What is a culet on a diamond, and is it good or bad?
In the 14th and 15 centuries, when the cutting and designing of diamonds and their facets was becoming more developed, the culet was discovered.
The culet is simply a facet at the bottom of the diamond. Sometimes the culet is polished as a flat facet, also known as the culet being left open, and at other times, fairly common today, is polishing the culet to a point, also known as closing the culet.
When the culet is left open, or polished to a flat facet, it can be a large culet or a small culet. That measurement is basically telling you how flat they polished the point – a large amount of surface area or maybe they left it fairly pointed with only a small amount of surface area.
The benefit of the culet is that it protects the bottom of the diamond from chipping over the years. The point of the diamond is prone to that. The detriment of the culet is that because it is a flat facet that is parallel to the Table you can see right through the diamond from the top through the culet, and that can be mistaken as an inclusion. The appearance will not be of a surface, a diamond look, but will be of whatever surface color is behind it – like looking through a window.
A large culet will allow one to see through the diamond even more, making the diamond look as if it has some discoloration or a large colored inclusion right down the center of the diamond.
The mitigating factor is that once the diamond is set almost nobody looks at the diamond from the angle at which this is a problem. People look at the diamond from the sides, from an angle at the top, but nobody inspects the diamond looking straight down and inspecting it so thoroughly. In addition, the diamond is going to be worn in a ring on the finger, meaning the culet will not be affecting the diamond in this way. The “problem” of the culet is really only an issue when the diamond is sitting in the drawer of a diamond retailer being inspected by diamond experts.
A Round Brilliant diamond will generally be listed as having 57 or 58 facets. The difference between the 57 and the 58 facets is the culet. When the culet is ignored, because there is no culet, i.e. it was polished to a point, the diamond is listed at 57 facets. When the culet is open, it is considered an additional facet and is then listed at 58 facets.
The most serious effect of the open culet, if it is a large culet, is when the diamond is a with a large culet. Because of the flat appearance of the diamond, the large culet has the most significant effect of any other shape of diamond.
The culet size is mentioned on the certificate of the diamond, if the diamond is certified, and it will range from no culet to various combinations of small to large (e.g. very small, medium, slightly large, etc.).
In my opinion, the culet is not really anything to be afraid of, and as long as it is proportional and symmetrical with the diamond it should not affect the diamond negatively in any way.
by Phil Golden