Summary
If you’re in the market for a diamond, you may have noticed the ratings for girdles on laboratory grading reports. What do they mean?

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.

Reading time: 6 min

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.

diamond girdles - facet diagram

The girdle wraps around the largest part of the diamond. Cropped from “Diamond facets,” svg image by Danuthaiduc. Licensed under CC By-SA 3.0.

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.

comparison - diamond girdles

The diamond on the left has a thin to medium girdle thickness, while the one on the right has a slightly thick girdle. If the carat weight and cutting angles are equal, the diamond on the right would have slightly smaller dimensions. Images © James Allen. Used with permission.

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.

yellow diamond - diamond girdles

This yellow diamond’s thick girdle and steep pavilion angles improve its color but impair its performance. © James Allen. Used with permission.

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.

girdle reflections - diamond girdles

Every True Hearts™ diamond in this screenshot shows girdle reflections. Arrows added for emphasis. © James Allen. Used with permission.

Although many people who see a girdle reflection for the first time understandably believe it’s a crack or feather inclusion, a girdle reflection isn’t a clarity imperfection.

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.

fish eye effect - diamond girdles

Some poorly cut diamonds, like this “Good” cut diamond, can show a “fish eye” effect. © James Allen. Used with permission.

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.

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