2. Medium | 120/220 or 150/220 | Even, smooth matte all over | About 7 days |
| 3. Pre-polish | 500 to 600 | Faint sheen when dry; silky feel | About 7 days |
| 4. Polish | Aluminum oxide, cerium oxide or tin oxide | Glassy shine that looks the same wet and dry | 5 to 7 days |
| 5. Burnish (optional) | Powdered soap | Slightly brighter, clean surface | At least 4 days |
Stage times come from Kingsley North's rotary instructions and Harbor Freight's manual for its 6 lb dual-drum tumbler; Lortone's manuals give 5 to 7 days per stage. Our step-by-step rock tumbling guide explains each stage.
Before: Rough Rock
Rough looks unpromising. Weathered beach and stream stones carry a weathering rind, typically 1/8 to 1/4 inch thick according to Rocktumbler.com, plus tiny impact bruises. Broken rough is sharp-edged and scratched. Most sellers photograph rough wet, which hints at the final color; several rough listings say so on the page.
After Coarse: Shape, Not Shine
This is the stage that changes the stone most, and it looks the least impressive. Edges round off, pits and rind disappear, and the surface turns a uniform frosted matte. Colors look washed out.
Don't move on until every stone is rounded and free of pits. Kingsley North calls coarse the most important step and says to repeat it with fresh grit if stones aren't evenly rounded. Rocktumbler.com says its own team usually runs coarse for at least two weeks.
After Medium: Even Matte
Medium grit erases the coarse scratches. Kingsley North's day-7 check is an even, smooth matte finish all over. Stones look like smooth, pale river pebbles.
After Pre-Polish: The First Sheen
Pre-polish removes the fine scratches. Dry stones show a faint sheen and feel silky. This is the last chance to catch contamination, so clean everything very thoroughly.
After Polish: The Real "After"
The polish stage brings back the color and pattern, now behind a glassy surface. Kingsley North's rule is the one to trust: a finished stone looks the same wet and dry. If it only shines wet, go back to pre-polish.
Before and After by Stone Type
Results vary a lot by material. These examples come from Rocktumbler.com's before-and-after page and its tumbling guides.
Agate and Jasper (Mohs 7)
The classic transformation. Rocktumbler.com describes unpolished Lake Superior agate nodules becoming "super-bright" after polishing, with banding visible. Jasper is its top beginner recommendation because it's so durable. Expect a bright, even polish and strong color.
Mookaite (Mohs 7)
Dull rough, vivid polish. Rocktumbler.com ran mookaite 14 days in coarse, then 7 days each in medium, fine and TXP polish in a Thumler's A-R2, and moved much of the later work to a vibratory tumbler because mookaite is brittle and chips in a rotary.
Quartzite and Basalt Cobbles
Big "gnarly" cobbles turn into smooth, satiny stones. Rocktumbler.com ran basalt about three weeks in coarse in a Thumler's Model B before finishing in a vibratory, and quartzite about two weeks in coarse with a grit change after one week. It also had to cull heavily: from a 40 lb bag of basalt, it kept fewer than half.
Leopard Skin and Mixed-Mineral Rock
A softer "after." Rocktumbler.com says leopard skin polishes to a soft glow rather than a bright luster, because its harder minerals stand out in slight relief as the softer ones wear faster. That's typical of any rock made of minerals with different hardness.
Obsidian and Apache Tears (Mohs 5 to 6)
Spectacular when it works, but fragile. Rocktumbler.com says Apache tears are brittle and need slow tumbling and ceramic media to reach a bright polish. Its obsidian recipe skips coarse grit entirely.
Glass
Tumbled glass can end frosted, like beach glass, or glossy. Our guide to making sea glass in a rock tumbler covers both.
How Hardness Changes the Before-and-After
Hardness decides how much a stone shrinks and how long each "after" takes. The manufacturer schedules from Lortone, Harbor Freight and Kingsley North assume stones around Mohs 7. For softer stones, Rocktumbler.com suggests about 1-1/2 fewer coarse days per Mohs point below 7.
| Hardness | Example | What changes in the "after" |
|---|---|---|
| 7 | Agate, jasper, petrified wood | Bright polish; modest size loss on the standard schedule |
| 6 to 7 | Unakite, labradorite | Good polish; feldspars may show cleavage chips |
| 5 to 6 | Sodalite, obsidian | Big size loss if coarse runs too long; bruises without cushioning |
| Below 5 | Calcite, fluorite, marble | Shrinks fast; often a satin rather than glassy finish |
Rocktumbler.com's example of marble shows how different soft stones are: a couple of days of shaping, a day each of fine grits, and a dry polish. Our rock tumbling timeline calculator adjusts stage times for your stone, and our guide to the best rocks for tumbling lists stones by hardness.
How Much Size Do Stones Lose?
More than most beginners expect. In Rocktumbler.com's test with Ohio River stones of 1 to 1-1/4 inches, the stones lost about 1/8 inch around, roughly 25% of their diameter but about 40% of their weight. Basalt cobbles lost at least 3/4 inch of diameter in extra-coarse grit.
Two practical consequences:
- Start with bigger rough than you want to end with. A 1 inch finished stone needs more than 1 inch of rough.
- Top up the barrel. As stones shrink, the barrel drops below the recommended fill. Lortone recommends half to two-thirds full; add ceramic media to make up the volume.
How to Photograph Your Own Before and After
Good comparison photos are half the fun of the hobby.
- Photograph the rough dry, and once wet. Dry shows the real starting point; wet previews the result.
- Use the same background, light and angle for every stage. A gray card or plain towel works.
- Shoot after every stage, not just the end. The coarse-stage photo is the one that teaches you the most.
- Photograph finished stones dry. If they only look good wet, they aren't finished.
- Keep a log. Note the stone, grit, days and fill level for each stage. Rocktumbler.com offers a printable tumbling log.
When the "After" Disappoints
Most dull or pitted results trace back to a few causes:
- Coarse cut short. Pits and rind survive into later stages. Go back to coarse.
- Contamination. One coarse grain in the polish leaves scratches. Clean the barrel, lid and stones thoroughly between stages.
- Underfilled barrel. Rocktumbler.com says below about half full, stones are violently tossed around and chip or bruise.
- Overfilled barrel. Above about 2/3 to 3/4 full, there's no room to tumble, and Rocktumbler.com says rocks barely change in a week.
- Mixed hardness. Soft stones come out small and pitted.
- The wrong rock. Porous, fractured or grainy rock never polishes. Rocktumbler.com says most rock types don't perform well in a tumbler.
Our upcoming rock tumbler troubleshooting guide covers each problem in detail. To start with rock that's likely to give a great "after," see our rough stones for tumbling picks.
What to Do With the Results
Once your stones pass the wet-and-dry test, sort them: keepers, gifts and stones that go back for another round. Our guide to tumbled stones covers identification and uses, from display jars to jewelry.
FAQ
How much smaller do rocks get after tumbling?
Noticeably. Rocktumbler.com says coarse grit removes roughly 10% to 30% of the rock's volume. In one batch of 1 to 1-1/4 inch river stones, it reported a loss of about 1/8 inch around, roughly 25% of the diameter but about 40% of the weight.
Why do my rocks look better wet than after tumbling?
Water fills the tiny scratches on a rough or matte surface, so wet rock previews the polished look. If a tumbled stone only shines when wet, it's not finished. Kingsley North's test is that a fully polished stone looks the same wet and dry; go back to pre-polish if it doesn't.
What do rocks look like after the first stage?
Rounded and dull. After coarse grit, stones should have no sharp edges, pits or deep cracks, but the surface is a rough, frosted matte. That's normal. The color and pattern only show strongly again after the polish stage.
Do all rocks get shiny in a tumbler?
No. Hard, dense stones such as agate, jasper and petrified wood take a bright polish. Some materials, like leopard skin rock, take only a soft glow because their minerals vary in hardness, and porous or grainy rock may never polish. Rocktumbler.com says most rock types don't perform well in a tumbler.