Novembr 16-18—COLUMBIA, SOUTH CAROLINA: Annual show; The Columbia, SC Gem and Mineral Society; Fri. 10-6, Sat. 10-6, Sun. 12-5
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 Post subject: Troublesome Topaz....
PostPosted: Mon Apr 21, 2014 9:29 pm 
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Good day friends and faceters! I have been cutting a few small. clear topaz pieces and am having trouble polishing them. I have been working them mainly with alum oxide, but have tried 50K diamond as well....just planes of pits is all I gits.......HELP!!!

ken


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 Post subject: Re: Troublesome Topaz....
PostPosted: Mon Apr 21, 2014 9:51 pm 
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Is this strongly directional or all around? I'm sorry if I'm stating the obvious, but generally the cleavage plane won't readily polish in topaz, so if it's not oriented right you tend to have problems (again, I know that's a well-known concern, just getting it out of the way).
Some blue topaz has been known to be troublesome at this stage (presumably from radiation damage) but that seems unlikely in a colorless stone, unless it was one that was irradiated and just didn't take. I suppose that they don't just throw those out, though I think that stones are usually lightly irradiated first to see if there's any bluing potential at all, so this degree of damage wouldn't make much sense.
When it comes down to it, though, the nice thing about colorless topaz is that, barring specific sentimental value, if it isn't behaving it's cheap and easy to just get new rough which will.
Most everyone here knows more than me, those are just the very basics.


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 Post subject: Re: Troublesome Topaz....
PostPosted: Mon Apr 21, 2014 10:24 pm 
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the finest grit and the lightest pressure and patience...with a slow speed and lots of sweeping the lap...beating your forehead on the wall helps sometimes too!!


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 Post subject: Re: Troublesome Topaz....
PostPosted: Tue Apr 22, 2014 4:05 am 
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stairman wrote:
...beating your forehead on the wall helps sometimes too!!

...and this is what I have been doing. As for Scarodactyl's questions, it is not directional, just consistently constant, and the original color was a light peachy tan...exposure to light of day has cleared the stones (don't know if they were irradiated, but at 50 cents / gram who asks).

ken


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 Post subject: Re: Troublesome Topaz....
PostPosted: Tue Apr 22, 2014 10:45 am 
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At that price, put them on the back burner for a while at least. Try a piece from a different source and see what happens if you are determined to polish Topaz.

I find clear Topaz easy to polish with either oxide or diamond, oxide does seem faster although I will resort to 50k diamond if anything unusual happens, both on Batt or type metal. What polishing lap are you using?

Regards,

Sean.


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 Post subject: Re: Troublesome Topaz....
PostPosted: Tue Apr 22, 2014 2:11 pm 
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Topaz is one of my favorite materials to cut, behind garnet. I can get a good polish on it most of the time with oxides or diamond.

I do sometimes see problems with heavily irradiated material doing as you describe. I suspect the radiation has probably damaged the crystal lattice. Those pieces I usually consign to the fish tank rather than deal with the frustration to try to get it polished and dop something different.

_________________
"Distracted by something shiny."

Wayne Wilson


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 Post subject: Re: Troublesome Topaz....
PostPosted: Tue Apr 22, 2014 3:45 pm 
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Were they, perchance, from Pakistan (Gilgit/Skardu)? Those are almost always irradiated from colorless to get a variable orangy-brown which fades pretty readily in sunlight. I don't think they tend to be really heavily irradiated but it's possible that these were and the evidence (deep brown-black color) had been partially faded away.
One thing you might try is heating them, maybe to around 400c or so (enough to remove color centers/crystal defects in some topaz). It's possible that that would remove the defects causing the bad behavior. Or, if it's internal stress, they might explode or fall apart with heat--I've had each one happen once with topaz upon heating. So be careful if you go that route.


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 Post subject: Re: Troublesome Topaz....
PostPosted: Tue Apr 22, 2014 11:30 pm 
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Scarodactyl wrote:
Were they, perchance, from Pakistan (Gilgit/Skardu)? Those are almost always irradiated from colorless to get a variable orangy-brown which fades pretty readily in sunlight. I don't think they tend to be really heavily irradiated but it's possible that these were and the evidence (deep brown-black color) had been partially faded away.
One thing you might try is heating them, maybe to around 400c or so (enough to remove color centers/crystal defects in some topaz). It's possible that that would remove the defects causing the bad behavior. Or, if it's internal stress, they might explode or fall apart with heat--I've had each one happen once with topaz upon heating. So be careful if you go that route.

Yup...Pakistan... I did heat a couple, they really cleared up nicely and also cut and polished without problem, guess I will put the rest in the kiln for a spell.

Thanks guys.

ken


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