Diamond Girdles: 11 Facts You Need to Know
Buying a diamond but unsure about the girdle? Learn everything you need to know about diamond girdles, including thickness ratings and girdle inscriptions.
5 Minute Read
In this article, you'll learn everything consumers need to know about diamond girdles, from what they are to why they matter when buying a diamond.
1. What is a Diamond Girdle?
When looking at a diamond from the top, the girdle is the part of the stone that creates the outline. From the side, the girdle separates the pavilion, or bottom, from the crown, the set of facets around the top.
Most importantly, since the girdle touches the setting, it may experience knocks. So, diamond girdles need to be durable.
2. Diamond Girdles Have Thickness Grades
In most cases, girdle thickness won't affect your diamond buying decision. Any grade from "Very Thin" to "Very Thick" can give you a beautiful, durable diamond. However, avoid any diamonds with "Extremely Thin" girdles and examine diamonds with "Extremely Thick" girdles very carefully.
3. "Extremely Thin" Girdles Can Chip
If the diamond girdle is "Extremely Thin," it may not be durable enough to withstand daily wear. Prongs that hold the diamond in place can put strain on a girdle that's too thin, causing feathers. Exposed thin girdles can also chip. Because you have other options, avoid any diamond with this girdle thickness grade.
4. "Extremely Thick" Girdles Can Cause Poor Light Return
On the other hand, an "Extremely Thick" girdle isn't always cause for concern. If you're looking at a diamond with great performance and an "Extremely Thick" girdle, it would still make a great diamond engagement ring.
However, "Extremely Thick" girdles can often cause poor performance in a diamond. Some girdles are so thick that they make the diamond too deep. As a result, light entering the diamond from the top doesn't reflect back to your eye but instead escapes through the girdle or pavilion. If the light doesn't come back to your eye, the diamond simply doesn't look as good.
5. Thick Girdles Also Hide Weight
Moreover, a thicker girdle hides weight. Instead of appearing an appropriate size for its carat weight, a diamond with a thicker girdle will appear smaller. For example, a 1.2-ct diamond could have the length and width of just a one-carat diamond when viewed from the top down, because an "Extremely Thick" girdle could hide the weight as depth. This means you're paying for extra weight that you can't appreciate, and the extra weight also probably makes the diamond perform poorly.
6. Ranges in Girdle Thickness are Common
In most cases, girdle thickness is given as a range. This doesn't indicate poor cut quality and shouldn't be cause for concern. For example, the diamond in this video from James Allen has a girdle range from "Thin" to "Slightly Thick" but still performs well.
However, girdles that include "Extremely Thin" or "Extremely Thick" ratings in their ranges may have durability and performance problems.
7. Thick Girdles in Fancy Colored Diamonds Can be a Bad Sign
The value of fancy colored diamonds comes primarily from their color. Since their color is assessed face-up, instead of face-down like white diamonds, colored diamonds often have thicker girdles.
Again, a well-cut diamond can still have a thick girdle, but "Extremely Thick" girdles are more common in yellow diamonds, since they can boost the diamond's price significantly. However, that doesn't make them a great purchase. Check out the video of this yellow diamond from James Allen.
At this weight, a cushion-cut diamond should measure about 5.83 mm in length and width, so this diamond is more than 0.5 mm too short in both directions. In other words, this diamond is hiding about 0.20 carats in its girdle and is too deep for good light return.
8. Diamond Girdles Can Have Different Finishes
Nowadays, most girdles are faceted and polished. That means, like the rest of the stone, the girdle consists of several flat facets.
However, this wasn't always the case. Older diamonds may be polished in a single facet around the edge of the stone. Some may have a bruted girdle with a frosted appearance.
9. Girdles Can Reflect in a Diamond
If you look at the side of your diamond and see a line across it, about ⅔ of the way down, don't panic. It's most likely a girdle reflection. Because of how light moves through a diamond, light that enters through the girdle will usually come out through the pavilion. This doesn't indicate poor cut quality. It's just a side effect of the diamond cut.
Bruted girdles and thicker girdles have more noticeable reflections, but this doesn't indicate poor cut quality.
10. The Fish Eye Effect is a Reflection of the Diamond Girdle
In a well-cut diamond with proper proportions, girdle reflections won't show at the top of the diamond. However, a diamond with a wider table or a shallower pavilion may show a "fish eye" effect, where the girdle reflection in the pavilion of the stone reflects back to you. This unattractive result can look like a large circular inclusion.
If you stick with well-cut diamonds, you won't have to worry about this effect.
11. Diamond Girdles Can be Inscribed
The diamond girdle serves another important purpose. Gem laboratories can inscribe the girdle with a report number, allowing you to connect a laboratory report to the physical object. Laser inscriptions can also tell you if the diamond is laboratory-made or has undergone treatment for clarity or color.
Examining Diamond Girdles Before You Buy
When you're buying a diamond, the most important thing is seeing it perform. So, if you're buying online, you'll want to choose a vendor with closeup videos. If you're happy with the performance, just make sure that the diamond girdle isn't "Extremely Thin." Remember, a diamond with sub-par performance isn't worth your money.
James Allen and Blue Nile provide magnified, 360° videos of their diamonds, letting you find the one with the best performance within your budget. That's why we recommend them for anyone looking to save on an engagement ring.
Still, if you're not confident about finding a great-looking diamond, or if you want something truly unique, create an engagement ring with CustomMade. Their experts will help you find a top-quality diamond and set it in a ring created just for you.
A geologist, environmental engineer and Caltech graduate, Addison’s interest in the mesmerizing and beautiful results of earth’s geological processes began in her elementary school’s environmental club. When she isn’t writing about gems and minerals, Addison spends winters studying ancient climates in Iceland and summers hiking the Colorado Rockies.
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