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 Post subject: Color change sapphire
PostPosted: Thu Dec 31, 2020 2:08 pm 
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Hi everyone,

I hope I have this in the right place, still getting to grips with the format.

A bit of context first: This brooch came from a local auction, as I'm very green to gemology I usually stick to more reputable sources, but I'm looking to increase my knowledge and make my own strides too and this piece stuck out. It was simply listed as 'Yellow metal brooch with purple stone' - about as vague as you can get and I bought it for less than the scrap gold price. The mount tests as 9 carat gold and the style of the piece could date it anywhere from 1880-1930 with 1900-1914 being the most likely given the style, pin etc. Of course this doesn't mean the stone is necessarily contemporary.

The stone is strongly purple in incandescent light and blue with steel/teal tones in fluorescent light and tests as corundum on a thermal meter, so it seems pretty likely it is a colour change sapphire. It's about 15 carats and of course it's most likely to be lab grown, but I'm having trouble seeing the tell-tale signs. I have a couple of other larger ruby and sapphires, and I can discern the curved striae in those with a 10x loupe. This stone seems cleaner although there do seem to be some small inclusions, but they are too small to resolve with my loupe, it is further complicated as the facets have fine polish lines on the surface and these also reflect through making observation difficult.

Finally the question - is there any other good way to determine that it is synthetic without a microscope (which I don't currently have)? I'd rather not send it to a lab to spend a lot of money confirming it's lab grown if possible. Leading to a secondary question if I'm out of options - are there any recommendations for labs in the UK that can test which don't charge half a months mortgage!

Quick (poor quality) phone snap to give you an idea what it looks like too:


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 Post subject: Re: Color change sapphire
PostPosted: Thu Dec 31, 2020 3:24 pm 
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That looks like a classic synthetic "alexandrite like" corundum. Don't waste your money sending it to a lab.


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 Post subject: Re: Color change sapphire
PostPosted: Thu Dec 31, 2020 3:41 pm 
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The size estimation you give can be a tell that it may likely be a synthetic. And my experienced guess would be the same as previously post stated.

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 Post subject: Re: Color change sapphire
PostPosted: Thu Dec 31, 2020 5:03 pm 
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Thanks both, and yes I agree - but I also was hoping to learn if there were any tests I could apply to confirm this without a microscope. :)


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 Post subject: Re: Color change sapphire
PostPosted: Thu Dec 31, 2020 6:14 pm 
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Just out of humor, marry a gemologist with a microscope. :lol:

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 Post subject: Re: Color change sapphire
PostPosted: Thu Dec 31, 2020 10:07 pm 
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Finding growth lines is more a function of lighting, and orientation rather than magnification.

You may be able to see some curved striae with a loupe, pinpoint light source in a low light room, and immersion cell. Polarized light sometimes helps too.

Growth lines are generally more difficult to find in less color saturated material.

I have not tried them, but maybe one of those small portable darkfield loupes will work as well.


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 Post subject: Re: Color change sapphire
PostPosted: Thu Dec 31, 2020 10:38 pm 
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glhays wrote:
Just out of humor, marry a gemologist with a microscope. :lol:


An afternoon coffee would work for me. Nothing too serious. 8)

Agreed. I also believe this to be a vanadium doped synthetic flame fusion sapphire

I used to have one of these years ago:
https://www.amazon.com/Professional-Han ... 316&sr=8-7

Works pretty well. Try to rig it up with some white tissue paper on the front of the light source. Diffused lighting makes it easier to see curved growth lines.


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 Post subject: Re: Color change sapphire
PostPosted: Fri Jan 01, 2021 6:48 am 
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glhays wrote:
Just out of humor, marry a gemologist with a microscope. :lol:


Haha, my wife says this is an unacceptable solution!

1bwana1 wrote:
Finding growth lines is more a function of lighting, and orientation rather than magnification.


Thank you, I have an old gooseneck engineering inspection lamp somewhere which has a near point source of light, I will investigate further with this and see if it helps. I don't have a polarised light source, although I do have an old laptop and I seem to recall the light from the screen may be polarised? Will check.

Barbra Voltaire, FGG wrote:
Agreed. I also believe this to be a vanadium doped synthetic flame fusion sapphire


Many thanks - I do see similar pieces labelled as synthetic Alexandrite, but that doesn't seem right to me as this is corundum and I thought synthetic Alexandrite should be Chrysoberyl? Pleased to see you call it Sapphire as that is what I thought would be more accurate. The colours of this item are also purple and steel blue, no sign of green either.

Barbra Voltaire, FGG wrote:
I used to have one of these years ago:


That's very helpful, thanks. That should be useful in the field too which is where I have to make the decision - in the UK if you buy at an auction you can't return an item.


Another quick question - is there a known start date for production of this type of synthetic sapphire? It would be helpful to know if the stone may be contemporary to the setting or if it must be a later replacement.


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 Post subject: Re: Color change sapphire
PostPosted: Fri Jan 01, 2021 9:55 am 
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As others have mentioned the main thing would be to try some different lighting and see if that might show the curved striations.

Otherwise if you have a spectroscope you might be able to see the Vanadium absorption line but most of the time it won't be there. If you can get a clean RI reading on the stone, which you might be able to based on the picture, usually synthetic stones have lower an RI of 1.76 - 1.77 instead of the natural corundum going between 1.76-1.78. Also you could try a testing the reaction under both UV lights. The synthetic colour change corundum stone I have goes a dull orange colour under Long Wave UV and an orangy-green in Short Wave UV.

None of those are really definitive tests but they could all be indicators. I agree with your and everyone's assessment though for that size being the biggest indicator though. If it was a natural stone it would be in the tens of thousands and maybe hitting hundreds of thousands of dollars depending on clarity. That wouldn't have gone through the auction at less than scrap value if that was the case.

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 Post subject: Re: Color change sapphire
PostPosted: Fri Jan 01, 2021 11:34 am 
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S. Rautiainen wrote:
As others have mentioned the main thing would be to try some different lighting and see if that might show the curved striations


Many thanks (at danger of cross posting as I have another reply waiting approval). I think I might have it now, 1bwana1's suggestion of a point light source seems to have done the trick. I will have another check later but I think I've managed to isolate the curved striae using the point light and my loupe, still tricky as the surface polish lines go rainbow coloured when lit like this, but I think I'm there, may try and take a macro photo too.

I did try long and shortwave UV, it seems pretty much inert to both. I don't have a refractometer or spectroscope yet (I will be asking for recommendations in the right forum area shortly though). Currently I have just been using tools I can use quickly at estate sales etc to pick out things that look like they are worth further study, ie reject glass and obvious fakes). I do plan to break from the safety in future though so will be looking to increase both skills and equipment.

I did expect it to be synthetic due to the size and clarity (and only being set in 9ct), but the auction it came from is real hicksville mom & pop outfit and I've already had 18ct gold and diamond rings from there sold in group lots as silver & glass and an antique 18 carat gold and carved coral ring (sold as gold tone & plastic costume) - so it's a great place to hunt!


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 Post subject: Re: Color change sapphire
PostPosted: Sun Jan 03, 2021 12:33 am 
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C Elwell wrote:
Another quick question - is there a known start date for production of this type of synthetic sapphire? It would be helpful to know if the stone may be contemporary to the setting or if it must be a later replacement.


This method of creating stones has been around since the late 1800s so it wouldn't help. I'm not sure how long this specific type of stone (colour change, flame fusion synthetic corundum - sapphire) has been around specifically but the first stone made using the flame fusion was the ruby so it's been around for a while I'm sure.

As for your other response, glad you were able to confirm. I forgot to mention that not only varying lighting but also sometimes using a diffusion plate / coloured lens might help provide enough interference to see the curved striations as well. You can use things as simple as a facial tissue for the diffusion and you can pick up coloured lenses from most camera stores still.

I agree that some of the auctions and garage sale type venues might be a good place to find some good deals. I know I've picked up some old coral, amber, jet and even a few old european cut diamonds in gold or silver pieces. Just know that those are pretty lucky finds in most cases so for you to be stumbling across a $50,000+ stone in any karat gold would be pretty unlikely.

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 Post subject: Re: Color change sapphire
PostPosted: Wed Jan 06, 2021 11:22 am 
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Thanks to everyone for the help and info, and I think it has got me to the point of solid conclusion. Just to wrap this up I got out my macro equipment and here are the results:

https://postimg.cc/gallery/p8krBQ8

The first image is in North natural light, you can see all the polishing lines which was making it difficult for me to see the curved striae inside the stone. The next two are from a point source tungsten light, you can see some aberrations where lines intersect but it didn't look overly conclusive to me. The final two pics are lit with a xenon maglite and clearly pick up the curved lines in some areas (one indicated for quick reference). So unless I have gone horribly wrong I think it is safe to say 100% chance flame fusion sapphire.

Thanks again everyone.


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 Post subject: Re: Color change sapphire
PostPosted: Wed Jan 06, 2021 9:02 pm 
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From those pictures I can see the curved striations pretty easily so I would definitely agree you have a flame fusion sythetic colour change corundum-sapphire.

Nice pictures. I can see the curved striations really easily on the 3rd picture (brooch 1356).

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 Post subject: Re: Color change sapphire
PostPosted: Wed Feb 03, 2021 4:02 am 
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I am failing to see the curved striations on those photos.
Anyone care point them out at me?

S. Rautiainen wrote:
From those pictures I can see the curved striations pretty easily so I would definitely agree you have a flame fusion sythetic colour change corundum-sapphire.

Nice pictures. I can see the curved striations really easily on the 3rd picture (brooch 1356).


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 Post subject: Re: Color change sapphire
PostPosted: Wed Feb 03, 2021 5:16 pm 
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TheL wrote:
I am failing to see the curved striations on those photos.
Anyone care point them out at me?

See my image number 4, I have drawn an arrow to the lines, the curved ones running from about 1 o'clock arcing down to about 7 o'clock. Most of the other lines are parallel polishing lines on the facet surfaces.


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