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 Post subject: IIb or not IIb
PostPosted: Sat Mar 31, 2012 12:13 pm 
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Did an appraisal yesterday on a diamond bought out of the country and deemed moissanite by a competetor. It tested moissanite with their tester but was obviously a diamond to me. I assumed their tester was malfunctioning, but out of curosity tested it on mine also. It also tested moissanite which kind of caught me off guard at the moment. It was not gray or blue in color, but I surmise it must be type IIb and that the electrical conductivity fooled the tester.
Anyhow, it led me to two thoughts. The first being that this situation could lead to all sorts of legal problems for people using these testers who can't visually identify a diamond, and second, wouldn't this be a good way to check all those irradiated blue diamonds to make sure that you really didn't have ten matched natural blues in a channel set ring. I had a light blue come in once and I stacked watch batteries on a battery tester, put the diamond on top and touched it with the probe. The meter moved a bit so it was off to GIA. If all blue IIb test moissanite, wouldn't it be more of a reliable test?

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 Post subject: Re: IIb or not IIb
PostPosted: Sat Mar 31, 2012 3:32 pm 
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Natural and synthetic blue diamonds that are colored by boron conduct electricity, while irradiated blue diamonds do not.
Note that not all natural-color blue diamonds are colored by boron, and thus not all will conduct electricity.

thermal testers are not reliable test, although for blue diamonds there is SSEF Blue Diamond Testerâ„¢,
Click here if you are not seeing the pdf below

[pdfview]http://www.ssef.ch/fileadmin/Documents/PDF/Blue_Diamond_Tester.pdf[/pdfview]

i myself encountered a Type IIb diamond which customer claimed to moissanite by thermal tester, of course with my examination i knew it was diamond i did explain to my customer almost ~0.1% of diamonds in the world are type IIb and because they are semi conductive the thermal tester confuses them with moissanite, as a demonstration i did successfully Conductivity tests by simple equipments but it was dangerous because i used wires placed around diamond and high voltage alternating current showing currents in multimeter :D very dangerous dont attempt to do it

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 Post subject: Re: IIb or not IIb
PostPosted: Sun Apr 01, 2012 12:45 am 
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Pardon my bluntness, but if one can't instantly tell a diamond from synthetic moissanite on sight, I believe they should turn in their gemological credentials.

I one needs a confirmative test, learn the Hodgkinson Method or drop the stone in a glass of water on a white background and shine your penlight on it.


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 Post subject: Re: IIb or not IIb
PostPosted: Sun Apr 01, 2012 4:14 am 
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In some moissanite testers the electrical conductivity is used to detect moissanites, for example this one: https://www.shannonsminerals.com/shop/i ... 00284.html

The test is done in two steps - first thermal conductivity to detect all conventional simulants, and if the stone have high thermal conductivity you apply electrical conductivity to separate moissanite (conductor) from diamond (not conductor). In the users manual of this tester it is stated that diamond also can be conductive in the case of type IIb diamonds.

IMHO, the electrical conductivity to detect moissanites is not a good method. Type IIb diamonds are electrically conductive and, on the other hand, I've had some moissanite that were not conductors for some reasons.

Of course you can use electrical conductivity to detect irradiated blue diamonds (type I), but be careful with synthetic blue diamonds, they are type IIb.

Other type of moissanite testers that only use thermal conductivity to separate both diamond and moissanites (like this one: http://www.igem.com/presidium-multi-tes ... ester.html) are not 100% reliable too, especially for small mounted diamonds. You can have "moissanite" reading for diamonds in some cases.

Moissanite property that will never fail is its birefringence. Observed with a loupe through main facets of the crown and focusing on the culet, you will see double edges. It's very important the correct orientation of the stone for this observation, you won't see double refraction in face-up view because the cutters always place the optical axis of moissanite in perpendicular to the table. With some experience, you will see double edges even in 2 mm moissanites with 10x loupe, but much better with higher magnification under binocular loupe.

Birefringence observed in moissanite (2 mm diameter stone):
Image

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 Post subject: Re: IIb or not IIb
PostPosted: Sun Apr 01, 2012 12:41 pm 
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Bill Hanneman wrote:
Pardon my bluntness, but if one can't instantly tell a diamond from synthetic moissanite on sight, I believe they should turn in their gemological credentials.


I don't think many trained people have trouble separating them by sight, but the testers are a crutch for a lot of untrained people. And no, you will never get them to do the Hanneman method if you can't get them to use a microscope in the first place. That is what I was trying to point out. I think there is a really big risk for stores to use the testers only.
Also thought that it would make a nifty back-up ID for blue irradiated melee, since they would test diamond, but not moissanite as would a type IIb.
Sorry if I wasn't clearer.

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 Post subject: Re: IIb or not IIb
PostPosted: Mon May 21, 2012 7:05 pm 
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http://www.adamasgem.org/mouse.html

http://www.jckonline.com/1998/08/01/bui ... moiss-trap


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