The cut of a diamond refers to the angles and proportions of the diamond. As light enters a diamond, a well-cut stone will reflect the light from one facet to another and then disperse and reflect it through the top of the diamond. A diamond of good proportions will have more fire and brilliance. A diamond that is too shallow or too deep will loose light out of the bottom or sides of the stone reducing the brilliance.

The shape and the size of a diamond are easily seen while the differences in proportions may be more difficult to spot, even though it is the most important feature in determining the beauty of the diamond. Some of the elements in determining a diamond’s proportions are the table size, depth percentages, crown angles, girdle thickness, polish, and symmetry. Read below to learn more about some of these characteristics.

The table size is the size of the table relative to the diameter of the diamond. It is expressed as a percentage. To grade the table percentage of a round diamond, divide the longest table diameter by the average girdle diameter and multiply the result by 100.

To grade the table percentage of a fancy shape (anything other than a round), divide the width of the table by the width of the stone and multiply the result times a hundred.

Table diameters of fancy shapes are measured at the same point as their widths.

The total depth percentage is the depth from the table to the culet. It is expressed as a percentage relative to the girdle diameter. Depth percentage affects how the light will interact in the diamond, and thus impacts its brilliance. To calculate the depth percentage of a round brilliant diamond, divide the depth of the diameter by the average girdle diameter and multiply it by a 100. To figure the depth percentage of a fancy shape, divide the depth by the width, and then multiply by 100.

Brilliance in a diamond is also affected by the pavilion depth percentage, which is the distance from the girdle plane to the culet or point at the bottom of the diamond. It is expressed as a percentage of the girdle diameter. The depth can vary slightly because the table and crown size also affect the brilliance of the diamond. Round diamonds that have pavilion depths shallower than 38 percent often have a reflection of the girdle under the table that looks like a ring. This is known as a fisheye and often the stone will look dull or flat. Fisheyes may also be found deeper in the pavilion when the table percentage is larger than 67 percent. If the pavilion is deeper than 48 percent, the stone will appear dark in the center, which is known as nailheads.

Symmetry reefers to the cutter's skill in creating equality between corresponding parts of a stone, which is important in producing an equal display of fire, scintillation, and brilliance. There are no perfectly symmetrical diamonds but it is important that the diamond is round and the culet is in the center of the diamond. Other examples of symmetry variations include misaligned facets, off-center, table, wavy girdles, and table not parallel to girdle.

The culet of a stone is the facet at the bottom of a diamond. It is put there primarily for protection. A culet will look like a small white spot in the center of the table. If a diamond is cut without a culet it will come to a point at the bottom, however, it has little or no effect on the value of the stone.

For maximum scintillation, brilliance, and dispersion, good polish is essential. Polish of a diamond refers to how well the facets of the stone are polished during the cutting process.

The American Gemological Society is the world leading cut grader, and is the only laboratory which has created a scale for cut. The American Gem Society has produced the standard for cut, polish, and symmetry and is the only way to purchase a certified ideal cut diamond. Cut is very visible. A stone of ideal proportions will have the most fire, brilliance, and scintillation. AGS grades on a 0-10 scale 0 being ideal. A triple 000 diamond has ideal proportions, symmetry, and polish.

AGS Ideal Cut Ranges
Ideal Table 53-57%
Ideal Depth 58.5-62%
Ideal Pavilion Depth 42.2-43.8%
Ideal Crown 14.2-16.2%

Diamonds which fall outside these AGS ranges will still be beautiful. In fact, many people find that a 60% table, which is larger than AGS’s standard, is often very visually appealing. Many also find slight differences in percent ranges to be attractive. At Americus Diamond our sales professionals can show you cut differences and help you find your perfect diamond.