Gemologists usually consider the cut to be the most important of the 4 C’s although few customers can see it. Even for a trained eye it is difficult to sort a very good cut, compared to an excellent cut. Most diamonds from a reputable establishment have a good cut or better. As you will see below diamonds are graded from Poor to Ideal.

Ideal
The utmost cutting skill combined with the best in brilliance and fire. A perfect balance.

Excellent
The same as above for the untrained eye, yet slightly more flexible regarding percentages. Some gemologists prefer the appearance of this range to Ideal.

Very good
This range is balanced between precise proportions and price considerations. Viewed by many as the best overall value in beauty and price.

Good
A good value, there are no acute flaws in the cutting process.

Fair
When compared to any cut above, even an untrained eye will see the difference in the brilliance. But you can acquire a decent diamond at a fraction of the cost.

Poor
Not recommended, they are usually too deep or shallow which does not enable them to reflect the light back on top. The light will escape from either the sides or bottom. Avalon Diamonds & Jewelry and Titanium Era Inc, do not sell diamonds with a poor cut.

Well cut
The diamond is well proportioned, light is reflected from one facet to another and then dispersed through the top of the stone. The Well cut diamond will usually have a cut ranging from Ideal to Very Good.

Deep cut
If the cut of a diamond is too deep, some light will escapes through the opposite side of the pavilion.

Shallow cut
If the cut of a diamond is too shallow, light escapes through the pavilion before it can be reflected.

The cut, or proportion, of a diamond is measured in percentages relative to the diameter of its girdle. The girdle diameter of each diamond is always considered 100%. Example: The girdle of a diamond measures 10 millimeters (100%). The table measures 5.6 millimeters. The total depth measurement is 6.1 millimeters. The diamond would be described as having a table of 56% and a depth of 61%. The table and depth percentages are the key to determining the best proportions.

The ratio between the depth and the width of the diamond will determine how the light

will be reflected back to you. The most light it reflects the better the cut is rated.

According to Marcel Tolkowsky (Mathematician and gem enthusiast) who, in 1919 developed the round brilliant cut, the ideal dimensions are as follows:

Table percentage: 53%
Depth percentage: 59.3%
Pavilion angle: 40.75 degrees
Crown angle: 34.5 degrees
Pavilion depth: 43.1 %
Crown depth: 16.2 %

Unfortunately Tolkowsky’s measurements do not include the girdle. The girdle is what secures the stone in the setting, a sharp girdle is fragile and brittle. A very thin or larger girdle is necessary to set a stone in any ring or jewelry piece.

A diamond's ability to reflect light determines its display of fire and brilliance. Diamonds are usually cut with 58 facets, separate flat surfaces. These facets follow a mathematical formula and are placed at precise angles in relation to each other. This relationship is designed to maximize the amount of light reflected through the diamond and to increase its beauty.

In many cases the visual differences from one classification to the next are so small they may be indiscernible to the naked eye. Science has produced sophisticated machinery that can measure every aspect of a diamond’s proportions. It is this precision that allows such strict standards to be defined. These guidelines give you the ability to not only make a selection regarding cut but to understand the underlying science upon which it is based. In any case a brilliant and scintillating diamond is ultimately the goal.

The lowest score becomes the overall cut grade. In order to classify each diamond with an overall cut grade the lowest assigned grade for any individual characteristic is always used. For example: If the table percentage falls within Ideal yet the depth percentage is in the Very Good range, the diamond is classified as Very Good.

The proportions are not the same for every shape. Many of the diamond shapes require their own guidelines in order to achieve maximum beauty. Due to the mathematical differences inherent in different shapes, the table and depth guidelines are formulated to maximize fire and brilliance. Although the numbers may be different, the goal is the same: a magnificent display that highlights the individuality and character of each shape.

The girdle is the outer edge of a diamond.

When purchasing a diamond, select one with a girdle that is not Extremely Thin nor Extremely thick. It usually has a frosted appearance. Many diamonds are also finished with a fully polished or even a faceted girdle. This characteristic does not affect the value of a diamond and is often more a reflection of the diamond cutter's preference. The girdle is rated in terms of thickness. Girdle size is generally defined as Extremely Thin, Very Thin, Thin, Medium, Slightly Thick, Thick, Very Thick, or Extremely Thick. The girdle can also be described as a range of these terms such as Thin to Thick. Avoid either Extremes.

Culet
The culet is the bottom point of the diamond. In many cases this point actually has a very small facet. The culet is referred to in terms that relate to the presence or size of this facet. The culet is generally graded as None or Pointed, Very Small, Small, Medium, Slightly Large, Large, Very Large, and Extremely Large. Smaller is more desirable.

Polish
This characteristic refers to the finishing or final polishing of the facets, or flat surfaces. Contrary to common belief, diamonds are ground and polished, not chipped away, until they reach their final form. Each facet is carefully fashioned by the diamond cutter to shine and be free from polishing imperfections. The polish of a diamond is graded from Poor, Fair, Good, Very Good, to Excellent. When purchasing a diamond, select one with a polishing grade of Good or higher.

Symmetry
This characteristic refers to the alignment and positioning of the facets, or flat surfaces. Each facet should be carefully positioned by the diamond cutter in proper proportion and relationship to the other facets. The alignment of each facet should be sharp and precise; improperly joined facet junctions can make a diamond appear uneven. The symmetry of a diamond is graded from Poor, Fair, Good, Very Good, to Excellent. When purchasing a diamond, select one with a symmetry grade of Good or higher. For titanium tension settings select very good symmetry or better since the stone is more visible than in more traditional settings.