Here’s an overview of diamond pricing and diamond anatomy terms…
Diamond Pricing: Polish, Symmetry and Fluorescence
In general, the price of a diamond is determined by the Four C’s, however there are a few other factors that will also affect the diamond’s quality and its price. Three of these are a diamond’s Polish, Symmetry and Fluorescence.
This refers to the variations of the facets of the diamond. The facet surfaces can be misaligned relative to the girdle. The table or cutlet may be off-centered, or the table & girdle may not be parallel. Virtually any misalignment will affect the symmetry of the diamond
Symmetry is graded by the GIA as either poor, fair, good, very good or excellent. The more symmetrical a diamond is, the higher it is graded and the greater the price. Most quality diamonds fall in the range of Excellent or Very Good. The price differential between Excellent and Very Good is small, so select Excellent if possible.
After a diamond is cut it is polished and during this process, if it is poorly done, microscopic defects may occur. Polish refers to the appearance on the gem’s surface that is a result of this buffing. The polish affects the diamond’s brilliance and it is graded based on the appearance.
GIA rates it on a scale as: Excellent, Very Good, Good, Fair or Poor. Grades Good or better are not noticeable to the unaided eye. As with symmetry, most quality diamonds fall in the range of Excellent or Very Good, and the price differential between Excellent and Very Good is small, so select Excellent if possible.
When some diamonds come into contact with an ultra-violet light source for an extended period they produce an effect known as fluorescence. A diamond that has the effect will glow softly when it is held under an ultraviolet light.
The fluorescent effect is not dangerous to the wearer of the jewelry or the diamond itself. This is a unique naturally occurring lighting property that is exhibited in a number of minerals and gems.
Fluorescence is graded on the GIA scale from none to faint to medium to strong to very strong. Usually fluorescent is not noticeable under normal lighting conditions. As with symmetry and polish, the price differential between grades is small. Choosing a diamond with a rating from none to medium should be fine.
One exception, is the boutique jeweler Brian Gavin, who has a special line of “blue” diamonds, individually selected for fluorescence properties that accent the diamond instead of detracting from it. See the video and link below…
- Fluorescence, GIA (pdf)
Diamond Anatomy Terms
Below is some information about Diamond Anatomy Terms that you may find helpful in your diamond buying search:
The flat surface on the top of the diamond. It is the largest surface of a cut diamond.
The part that is just above the girdle. It consists of a large flat surface known as a table, and several flat surfaces below (facets).
These are the flat surfaces that form the outer part of the diamond. Each of the surfaces is angled, shaped and cut to produce a unique effect to the light entering the diamond. The facets reflect the inner crystalline structure of the diamond and give it a sparkly look. The surfaces can allow light to enter, be refracted and exit the diamond. They can also reflect light off the diamond.
The width of the diamond when measured through the widest point (girdle).
The outer part of the diamond with regards to the diameter. The girdle forms a band around the stone. This is the narrow rim that separates the pavilion from the crown.
The lower part of the diamond that is below the girdle.
The surface or tip of the gemstone. This is a tiny surface that is added at the bottom of the gemstone’s pavilion. The purpose of the culet is to protect the pavilion from being damaged or chipped.
When a diamond has been incorporated in jewelry, the culet protects the pavilion from wear or impacts. Most gemstones cut today either have very small culets or no culets at all.
The height of the diamond as measured from the top surface to the culet. The depth is measured in millimeters.
The total depth percentage is equal to the total depth divided by the average diameter and the result multiplied by 100.
These are the angles at which the gemstone’s bezel surfaces intersect the girdle plane. These gentle slopes on the side surfaces that surround the table are responsible for the fire, or dispersion, in gemstones. When white light enters the different angled surfaces, it is broken up into a number of hues that end up creating the spectacular hues inside the diamond.
The crown angle is measured as the value of all the angles added together, divided by 8 and the result recorded to the nearest 0.5 degrees.
This is the value of the total diameter of the top surface of the diamond (table). This value shows how the diameter of the table compares with the overall diameter of the gemstone. The value is measured as a percentage. For example, a gemstone that has a table percentage of 70 means that the top surface is 70 percent as wide as the overall diameter of the gemstone.
To determine the table percentage of a round gemstone, the diameter of the table is divided by the average girdle diameter. The diameter is measured in millimeters. If the diamond comes in a fancy shape, its table percentage is calculated by dividing the width of the surface at the widest part of the diamond by the width of the entire stone. These measurements are also in millimeters.