I happened across a note on the web that recommended recycling the polish used in rock tumbling. The author felt that it didn't wear out (as the grinding grits do) and that this was a place where one could save some money. I use aluminum oxide, right now, and it is not too expensive - but, cerium oxide is rather pricey and others are even higher.
So, I set out to do an experiment - to capture the polish after a polishing cycle, to see how quickly it would settle out, and then see if it would indeed work for subsequent loads.
I started with the polish drained from my 15 pound, Thumler Model B tumbler. So this is just under a pound of aluminum oxide in whatever amount of water was in the barrel and was used to rinse the rocks.
The following sequence of photos documents the settling. The first picture is at 3 minutes - the time it took me to fetch the camera after deciding to do this. Settling started quickly and the water above the sediment is surprisingly clear.
Aluminum Oxide Settling - After 3 minutes
Aluminum Oxide Settling - After 15 minutes
After 25 minutes, I poured off the water and combined the sediment from both pitchers into one.
Aluminum Oxide Settling - After 25 minutes
Aluminum Oxide Settling - After 2 hours
Aluminum Oxide Settling - After 2 days
The settling continues after 2 days. This last bottle is actually full to the brim - the seperated water continues to be really clear.
Quite a consolidation. And the sediment is beginning to get "sticky" - acting almost like a putty. This is why every webpage you read on how to tumble rocks warns that you - never - pour the residual grit or polish down a drain. As you can see from this sequence of pictures, this stuff settles out quickly, very quickly. As it settles, the density of the sediment bed goes way up, so no amount of water will wash it out of your plumbing.
Here are a couple of movies. The first is 1000 mesh aluminum oxide grit (about 12 ounces) in 2 quarts of water. It settles out over 1 hour. The movie captures a frame every 2 seconds and runs for 2 minutes. The second movie is aluminum oxide polish (even finer than 1000 grit, in fact, much like what is used in tooth paste). About the same amount of polish in the same amount of water and it really settles out quickly.
I encourage everyone to get a tumbler and polish some rocks - but, do not pour any of the polishing residue down the drains in your house.
