Hi all, I’d like some information on ‘double girdles’ in coloured stones. This was a term recently told to me when I observed what looked like a doublet in a sapphire (using a microscope I saw a very distinct line, on an angle, above the girdle in the crown with very distinct saturation differences on the two sides. Gem was mounted so no other tests performed). I was told that I was seeing a “double girdle” that’s “common” (her words) in coloured stones. I’d love to know more. Appreciated.
The person who used this term, which isn’t a technical gemology term AFAIK, should have explained him/herself. There are doublets, basically stones with a deeper color pavilion (or possibly crown) and a lighter crown. Usually only one piece of the gem is actually a natural precious stone. So you could have a stone that will test as sapphire on the table facet (natural sapphire crown), but which has a pavilion that is some other, cheaper stone…it could be a clear or lighter color sapphire or some other species. Any way you slice it, it’s deceptive and usually a swindle. -royjohn
In fact, a woman brought in to my boutique a pair of sapphires, bezel set, diamond halo studs which she bought from another jeweller. She wasn’t pleased with them, said the gems didn’t look like the pic of the loose gems she was sent; these looked much darker. I didn’t do full tests because they were set but I took a peek. With the diamond tester, some melee came up moissonite but I don’t fully trust the tester on the melee and told her so. But, I thought the centre gems looked off. Put them under the microscope and there was a definite colour saturation difference on a sharp line on an angle above the girdle that looked like a doublet (that doublet ‘cap’ in the crown look). She looked in the microscope and saw it too. I wouldn’t fully confirm because I couldn’t do further tests due to setting but it certainly was suspicious as a doublet.
She then told the original jeweller who subsequently called me and gave me an earful (as it were!), including that it was not a doublet, it had “a double girdle” and that I as a gemologist should know what that is in coloured stones. I did my GG and my FCGmA and I’m thinking I must have missed the chapter on “double girdles”. Thanks for the feedback!
Well, getting an “earful” from some unscrupulous dealer is a badge of honor in my book. If I’m remembering right, you could use an immersion fluid on the whole ring without harming it and you would see the separation even plainer that way. Just have to thoroughly rinse the piece afterwards. Don’t use bromoform or methylene iodide, as these can degrade the cement that holds the stone together. I’d use benzyl benzoate, which is common and non-toxic. -royjohn
Good suggestion! Love the sharing of info in this community. Thanks Royjohn.
While we are on the subject, is there anyone else with favourite doublet detection tricks they reply on??
Sounds like doublet for sure. Magnification is best way to tell especially with set stone that limits testing the pavilion to see if it has different RI than crown. But could be either synthetic pavilion or maybe less desirable color and have the natural for crown
Hi again, Pamela,
As Roland F points out, immersion won’t help that much if the RIs of both parts of a doublet are the same. But you saw the separation even without immersion. Immersion will be good to look for inclusions and to look for diffusion produced color that does not penetrate the whole stone, so it’s still useful. However, magnification is one of the cornerstones of gem ID. Separating synthetics from natural stones is primarily a matter of looking at characteristic inclusions. That’s why getting proficient with a 10X loupe and with using a stereo microscope with darkfield illumination (and other types of illumination) is so important. You could spend a good bit of time getting together a set of photomicrographs of, say, synthetic vs natural corundum. Those photos are out there on the internet, but you do have to look for them. Then you have to look for the synthetic and natural emerald photos…and so on. Thankfully there are not so many species which are valuable, but also have synthetic counterparts. Learning how to use magnification is a royal road to gem ID proficiency. -royjohn
Roland, that was Exactly the page I turned to in my lab manual as well!
Now, was I 100% sure? No, I wasn’t and told the client so. Again, it was bezel set with a halo around it and viewed while the client stood there. My final words was that it was suspicious. But that’s not really the story. The story was the original jeweller calling me up to give me heck and tell me the stone had a “double girdle”. That’s what I couldn’t get my head around. You ever hear of a “double girdle”. At some point she said it was “just above the culet”, which confused me even further.
Thanks Royjohn. Not ‘completely’ unfamiliar with 10x + m’scope having done both my GG and my FCGmA, although admittedly a tad rusty as my business focus is custom design (I started out in design at GIA). Yes, the images are helpful and I love the directory on the Inclusion Database on the Lotus website – the Hughes take exquisite images! Thanks so much for weighing in, most appreciated.
I just finished my GG at GIA less than a month ago. There is no such thing as a double girdle that would explain the color differences you described in a stone except that it is an assembled stone.
I don’t think anyone has mentioned looking for an inclusion to help determine assembled or not. If the inclusions stop at the girdle plane (or the cap) more evidence that it is assembled. If one inclusion stretches on below as well as above the girdle plane (or where you think the cap is), the stone can’t be assembled.
I’m going to agree that this sounds more like an assembled stone rather than a true double girdle.
A double girdle does exist and happens in a couple of different ways. The faceting process usually starts with the cutter grinding in one side (pavilion or crown) of the stone, and typically cutting in the girdle at the same time. Once transferred, the stone is then aligned in index, typically using the girdle as a reference. Some cutters will use a polishing lap to do this, and if the lap moves during the process it can polish in a slight line, creating an extra facet on the girdle. A cutter would refer to this as a double girdle. Since the girdle is not easy to see and doesn’t contribute much to the light property of the stone, production cutters will often leave it. Usually, this is only on one facet of the girdle.
There are two cases where there may be a double girdle all around the stone. The first is a re-polish or re-cut, where a new crown is polished into an old stone and the girdle may be used to align with the old pavilion. The slight alignment mismatch between the old cut and the new creates a distinct line on the girdle. In concept, you can polish the girdle out and get rid of it, but that would be at risk of the design and at the cost of stone weight. Recuts at a monetary weight size (say, .51ct) would do everything possible to avoid going to a next monetary size down (0.49ct) and if leaving a polishing line for the weight is needed, it’s done. Note that most recuts are more likely to lose 20% or more of the weight of the stone, so I would say that it’s not likely to be that close in the first place. The second is an intentional double girdle design, but those are pretty uncommon.
Thanks Peter, very interesting. So this term does in fact exist!
So, two things about the pair of sapphires I was looking at: one, not great quality and not so big (maybe 5 mm rounds) so would effort have been put into repolishing and thus the chance for the second girdle? And, secondly, wouldn’t any second girdle (intentional or unintentional) be parallel to the girdle? This very sharp distinction in saturation/look (no, not zoning) of the gem was at an angle starting at (or near, can’t recall) the girdle and going up towards the star/upper main (kite) facets on the other side. There wasn’t an ‘edge’ like a girdle would have, it was just a distinct angle, distinct gem differentiation.
And a third point perhaps, when the seller called me to sound off she described the second girdle “above the culet”. This may have been a ‘lost in translation’ moment (we started in French, switched to English) but when I said “above the culet?” (as I was further stumped at that point) she went off on a different tack so not sure if that’s really where she meant it was.
Your insight is appreciated!
In 42+ years in the gemstone trade, I have never heard the term Double Girdle before - not even in various countries where I have been purchasing gemstones/rough. Certainly sounds like a doublet, which is a well known term, including triplet, but have never heard of a Double Girdle and the term in itself is a paradox - " a statement or proposition that, despite sound (or apparently sound) reasoning from acceptable premises, leads to a conclusion that seems senseless or self-contradictory."
“double girdle” = Doublet. Point.
Not a gemologist, only 50+ years with gems in hand.
I would call the jeweler and say he doesn’t know a doublet. You can turn him in to better business bureau. He lied to sell the piece. Shame on him.
Much appreciated! I am pleased to hear I’m not as ill-informed as I was feeling when I was getting an earful from the other jeweller!
fdminasba, thank you. I did two certifications and the first thing I learned after graduating was how little I knew!. Your 50+ years are invaluable. Thanks for weighing in.
Yikes. I’m staying clear of her! I did call the client back to give her some of the feedback some of my suppliers and the participants here in the forum have given me but she has not responded. I think that’s the end of it for me.