Tumbling Petoskey Stones - Kona update Pg. 6
Aug 29, 2015 14:27:47 GMT -5
gingerkid, mibeachrocks, and 4 more like this
Post by Jugglerguy on Aug 29, 2015 14:27:47 GMT -5
I'm on a quest to tumble Petoskey stones, which is probably a waste of time, since everything I've ever read says that it can't be done. Petoskey stones are made of limestone, so they're about four on the Mohs scale.
Tumbling in a rotary with coarse grit is no problem at all. I just add extra water because they grind down so fast that the slurry gets really thick, like pudding. I use one tablespoon of 80 grit for a six pound barrel. Tumble them for about three days before checking them.
The first thing I tried was my Lot-O after coarse grinding. I did 120, 500, and 1000 grit for about 6 hours each. They started going bad in 500 grit, although it was much more noticeable in 1000 grit. They start undercutting and getting tiny holes in them. This was a pretty bad failure.
My second attempt was using mibeachrocks method, but without the mineral oil. I sort of feel like mineral oil is cheating (sorry Jason). After rough tumbling, I ran them in the rotary with 220 SC and plastic pellets for 2.5 days. Then I ran them for four days with 500 AO and plastic pellets. They came out looking good, but with a very slight texture. I could barely feel the polyps of the coral. This wasn't a bad thing, just different than doing them on a flat lap. At this point, I polished one rock with Zam on a flat Dremel wheel and it got fairly shiny. It wasn't as shiny as doing them on a flat lap, but it wasn't too bad at all. Recently I had great luck polishing a Petoskey by hand. I did the polish step using AO polish on denim. So I thought I'd try this method in a tumbler. I cut up some old jeans into approximately 1.5x1. inch squares. I soaked them in water and squeeze out the extra water. Then I layered denim, polish, and Petoskeys in the barrel like making lasagna. I ran them for three hours before checking them. The barrel was almost filled to the top when I started, but when I opened it, the denim had all stuck to the sides of the barrel and the rocks were banging around inside. They were bruised enough that I put them back in 120 grit for a couple days before I try something new. That's where they are now.
Steve Hart claims to have tumbled them through 1000 without a problem on his website. I haven't tried his method yet. It's basically the same as Jason's, but he used ceramic pellets instead of plastic.
I'd like to try some sort of dry tumbling. I have some corn cob that I could try in the Lot-O. Can corn cob be used in a rotary? Does anyone have any other ideas I could try?
Tumbling in a rotary with coarse grit is no problem at all. I just add extra water because they grind down so fast that the slurry gets really thick, like pudding. I use one tablespoon of 80 grit for a six pound barrel. Tumble them for about three days before checking them.
The first thing I tried was my Lot-O after coarse grinding. I did 120, 500, and 1000 grit for about 6 hours each. They started going bad in 500 grit, although it was much more noticeable in 1000 grit. They start undercutting and getting tiny holes in them. This was a pretty bad failure.
My second attempt was using mibeachrocks method, but without the mineral oil. I sort of feel like mineral oil is cheating (sorry Jason). After rough tumbling, I ran them in the rotary with 220 SC and plastic pellets for 2.5 days. Then I ran them for four days with 500 AO and plastic pellets. They came out looking good, but with a very slight texture. I could barely feel the polyps of the coral. This wasn't a bad thing, just different than doing them on a flat lap. At this point, I polished one rock with Zam on a flat Dremel wheel and it got fairly shiny. It wasn't as shiny as doing them on a flat lap, but it wasn't too bad at all. Recently I had great luck polishing a Petoskey by hand. I did the polish step using AO polish on denim. So I thought I'd try this method in a tumbler. I cut up some old jeans into approximately 1.5x1. inch squares. I soaked them in water and squeeze out the extra water. Then I layered denim, polish, and Petoskeys in the barrel like making lasagna. I ran them for three hours before checking them. The barrel was almost filled to the top when I started, but when I opened it, the denim had all stuck to the sides of the barrel and the rocks were banging around inside. They were bruised enough that I put them back in 120 grit for a couple days before I try something new. That's where they are now.
Steve Hart claims to have tumbled them through 1000 without a problem on his website. I haven't tried his method yet. It's basically the same as Jason's, but he used ceramic pellets instead of plastic.
I'd like to try some sort of dry tumbling. I have some corn cob that I could try in the Lot-O. Can corn cob be used in a rotary? Does anyone have any other ideas I could try?