Collected Information on Rock Tumbling
Quick Start (Rotary Tumbling)
Last update (this page): March 16, 2008
If you just obtained a rotary (not vibratory) tumbler and want to get
started as fast as possible, read this section and go play.
Fill the barrel 2/3 to 3/4 full of rocks. All the rocks should
be small enough to tumble without getting wedged in the barrel. For
best immediate gratification use hard, solid, silicified rocks like
agate or jasper (including most fossil wood), and don't mix in softer
rocks like calcite, quartz (hard material but it "frosts"), or feldspar.
Add coarse silicon carbide grit (described such as "30", "60/90",
etc, for the grain size).
I use 4 tablespoons (volume) for a 3-pound Lortone barrel, and 8 ounces
(1 cup) for a 12-pound Lortone barrel.
Add water, enough to nearly cover the rocks.
Ensure the lip on the barrel is clean.
Seal the lid per the manufacturer's directions and start
tumbling. Ensure the lid is on tightly and evenly. Wait one week.
Keep an ear on the tumbler occasionally and glance at it once or twice a
day. If you are away from home for more than a day, turn off the
tumbler while you're gone and resume when you get back. (I keep paper
handy to log the start date, etc.)
Rock tumbling makes a little noise. Put the tumbler
where the noise is hidden or at least muffled to a nice waterfall sound
you can enjoy rather than hate. Also pick a place that's not cold
enough to freeze the contents of the barrel, as cool as possible to be
nice to the motor, not too dusty, dirty, or wet, and safe from bugs,
kids, and pets.
If you underfill the barrel it sounds noisier. If you
overfill it, it makes a lot less noise and the tumbling doesn't
work well. You'll figure this out pretty fast with experience.
Many instruction manuals say to check the rocks more frequently
than weekly. This is messy and really unnecessary. My experiments say
only a trace of coarse grit remains after 5-6 days, and none after 7
Many instruction manuals say to burp the barrel periodically.
This is also unnecessary, the only exception in my experience being
bottle glass, it does "outgas" and expand the barrel. All other
materials I have ever tumbled seem to dissolve some of the gas, rock, or
grit, such that the barrel ends actually suck in during the week. Just
keep an eye on the bottom end of the barrel for bulging out (bad) or
sucking in (not a problem).
Timing is not critical with rotary tumblers. You can mess with
them a day early, or let them run several days late if you get too busy
to mess with them.
Open barrel, wash thoroughly: Lid, barrel, rocks. Do
not pour the slurry down the drain, it will clog your pipes. The
simplest method is to catch it in a bucket (ask for free "bakery
buckets" at a supermarket), let it settle, and pour off the nearly clear
water. Gather dense slurry until you have enough, set it aside to dry
thoroughly, and trash the resulting "mud brick".
I scrub the edge of the lid and the lip of the barrel with an old
toothbrush. I also make sure to get all the slurry and grit out of
holes and crevices in the rocks when going to a finer grit.
Study the rocks.
Are they smooth enough to make you happy? If not, repeat another week
with coarse grit. Otherwise go on to fine grit. It can take 1-4 weeks
of coarse grinding depending on how smooth your rocks are to start with
and how rounded you want them to be when polished. (I like my rocks
Note, I have enough rocks in the process that every time I dump the
barrel from a coarse load, I sort the rocks into at least three classes:
Ready to polish.
Needs more coarse grinding.
Junk, throw it away.
But especially if you are tumbling all identical rocks it's fine to
never sort them, and just repeat coarse grinding the whole load one week
at a time until you think they're mostly ready to polish. In this case,
start with the barrel kind of over-full because the rocks "shrink",
mostly during coarse grinding, and you need enough to work well in the
When you have a "full" load of rocks ready to polish, run them a week
with fine silicon carbide grit (like "220"). Then run them a week with
"pre-polish compound" (a coarse metal oxide powder), and finally a week
with "polish compound". For the latter I prefer cerium oxide, but tin
oxide is good too. I find alumina (aluminum oxide) doesn't work well.
Note well, you must dump the slurry from the coarse and fine runs, but
you can reuse -- a lot -- the more expensive prepolish and polish
How'd it go?
If you wash and dry rocks from the final polish step and they are not
shiny enough to please you, there are several possibilities:
Wrong kind of rocks.
Some rocks are just too soft or irregular, or tend to end up "frosted".
It's still fun to experiment. If at least one of your rocks in a load
is nice and shiny while others are not, probably the others won't take a
shine, or at least need
Need more polish time.
Try running them several more days, or even another week, with polish
compound. Another trick I use is to just get "lazy" and let the polish
runs go a bit long on purpose, like 8-9 days.
Are you sure you got the rocks and the barrel and lid totally clean
between steps? Traces of coarser grit can mess you up.
Sometimes a crack in a rock will break apart late in the game, and the
new, rough edges mess up other rocks in the load. This is disappointing
but easy to fix with more tumbling time.
Remember to lubricate (oil) your tumbler as the manufacturer
recommends. On my 3-pound unit I oil the shafts once a month with 10W30
motor oil from an eye dropper bottle, and the motor only rarely when it
On my 12-pound unit I oil the shafts about every two weeks and the motor
about every three months.