When you view a diamond from the top, the girdle is the part of the diamond that creates the outer-edge outline. The diamond girdle is graded by experts from ‘thin’ to ‘thick’. Learn more in our guide, and discover the ideal girdle type for your diamond.
What is the girdle of a diamond?
The girdle is located around the circumference of the diamond, and is the thin section that separates the crown at the top of the diamond, from the pavilion, where the diamond tapers to a point below. Diamond girdles vary in thickness, and are graded according to the optimal proportion of the girdle to the rest of the diamond. GIA diamonds feature a unique code on the diamond girdle to verify their authenticity, visible only under magnification.
Diamond girdle grading
Diamond girdles vary in thickness, and are graded accordingly. The perfect diamond girdle will be perfectly proportionate to the rest of the diamond. A diamond girdle is graded by a combination of finding the percentage relative the diameter of diamond, visually by professional graders.
Extremely Thin - This can cause diamond weakness, and makes the diamond vulnerable to chipping or breaking. Setting a diamond with an extremely thin girdle is challenging because of this. An extremely thin girdle will result in a Poor to Fair cut grade.
Very Thin & Thin - Although slightly closer to the optimal girdle thickness, a very thin girdle is not ideal and still leaves the diamond vulnerable to chipping or breaking. A diamond with a very thin or thin girdle will have a Fair to Good cut grade.
Slightly Thin - This is almost the ideal diamond girdle thickness, risk of chipping exists but is significantly reduced. The cut grade of a diamond with a slightly thin girdle will be Good or Very Good.
Medium - A medium diamond girdle grade represents the perfect girdle thickness. The girdle is robust enough to minimise the risk of chipping or breakage, but appears slight enough so as to not negatively affect the look of the diamond. A medium girdle can be set within a ring or piece of jewellery safely and with beautiful, well-proportioned aesthetics. An Excellent cut diamond will have a medium graded girdle.
Slightly Thick - The diamond girdle is just a little too thick to be considered perfect, but still boasts a very good appearance and is resistant to chipping or breaking. This will have a Good or Very Good cut grade.
Thick & Very Thick - The diamond girdle is thick, meaning it can negatively impact the look of the stone, and even be seen reflected when viewing the diamond from above. The girdle will carry unnecessary carat weight (that you won’t see when the diamond is set), and the cut will likely be too deep, resulting in a Fair to Good cut grade.
Extremely Thick - The girdle will be visibly reflected within the diamond when viewed from above, causing a ‘fisheye’ effect. This negatively impacts the diamond’s sparkle and appearance, and results in a Poor to Fair cut grade. The girdle will carry unnecessary carat weight that won’t be seen when the diamond is set
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The most ideal diamond girdle grade is Medium - but you shouldn’t worry about this too much. Our experts will take care of selecting diamonds with such optimal details before your consultation - it's what we do!
What’s the best diamond girdle grade to choose?
The most ideal diamond girdle grade is Medium, but you could also consider Slightly Thin and Slightly Thick. Thinner girdles can leave the diamond vulnerable to chipping or breaking, and can be particularly challenging for goldsmiths to set safely. Thicker girdles are sometimes reflected into the crown of the diamond and create a ‘fisheye’ effect, and also carry an unnecessarily heavier carat weight that won’t be enjoyed once the diamond is set, but may cost you.
How important is the diamond girdle?
Although the diamond girdle has an impact on how well the cut and symmetry of the stone is proportioned, it is not the most important factor to consider when purchasing a diamond - so don’t worry about getting too caught up in the details. Instead, focus on finding a Very Good or Excellent cut diamond - which will have a well-sized girdle anyway, between Slightly Thin and Slightly Thick.
What are the different girdle types?
Faceted - Brilliant cut diamonds feature a faceted girdle. This is cut and polished to encourage and maximise internal light reflection, enhancing the diamond’s sparkle.
Polished - A polished girdle is smoothed from its rough form, but not faceted. This style is typically found on step cut diamonds, and helps to encourage light play, to a lesser extent than faceted girdles.
Unpolished - an unpolished girdle is left in its rough state, without facets. This can inhibit light return, and is not the optimal choice. Very few diamonds found on the market today will have an unpolished girdle.
Why does a thick girdle create a fisheye diamond?
A diamond with a poor cut grade can sometimes result in the girdle reflecting through the top of the diamond. This severely impacts the look of the stone, and creates a notably unattractive characteristic. A diamond with a fisheye features a dark grey-black contrasting pattern in the central section of the diamond, caused by the reflection of a thick girdle when a diamond is cut too shallow. A diamond with overly large table facets will also worsen the fisheye effect. You can avoid a diamond with the fisheye effect by considering either Excellent or Very Good cut grades - a fisheye diamond will never qualify for such high cut grades.