Every diamond is unique. However, all diamonds share certain structural features one of which is the culet. Depending on its size, diamond culet can have a great impact on a stone’s appearance. Let’s see what this term mean and what you should know about it when buying diamonds.
What is a Diamond Culet?
The culet (pronounced ˈkyü-lət) is a tiny pointed area parallel to the table where facets of a diamond meet at the bottom of the pavilion. In simple words, the culet is the bottom tip or point of a diamond.
A diamond can either have a pointed culet which is usually described as “none” on grading reports or an additional rough or polished facet parallel to the diamond’s table.
The presence of a culet adds a facet to the diamond’s total number of facets. For example, a round brilliant cut diamond may have either 57 or 58 facets, meaning it has no culet in case of 57 facets and features a faceted culet in case of 58 facets.
In olden times large culets were a common feature of a diamond. For example, Old Mine and Old European cut diamonds always feature prominent culets. Today large culets are not desirable because culet provides an additional facet at the point of a diamond through which light can escape. This negatively affects a diamond’s fire, brilliance and scintillation and diminishes the stone’s beauty.
Diamond Culet Grades
The culet is described according to its size. The Gemological Institute of America (GIA) uses an 8-grade system to rate culets: None, Very Small, Small, Medium, Slightly Large, Large, Very Large, Extremely Large.
When a loose diamond is sent for certification, a gemologist will typically measure the culet size through a non-contact optical measuring device or a gemological microscope. The face-up view allows determining the culet’s size while the side view allows detecting its angle.
Culet Size % = Culet Size (mm) / Average Girdle Diameter x 100
The size of culets within the range of Small to Extremely Large can also be expressed as a percentage relative to the average diameter of the diamond, measuring from ≈ 1.5% to ≈ 15%.
Culet’s Effect on a Diamond
There is a debate going on among jewellers about whether a diamond should have a culet or not. There are arguments for and against it, that is why no uniform opinion exists.
First of all, let’s clarify that the main purpose of the culet is to prevent damage to the point and to protect the stone. Although diamond is the hardest known mineral (10 on the Mohs scale), the pointed end is at risk of cracking or breaking if accidentally hit.
The culet plays a significant role in a diamond’s light performance and appearance. Large culets are visible through the table as dark circles and allow light to escape through the bottom of a diamond. This negatively affects a stone’s sparkle and brilliance.
According to the modern cutting standards, the absence of a culet is more desirable. However, a pointed culet can easily be broken from high impact or when mounting the diamond into a setting. In fact, the culet is the most vulnerable part of a diamond, which is why it is necessary to secure the diamond in a protective setting to minimize the risk.
If you prefer to have a diamond with a faceted culet, it is better to go with Very Small or Small grades as these fall within the “Excellent” range. In case the culet is any larger, it will affect the stone appearance. This is especially true for bigger stones, large culets in them will look like a dark circle.