The depth and table size of a diamond can have a big impact on its appearance and light performance.
In this write up, you are going to find out how these 2 factors affect the diamond’s overall cut quality. I will also reveal the recommended table and depth proportions to look out for if you want to buy a diamond with better brilliance and sparkle.
Let’s dive in…
This is the list of topics we will be covering here:
Where to find the depth percentage values in the certificate.
The depth of a diamond is its height (in millimeters) measured from the culet to the table.
In a grading report, there are normally two measurements of depth – the first is the actual depth measurement in millimeters (shown under ‘measurements’ at the top of a grading report), and the second is the depth percentage (see image above), which shows how deep the diamond is in relation to its width.
The craft of polishing a diamond is both an art and science. When light rays enter a diamond, the depth of a diamond affects how the light rays will travel and be reflected within it.
To create optimal light return and sparkle, the ideal depth percentage of a diamond would depend on its shape and may vary based on the intricate relationship with other facets (more details about this later).
Even though the depth percentage of a diamond doesn’t tell the entire story about its appearance, it can be used as a telltale sign for brilliance and value (stones that are cut too deeply are usually cut to retain weight from the rough).
The pavilion facets, in particular, should be cut to correct proportions so that light rays can bounce around within the diamond and be reflected out at the proper angle to the observer’s eye.
Dark looking nailheads and unsightly fish-eye effects are undesired consequences of bad depth proportions. Below are 2 such examples where things get really wonky when diamond depth is too deep or too shallow.
Total depth percentages of 56.6% (left) and 65.9 (right) are recipes for disastrous looks.
As I mentioned earlier, the ideal depth percentage varies with the shape of the diamond. A depth percentage that may be too deep for one shape might be essential for another due to the intrinsic behavior of the facet structure.
For instance, a princess cut with a 74 or 76 percent depth would still be considered acceptable and can yield an attractive diamond. On the other hand, a depth of 65 percent for a round diamond would be excessive and be detrimental to its beauty.
Where can you find the table size percentage? (FYI, this diamond has a 54% table).
The table refers to the flat facet of the diamond which can be seen when the stone is face up. It also happens to be the largest facet on a diamond and plays a vital role in the brilliance of the stone.
In a grading report, table percentage is calculated based on the size of the table divided by the average girdle diameter of the diamond. So, a 60 percent table means that the table is 60 percent as wide as the diamond’s outline.
If a diamond is round cut, gemologists can compute this value by dividing the table diameter, measured in millimeters by the average girdle diameter. For a consumer, this can easily be calculated based on the average physical measurements found in a grading report’s top left-hand side.
For fancy shaped diamonds, table percentage is computed by dividing the table width (measured at the widest part of the facet) by the width of the widest part of the stone measured in millimeters.
The main purpose of the table facet is to refract light rays entering the diamond and to redirect reflected light rays from the pavilion facets back into the observer’s eye.
It is widely misconceived that a larger table percentage would make a round diamond more brilliant than one with a smaller table. This is not true because there are other factors that contribute to the overall brilliance and fire of a diamond.
In short, a bigger table doesn’t mean better looks and vice versa. However, the size of the table can affect the fire dispersion properties of a diamond. Why?
To answer that question, you need to understand that fire is best observed at the bezel facets of a diamond. With a finite amount of space at the crown area, having a larger table would mean that bezel and upper girdle facets would now have less surface area and hence, dispersion decreases.
Vice versa, having a small table would allow girdle facets to disperse light more effectively while suffering from issues with brilliance. It is therefore important to strike a balance between light transmission through the table and color dispersion through the crown and upper girdle facets.
An insanely huge table of 81% will make the stone on the left devoid of dispersion properties.
Here’s a chart of recommended depth and table percentages that I personally use when shopping for high-performance diamonds. I’ve only listed the most popular shapes to keep things simple.
For round cut diamonds, I always look for a table between 54% to 57% and a depth between 61% and 62.5%. Besides table and depth proportions, I also follow a list of ideal proportions in crown and pavilion angles here.
Using the recommended table and depth percentages above, you can easily rule out diamonds that aren’t well cut. This will enable you to quickly narrow down your choices and help you to avoid low quality stones during your search.
If the shape you want to buy isn’t found above, use the navigation menu in the header and click on the respective link. This will bring you to the corresponding section with comprehensive information on the different diamond shapes.
Sleek pave engagement ring with super ideal cut diamond – WF
Combined, the depth and table percentages of a diamond play a major role in the stone’s beauty. It shows you how the stone has been cut in relation to its proportions and they are the first few values to help you instantly weed out diamonds with less ideal cuts.
While the variations in brilliance and sparkle may be apparent to the eye, the subtleties of proportioning may not be easy to discern. Bear in mind that the numbers and percentages are meant to be used as a guideline and a filtering tool.
Even if a diamond has values that lie within “ideal” ranges, you would still require additional performance data like videos and ASET imagery to determine its cut precision. For a step by step guide to selecting a diamond correctly, you should refer to this guide here.