Quick - when you hear the word “girdle” what image comes to mind? You would probably think of the cinched in waists of yesteryear, where the goal of undergarments was to compress the midsection and create an appealing hourglass shape on women, and to hide that extra pudge on the gentlemen.
In the anatomy of a well-cut round brilliant (or any faceted diamond, in fact) the diamond girdle is something like the belt of the stone. It is the edge that allows the stone to be most effectively set into jewelry, as well as preventing damage. It is that small area between the crown (the top) and the pavilion (the bottom), where you may find a serial number, GIA Certification number, or perhaps even the mark of the person who cut it.
One factor that is often overlooked by consumers when purchasing a diamond is the girdle. There are four main finishes you will see on diamond girdles: bruted, polished, faceted, and lasered.
GIA takes diamond girdle condition fairly seriously, as a poorly shaped girdle can significantly impact the overall appearance of an otherwise beautifully-cut stone. All of that is just Gemologist talk for “What condition is the girdle in, and does it detract from the beauty of a stone?”
Think of it this way: Imagine finding the most beautiful gown that has ever been sewn. The only problem with it is that you hate the belt. The belt is rough and so poorly sewn into the garment that it’s actually causing hideous teeny tears throughout the fabric, effectively ruining the lines of the dress.
That’s what it’s like to have a poorly-bruted diamond girdle. Microscopic fractures can occur in the stone, which may be visible face up, regardless of the stone’s overall clarity or quality.
Additionally, when we grade diamonds we must also determine the girdles thickness, for too thin a girdle can lead to damage when the stone is later set in jewelry. Any jeweler will tell you that even the most beautiful diamond in the world can chip or break, despite their status as the “world’s hardest gem.”
It would be like taking that same dress from before, and trying to cinch in the waist with a shoelace. It is neither functional nor flattering, and nothing we want from either our gowns or our diamonds.
A thick diamond girdle is put there to add extra weight, so that a 5.00 mm stone can weigh 1 carat, despite the fact that a well-cut, well-proportioned round brilliant should be somewhere around 6.5 mm at 1 carat; essentially making a heavy thing appear smaller.
I know what you’re thinking. Why would anyone want to make a diamond appear smaller? There are a number of reasons why a cutter might cut a stone with bad proportions, and it usually comes down to weight.
Gemstones are sold not by dimensions but by weight, and a one carat stone will get a better price even if it is poorly cut, than a .89 carat stone. So, when you’re searching for your dream diamond, in addition to cut, color and clarity, I urge you to have a look at the girdle.