nik
spending too much on rocks
Member since May 2019
Posts: 315
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Post by nik on Jan 10, 2020 7:25:02 GMT -5
I have run up against a problem with undercutting on some of the boulder opal that I've been working lately. There have been a few cabs that have polished well with epoxy and acetone stabilization, but I would rather just find a way to polish untreated stones.
After doing a bit of homework, thoughts have turned toward making a handful of phenolic wheels. The idea is rooted in things like the grooved star laps and spool polishers which are charged with diamond compound, but in 6" wheel format
I never seem to have any issue with undercutting until the stones are on the final polish, so I'm thinking just 14,000 and 50,000 to start. The material is cheap enough that making another set for other grits or contours is feasible as well.
If anyone has any tips or thoughts on this idea or using spool polishers, I'd love to hear it.
Thanks in advance.
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Post by hummingbirdstones on Jan 10, 2020 8:18:29 GMT -5
Can you post a picture of one the opals that is undercutting? I don't recall ever having this problem with boulder.
There are always those pieces where the ironstone is not the nice dark, hard type, but has the mustard color softer material that does not polish because it is so soft and there's really not much you can do with that except maybe stablilize it. The natural voids where opal has fallen out of the "seams" is also something you really can't get away from and you can fill those voids with epoxy, although I usually leave them. That's how Ma Nature made them.
If you don't have an 8,000 grit wheel, you may want to try that instead of the 14k. For some reason boulder likes the 8k better.
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nik
spending too much on rocks
Member since May 2019
Posts: 315
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Post by nik on Jan 10, 2020 17:18:30 GMT -5
 IMG_20200111_075947 by nik1924, on Flickr This one has not been treated, the matrix takes a decent polish, but is undercut more than I'd like.  IMG_20200111_080117 by nik1924, on Flickr A lump of the rough. I believe that it is matrix opal from Opalton. There is a bit of porosity in the matrix, but it does not seem to pick up the polishing compounds that I have used.  IMG_20200111_081024 by nik1924, on Flickr These two have been treated with 330 epoxy thinned with acetone, and came out pretty well, but I just don't like the idea of treating the stones. |
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Post by hummingbirdstones on Jan 10, 2020 21:10:25 GMT -5
Very nice! Are they all Opalton? I don't think I've ever cut any Opalton boulder. Lots of Koroit, Yowah and Jundah, though.
The dark matrix stones in your pictures look fine to me. I can see where you're saying they're undercutting, but I think it may just be the really fine cracks in the ironstone where the opal formed and I'm not sure there's a way to prevent that. gemfeller and opalpyrexia -- any ideas?
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gemfeller
Cave Dweller 
Member since June 2011
Posts: 4,064 
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Post by gemfeller on Jan 10, 2020 23:01:19 GMT -5
It's hard to tell exactly what's happening. With a magnifying glass on my screen it seems the opal's harder than the ironstone in these pieces. I've cut a lot of boulder from various places but usually ironstone of that dark color is a lot harder than the opal. I think the phenolic might be worth a try to keep everything cutting evenly. But boy those disks have gotten expensive! It could be a fairly costly experiment if it doesn't work. Wish I had something better to suggest but I've never run into that problem. Good luck!
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Post by opalpyrexia on Jan 10, 2020 23:06:34 GMT -5
I haven't had experience with it but I found this comment on Ganoksin that might suggest a method. "My mentor in Australia who cuts matrix opal gave me the following "receipt" for cutting it and getting a good polish.
Rough cut it as any other stone. Start the sanding on 400 grit "DRY" Progress through 1200 grit still DRY Now go to an expandable drum with a resin belts and diamond paste starting at 6000 and going through 50,000. Little water in each step and limit the time in each step. Let the diamond do its work to eliminate the under cutting. You can end up with a very good polish and surface using this method."
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Post by opalpyrexia on Jan 10, 2020 23:08:49 GMT -5
Alternatively, feature it. I'm sure that there are potential customers who would like the look.
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nik
spending too much on rocks
Member since May 2019
Posts: 315
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Post by nik on Jan 11, 2020 4:34:20 GMT -5
 IMG_20200110_220137 by nik1924, on Flickr one more of the treated stones, it got a bit too hot against the leather during polishing, and left a couple dark spots around the girdle. I am a bit torn as to weather or not to grind it away because it is one of my favorites from the parcel. the blues and greens are really lively in person. to answer the questions. hummingbirdstones, as far as I know, all of them are from Opalton, it came from one seller in two parcels and one large stone. gemfeller, the plan is to get some 1-2" thick canvas based phenolic sheet and cut the wheels out on a lathe. Material for 4 6" wheels will cost me about $60, including shipping to Guam, then it is just a matter of making a mandrel and turning them on the lathe to whatever size and contour seems right. Phenolic machines pretty well, albeit messy and stinky. opalpyrexia, thanks for the tip. I'll give it a try, as I already have everything needed. As far as finding someone to buy them, in general, I don't sell. Getting a high, glassy polish without treatment is really more to satisfy my own neurosis rather than anything else. |
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Post by opalpyrexia on Jan 11, 2020 11:01:40 GMT -5
That last opal looks really good. I can't see any undercutting. Getting a high, glassy polish without treatment is really more to satisfy my own neurosis rather than anything else. I understand. I think that most of us have more or less neurotic feelings about resorting to treatments. |
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nik
spending too much on rocks
Member since May 2019
Posts: 315
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Post by nik on Jan 16, 2020 6:19:22 GMT -5
 IMG_20200116_182003 by nik1924, on Flickr The wheels are done, they wound up being about 5 3/4" diameter, the fly cutter chattered a bit and they were not quite round. 1" thick. I'll try them out this weekend. |
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