A diamond's culet is a pointed portion that serves as the tip or a very small flat area that connects all of the pavilion's facets. It is cut parallel to the table when viewed from the side.
Why is a Diamond Culet Important?
When a diamond is cut, the area at the bottom where all of the pavilion facets come together forms a very sharp tip, increasing the likelihood of chipping or other damage. The pointed portion will not sustain any impact, even if the stone is harder than other materials.
Compared to other gemstones, a diamond's culet serves a deeper function in addition to safeguarding the tip. Diamonds are susceptible to a phenomenon called “cleavage”. In the crystal of a diamond, ions and atoms create weak cleavage planes. It is parallel to the octahedral facets that, in the event of a hit to the tip, have the potential to break the entire pavilion.
Although culets has significant contribution in protecting the diamond from damage, the performance of the diamond is impacted by large sizes, which in some occasions, can be visible to the naked eye from the table. When a diamond has a larger-sized extra facet at the bottom, light can escape when it enters from the table, resulting in a poor light return that reduces brilliance.
How is Culet Graded?
The culet is regarded by GIA as a crucial element that can influence how the diamond appears face up when seen from the table. Therefore, to evaluate how the culet impacts the diamond's overall appearance and performance, visual evaluations under 10 x magnification and computer modeling are used.
Culet is measured and calculated by percentage relative to the diameter of the diamond. The final assessment still depends on visual observation. The culet size is computed using the below formula:
Culet Size (%) = (culet size (mm) / average diamond diameter) x 100
The GIA's classification based on octagonal culet shape is shown below. For the None, Very Small, and Small sizes, visual evaluation is performed since, due to its almost insignificant size, it can be mistaken for subtleties like clarity.
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