Tumbling coarse 60/90: 7 days vs. 5 days

Thanks for the explanation, LCARS. I think I get it.

If the goal is to increase the density of the liquid mixture in order to suspend the coarse grit for longer, then would it help to add a finer grit to the initial loading? That is, when starting a fresh load of rough rock with coarse grit, add a TB or so of pre-polish or other fine grit in addition to the 4 TB of 60/90? Maybe that would create an instant slurry? Are there other additives that might achieve the same goal, like sugar or some other easily suspended thickener?

Some people have reported success using things like sugar or corn starch trying to pre-thicken the water to promote slurry formation.
BUT, as many have also found out, it is a BAD idea to use anything organic in a tumbler barrel.
Yeast, mold or bacteria present in every day life can feed off sugars, starches & other organic matter, possibly producing nasty or even toxic fermentation products including pesky offgassing which can lead to barrels bursting from pressure build-up.

I (and many others here like me) have had a very good track record using the slurry recycling technique. This involves recovering and storing the slurry you've already produced during previous batches to use to jump start slurry formation in future batches.

During the last 60/90 recharge I make sure to run for an extra two days to get as much of the grit broken down as possible. When it's time to move on to 120/220 I strain out and collect the slurry in a ziploc container before rinsing the stones. I leave it to decant for about 24hrs then gently pour off the water at the top.

Once there is no more water resting at the top you can either throw a lid on it as-is or leave it out to dry completely. Mark the container with what type of stone & grit was used because it's important to use simillar slurry for simillar stones and only in the same stage to prevent cross contamination.

If you decide to dry it out, it's best to crush the resulting "brick" into powder to evenly distribute the varying constituents. If you store it as a liquid, you may find more water will separate over time but you will need it to stir up the slurry to be able to pour it out later on so don't pour it all off.

As I general rule, I add about half of the slurry that I recovered from a previous batch to the next batch to start it off. You don't want to add too much or you could end up with overly soupy slurry before it's done.


If you are new to tumbling and you have yet to run a few batches then you are not likely to have any saved slurry on the shelf but this would be a good time to start your slurry collection.

Borax can be effective at promoting slurry formation, does not promote microbe growth and is generally slated as beneficial to rock tumbling anyway. Adding up to a tablespoon of that 20 Mule Team miracle powder for every 3 pounds of barrel capacity when starting a fresh batch will do ya just fine.