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Post by grumpybill on Apr 26, 2019 11:22:02 GMT -5
I was asked if I could/would polish some Petoskey stones in exchange for being allowed to keep a few “picks of the litter” from the finished stones. The challenge enticed me to give it a go. After a lot of research here and elsewhere, I decided to try a slightly modified version of the formula Jugglerguy posted a few years ago for the first batch. Jugglerguy's threadThe main modification was, hoping to mitigate any undercutting, I chose the smoothest stones and skipped the course grind stage. I started with an abbreviated (about 14 hour) run of 120/220 in my Lot-O. (Wet, of course.) This might have been a mistake, as evidenced by the orange peel surface. Then, after letting them dry overnight, I followed jugglerguy's recipe of 1 Tbls of AO in ground up corncob for 36 - 48 hours in each of the 500, 1000 and polish stages. I bought corn cob pet bedding at Walmart. For less than $6 I got more than twice enough to fill the Lot-O 3 times. Because the corn cob weighs almost nothing and I only put a few stones in the Lot-O, it vibrated hellaciously. Very noisy and the bowl jumped part way out of the machine a couple times. I'm going to load it heavier on the next batch. The corn cob either breaks down or consolidates after a few hours. I needed to add more at least once in each stage to keep the bowl filled. Sorry for the inconsistent color/lighting in the photos... Here are the stones I started with (dry): Wet, before starting: After 120/220, dry: After 500: After 1000: Finished:
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Post by miket on Apr 26, 2019 11:25:49 GMT -5
Very nice!
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Post by MsAli on Apr 26, 2019 12:34:29 GMT -5
Great job on those
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jimaz
spending too much on rocks
Member since July 2018
Posts: 461
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Post by jimaz on Apr 26, 2019 12:43:35 GMT -5
They turned out very nice.
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Post by Jugglerguy on Apr 26, 2019 17:24:05 GMT -5
Those look great! They always come out with some texture using that method. I don’t think the texture looks bad, and I don’t know how you could avoid it. If you really don’t like the texture, use a combination of tumbling and hand polishing. You could also do them on a cab machine or flat lap after tumbling. If I was going to hand polish, I’d only run them through 220 or 500 before going to sandpaper.
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braat
spending too much on rocks
Member since December 2016
Posts: 350
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Post by braat on Apr 26, 2019 21:22:57 GMT -5
Thanks for sharing the video...I've often wondered how to hand polish rocks... I think I'll have a go at a couple that didn't turn out in the tumblers...
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Post by hummingbirdstones on Apr 26, 2019 22:12:28 GMT -5
I think you did a helluva job those. They look great!
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Post by grumpybill on Apr 27, 2019 6:40:55 GMT -5
Thanks for the compliments, everyone. Most of the credit goes to Jugglerguy and his thread on using corncob in a Lot-O. I still have 5 or lbs. of petoskeys to polish. Some will need tumbled in course abrasive or hit with a flex tool. I'll probably experiment with each batch, trying different things. I'll update this thread with anything that works and/or doesn't work. I doubt I'll spend the time hand polishing them...except, maybe, the ones I get to keep for myself. Hmm...I have a grandson who liked playing with sandpaper when he was 5 or 6......
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Post by fernwood on Apr 27, 2019 6:50:04 GMT -5
They look great to me.
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lancemountain
starting to spend too much on rocks
Member since March 2017
Posts: 214
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Post by lancemountain on Apr 27, 2019 9:06:52 GMT -5
Fantastic!
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Post by Rockindad on Apr 27, 2019 15:02:28 GMT -5
Thanks for the compliments, everyone. Most of the credit goes to Jugglerguy and his thread on using corncob in a Lot-O. I still have 5 or lbs. of petoskeys to polish. Some will need tumbled in course abrasive or hit with a flex tool. I'll probably experiment with each batch, trying different things. I'll update this thread with anything that works and/or doesn't work. I doubt I'll spend the time hand polishing them...except, maybe, the ones I get to keep for myself. Hmm... I have a grandson who liked playing with sandpaper when he was 5 or 6......Nothing like a little cheap labor Al
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Post by grumpybill on May 7, 2019 12:11:01 GMT -5
I made a few changes during the 2nd batch. 1. I weighed the finished stones from the 1st batch...a little over 11 ounces. I put ~1lb. in the 2nd batch. This made the Lot-O run a lot quieter/smoother. Didn't sound like it was beating itself to death. I didn't notice any difference in the finished product. 2. I ran the 120/220 stage quite a bit longer and went heavier on the 120 and lighter on the 220. I was hoping to get less of the "orange peel" texture. Again, I didn't notice any difference in the outcome. 3. One of the stones had a broken edge. It rounded off pretty well, so maybe I won't need to run the other broken stones through course grit in a rotary.
A future experiment will be to add a handful of pre-polished pea sized agate pebbles to the corncob during the last stage. Thinking I might get some burnishing action from the pebbles. Or...it might beat the Petoskeys all to hell.
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Post by grumpybill on May 8, 2019 7:20:28 GMT -5
Yesterday I delivered the 1st two batches to the people who asked me to try polishing them. I mentioned that some Petoskey fluoresce under UV. When we checked them, EVERY one had at least a few small areas that lit up with a deep burgundy/maroon! (Not sure what wavelength the UV light was.)
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Post by grumpybill on May 14, 2019 8:03:21 GMT -5
I finished and delivered the 3rd batch yesterday. Here are a few observations after that run:
1. Apparently I didn't dry the bowl well enough after the 120/220 cleanout. After the 500 run there was a yellowish coating on the inside of the bowl that was difficult to clean off.
2. For the 2nd batch I added an additional Tbsp. of AO to the recycled corn cob. This time I only added a tsp. and got good results after only 24 hrs. in each stage. I think I can get by without adding additional AO in future runs.
3. A few of the stones in this batch had small pits. Ain't doing that again! The corn cob packed tightly into the pits and was difficult and time consuming to remove at each cleanout. The reaming Petoskys will get some cutting and/or grinding to remove any pits.
4. One of the stones in this batch was almost entirely limestone(?) matrix. It got a fairly decent shine, so I might cut some of my softer material (calcite, rhyolite, etc.) and try using this method with it.
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