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 Post subject: How to positively ID Black Diamonds
PostPosted: Tue Feb 28, 2006 9:25 pm 
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I seem to remember that diamond testers don't react accurately with black diamonds - I think it was due to the treatment/coloring agents? Does anyone have any experience with these?

I have some 6 mm round earrings in for appraisal that are so dark that practically no light passes through them, so I cannot use inclusions to ID them. SG is out because they are mounted. RI on both diamonds and hematite are OTL - so this doesn't help. The heft doesn't seem to be hematite. They test as moissanite on the thermal tester, which is a typical reaction for black diamonds.

Does anyone have a sure fire way to determine if a mounted black diamond is actually a diamond?


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PostPosted: Wed Mar 01, 2006 1:17 pm 
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Snizzy, there doesn't seem to be a lot of published report's on black diamond ID but I did find this link.

http://www.gaaj-zenhokyo.co.jp/research ... _11en.html

If you can use strong transmitted light through the stone it should appear to be very dark green or blue green as apposed to black.

I believe irradition is used to even out the color of the highly included natural black diamonds.

Maybe if you can manipulate the piece, you can close the iris diaphram down to a small opening and switch to brightfield on the microcope to see if there is transmitted light and inclusions.

Just a thought. I've never had a chance to examine any.


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PostPosted: Wed Mar 01, 2006 8:49 pm 
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Thanks for the link, JB. 8)

I was able to locate my old data from when I had this issue in the past, and black diamonds can contain trace elements of hematite and boron which can throw off the thermal conductivity tester to read "moissanite".

I haven't had time to look at the earrings that were brought in for appraisal yet, but my first impression was they were so dark and so shiny that they could easily pass for hematite or faceted onyx. I am hoping I can get some light transmitted through them. If not, I may ask the customer if I can have my goldsmith take one out of the setting and do a S.G. test on it.


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 Post subject:
PostPosted: Wed Mar 01, 2006 10:33 pm 
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Hey Sniz,

Since you probably can't do a chemical analysis on these stones and there are no black diamond experts jumping in here, let's approach this the old fashioned way.

Hematite, marcasite (a form of pyrite) and black onyx (dyed black chalcedony) would all be opaque gemstones, so you would not expect any light transmission through them which would narrow the possibilities if they do in fact transmit light.

I haven't had black diamonds to examine, so I don't know if they can be totally opaque. If they can be, would the luster be different than the metallic luster of hematite and marcasite? Diamonds are hard so would the polish be better on the diamond and the facet junctions sharper than softer stones like hematite, marcasite and black onyx?

I don't know all the answers for the black diamond separations but it seems as if some serious observation may eliminate some possibilities.
Keep us informed when you get a closer look at these. It was a good question we can learn from when presented with mounted black diamonds.


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 Post subject:
PostPosted: Thu Mar 02, 2006 1:10 pm 
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Black diamonds (actually a very dark green) can be irradiated aswell, so that is a nice call to make. InColor in Ohio does that all the time.

Prices of black diamonds are well below the prices of moisanite (in general), so I don't see why someone would produce black moisanite.
Sounds like the effort you put in is more valuable than the stone itself.

Ofcourse it's always a frustration if you can't make the correct call, so I would go with the option of having the stone removed, tested and replaced. At the customers cost ofcourse.

With set stones you have one hand tied behind your back.

Just state your observations with all its limitations and doubts in the report.


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 Post subject:
PostPosted: Thu Mar 02, 2006 1:39 pm 
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Well, I had to put forth some effort as my client wants an insurance replacement cost, as the earrings have great sentimental value to her and her house was recently broken into, so she wants her earrings insured.

When I am able to examine them on Monday, I will take an RI to rule out onyx, and then my only options are to try to get some transmitted light to show through them - ruling out hematite, or removing one stone for an S.G. reading.

There are conflicting views regarding black moissanite.

This link implies that black moissanite is indeed on the market:
http://diamonds.goldenmine.com/content/jew-bla-dia.asp

I have emailed some moissanite suppliers and have been told that black moissanite is not being created as it would not be cost effective at this point in time. The only link I could find regarding black moissanite being marketed is this one: http://www.geolite.com/moissanite.htm

Here is a link that may explain the metallic luster that I am seeing on these earrings, if they are indeed moissanite: http://www.mindat.org/min-2743.html

Do black diamonds also have a metallic luster due to treatments and/or possibly containing hematite and boron?


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 Post subject:
PostPosted: Thu Mar 02, 2006 3:45 pm 
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Here are a couple of URLs that might give more information if you don't already have them. Also, an email to Martin Haske might be helpful since he's obviously studied the issue.

http://journal.pricescope.com/Articles/ ... monds.aspx

http://www.gia.edu/gemsandgemology/1857 ... detail.cfm


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 Post subject:
PostPosted: Thu Mar 02, 2006 4:09 pm 
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Thanks for those links ROM. I didn't have the back issues of G&G so I couldn't get into the "meat" of the article.

One more article from Professional Jeweler that has a little information below. It appears as if some black diamonds are efficient enough at absorbing light that they can present a metallic luster. A tip at the bottom of the article suggests transmitting light through the girdle on some types of irradiated stones to see the darker body colors associated with certain types of treated black diamonds.

http://www.professionaljeweler.com/arch ... 01dn1.html

Quite an investigation we have going here. :shock:


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 Post subject:
PostPosted: Thu Mar 02, 2006 4:26 pm 
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I have the G & G article but no time to look it up at this moment. I'll do so ASAP and see if there might be other leads for you to follow.

ROM


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 Post subject:
PostPosted: Fri Mar 03, 2006 1:21 am 
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All,

The G&G article deals only with natural black diamonds from Siberia and involves very sophisticated testing methods. Skimming through it I didn't notice anything that turned a light bulb on over my head in regard to testing Snizzy's stones.

Have a magnetometer in your hall closet? You might test for magnetism as the Siberian stones exhibit that property. I seem to recall Hanneman has a little trick of floating synthetic diamonds (also magnetic sometimes) on a little 'raft' in water and using a strong magnet to test them. If the subject stone is naturally black and not irradiated the S.G. test might be affected by metallic inclusions of magnetite, hematite, etc. Perhaps that's the case with irradiated stones too.

Frankly, the notion of black diamonds leaves me utterly bored. Why bother? Diamonds are about brilliance and dispersion. If black faceted stones are wanted why not schorl tourmaline, black spinel, melanite garnet, black chalcedony (I have a 50-pound hunk of natural material that would cut a lot of little stones!) or black nephrite?

I know...never argue with a client.

ROM


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 Post subject:
PostPosted: Fri Mar 03, 2006 6:52 am 
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Rom,
Hey, good point. Once you irridiate a diamond black what it has left is surface luster and most blacks are quite grainy and don't even have that.

Brittish designer Steven Webster uses black sapphires set in white gold in some of his designs. I carry his work, quite effective. An updated marcasite look! Ironic since marcasite in sterling was originally a sort of low end diamond look alike look. He sometimes plates the piece with black rhodium which mimics (sort of) the look of old diamonds set in silver.

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 Post subject:
PostPosted: Fri Mar 03, 2006 10:38 am 
I would just do a simple scratch test with a corundum point on the girdle under high magnification of a microscope. Since you mentioned that it goes OTL, you are probably left with black CZ(which scratches like Haematite and other stuff),black mossanite and diamond, both which don't get scratch.

If it doesn't scratch, perhaps you can try doing the scratching with your sample mossanite reference stone or even carborundum grit. I didn't suggest scratching straight with moissanite because it may be tough to get your hands on them.

At least it narrows down your range of suspected stones. REMEMBER though, to ask for permission from your customer.

Other timeless ways would perhaps be in the way of checking for knife-edge facet junctions, and perfectly flat facet faces under reflected light etc etc.

Alternatively, you can take refractive index with a brewster angle refractometer.

I like black diamonds. They offer a refreshing metallic look that just stands out different.

There is however a sure fire way of telling whether the diamond is diamond :) Burn it with a jeweller's torch, and see how long the substance lasts. If it burns with a beautiful blue flame, you have a sure fire way of ID'ing them mounted or unmounted.


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 Post subject:
PostPosted: Fri Mar 03, 2006 11:46 am 
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Snizzy,

If you are able to take a ri reading, then probably also a brewster angle .. brewster angles are not affected by lustre and good polish.

The machine costs a few $, but it will give you a quick yes/no on the moissanite/diamond question.

When doing magnetic tests, you should also be weary of magnetic elements in certain alloys. (which I could remember which ones).


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 Post subject:
PostPosted: Fri Mar 03, 2006 1:24 pm 
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I believe that iron, cobalt, nickel and their alloys are basic magnetic elements. Also, that cobalt is now used on occasion as a platinum alloy.

Sniz, if worse comes to worse, you can send it to the Letterman show for a "Will It Float" segment. If it floats, at least you know it's not a diamond. :wink:


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 Post subject:
PostPosted: Sat Mar 04, 2006 7:35 pm 
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I love black diamonds, especially in those in-and-out hoops, where the front stones are white, and the inside back of the hoop's stones are black. I was surprised to hear black diamonds don't test out properly using the diamond testers, because I thought I'd tested mine, so I dragged out all my hoops and black studs and tested them on the Presidium DuoTester, and sure enough, they all tested perfectly. So Sniz, if you have access to a Presidium, maybe you can make a determination, or at least get an indication of what direction to look in. :)

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