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 Post subject: ethiopian welo opal questions
PostPosted: Wed May 29, 2019 3:00 pm 
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ok, I am back. I need help again. I have cut a few stones, and have been using superglue for the initial dop, cutting the pavilion, and then transferring using 5 min epoxy. I've then been placing the stone in acetone and the epoxy seems to be rubbing off clean fairly easily. Now, I've had a little trouble. I had a piece of welo opal that was clear, not super colorful, but I thought it would be neat faceted. I separated the rough into two clean pieces. The first piece I cut without too much trouble, transferred with the epoxy. It came off the dop very quickly in acetone, but I noticed there was some harder residual stuff still stuck to the pavilion. I kept it in there a couple days longer, and I seemed to be able to scrape it off with my fingernail, although it was not as easy as the other (non opal) stones I have cut. Anyway, I noticed under close scrutiny there were still just a few very minute marks that I could not seem to rub off. I figured that these might just be tiny pits I missed polishing or something.

So I cut the other piece I had from the rough, dopping the same way, and now I'm wondering if it was a bad idea to use the epoxy. I've gotten most of the epoxy off the pavilion, just using a plastic knife and soaking in acetone a few days, but I've got several small marks on the pavilion. I don't think they are scratches I missed, and I'm not sure if they are actually pits or residual hard epoxy. Can the epoxy pull out pits from the surface, or is it likely that I am just not getting all the epoxy off? Should I buy some "attack" and try soaking it in that?

Also, I should mention, that I had been using the devcon 5 min epoxy previously, that was only rated to 1500 psi. I could not find that at the hardware store last time, so I used loctite 5 min epoxy, which was rated stronger at like 2500 or 3k psi. I'm not sure if possibly the problem is that I changed brands, or if it is solely to do with the stone being welo opal.

I read somewhere you should use CA on opal, but I was not sure how you dop the pavilion with it. I've tried using the CA gel on the pavilion of another stone, but the stone broke loose very easily and didn't seem to fill the gaps at all. I also read if you put too much glue on the bond is compromised, so I didn't think the solution was to glob a ton on. Is there a way to dop the pavilion with CA that gives a decent bond?

Thanks for you help


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 Post subject: Re: ethiopian welo opal questions
PostPosted: Thu May 30, 2019 7:01 am 
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Location: Cape Town, South Africa
rattlesnakeagate wrote:
Is there a way to dop the pavilion with CA that gives a decent bond?

There are two ways to do this. If the stone is not very heat sensitive, fill the pavilion dop with a low temperature wax, like jeweller's green wax, and let it cool until it is still just plastic and takes a dent from a fingernail. Then push the pavilion into it, in a transfer fixture of course, and pull it out again quickly to make an impression of the pavilion. Then use a small amount of CA in the impression to glue the pavilion to the wax. Using a CA accelerator, like Zip Kicker by ZAP, helps set the glue if it is reluctant. When the CA has set, paint the join with clear nail varnish to protect the CA bond from softening in water.
For very heat sensitive stones, the alternative is to make yourself a set of 'anti-dops' by grinding three large cylindrical dops into a 45* cone, a wedge, and a trigonal pyramid. (I owe this idea to Tom Herbst's Amateur Gemstone Faceting.) Use an appropriate one of these to make the impression in soft wax and when it has cooled you can glue a heat sensitive stone into that impression, preferably using a gap-filling CA and accelerator, followed by the clear nail varnish treatment. Soaking in acetone overnight leaves a clean stone.


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 Post subject: Re: ethiopian welo opal questions
PostPosted: Tue Jun 04, 2019 11:30 am 
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Thanks Duncan, I have heard of the first technique but did not know you could use the green wax.

In the second technique, what is the advantage of having the wax impression if it does not closely form fit the stone? It would seem like the contact would be nearly the same with just a bare metal cone/v dop. I could see the pyramid impression being better for a trillion though. Is the wax just a better surface to glue to? Does the softness help?


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 Post subject: Re: ethiopian welo opal questions
PostPosted: Tue Jun 04, 2019 12:17 pm 
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rattlesnakeagate wrote:
In the second technique, what is the advantage of having the wax impression if it does not closely form fit the stone? It would seem like the contact would be nearly the same with just a bare metal cone/v dop.
Good question. Any contact with the wax is less likely to damage the pavilion facets of a soft stone, and you could remove the stone by heating the dop gently to soften the wax, then put the stone in a small container with acetone to remove the residue more rapidly because of the greater exposed surface. But I usually just put the whole dop in the acetone jar and let it work over night.


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