Diamond weight is measured in units called carats. A carat is divided into 100 parts.
Each part is called a point. A diamond that weighs one (1.00) carat also weighs 100 points.
Special diamond scales calibrated to a thousandth of a carat are generally used in the jewelry trade. Occasionally you may hear the term “four grainer” referring to a 1 carat stone. Each grain is equal to .25 ct or 25 points. If you think in terms of grams, 1 gram is equal to 5 carats. This metric equivalency provides a level of uniformity anywhere in the world.
Carat describes the actual weight of a stone—not the size.
Due to the limited supply of larger diamonds, the value of the stone rises proportionally as the weight of the stone increases. For example, four .25ct diamonds of the same quality will not equal the value of a single 1ct stone of identical quality.
The disparity becomes more noticeable as the size and quality of the diamond increases.
Bigger is not always better. A diamond’s ultimate value is based on a balance between the 4C’s: cut, clarity, color and carat weight. None of these factors is automatically more important than the others. All of them must be considered together to determine the true worth of a diamond.
The clarity of a diamond is the term used to describe the number and size of imperfections, inclusions or blemishes inside the stone. Inclusions occur within the stone, while blemishes are external in nature.
There are many grading scales used to describe clarity, however, that used by the GIA (Gemological Institute of America) is probably the most well known. The scale can be broken down as follows:
Grading is always performed with a 10 power loupe or microscope under proper lighting by a trained observer. Inclusions in stones graded I1, I2 and I3 can be seen by the unaided eye. In many cases the term “imperfect” will be substituted for “included” when describing VVS, VS and SI stones. Generally, diamonds in the I1-I3 ranged are referred to as imperfect 1, 2 or 3.
Unlike color that is often obvious to the eye, clarity grading is more subjective. A diamond may be graded from internally flawless to nearly the end of the GIA scale before an imperfection would be visible to the eye without magnification. Consequently, while clarity has a distinct effect on the value of a diamond, it often has a different impact on the beauty of the stone.
Color grading, using the GIA scale, ranges from D to Z, with D being colorless and Z being heavily (usually yellow) colored.
Colorless stones (designated D, E, and F) command the highest prices.
Diamond colors run somewhat in groups:
When grading diamonds, a non-reflective white background is used. Graders have to be careful about surrounding environment. Clothing color, lighting and color of the instruments used may affect the outcome.
Diamonds that naturally exhibit very intense pure colors, such
as blue, red, green and bright yellow are the rarest of all and as such command exceptional values.. These stones are not color graded with the scale above.
Color is one of the most noticeable characteristics of a diamond.
The setting of the diamond can affect the appearance of color. If the stone is colorless, a white gold or platinum setting will enhance the whiteness of the stone. But if the stone has a yellowish tint, a yellow gold setting may help mask the yellow tint, making the stone appear whiter.
Cut refers to the angles and proportions not diamond shape brilliance of a diamond depends on two key characteristics of its cut: symmetry and polish. Symmetry refers to the angles at which the “facets” (the stone’s smooth, angled surfaces) align. Polish refers to how smooth those surfaces actually are.
Diamonds are usually cut with 58 facets, or 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. When a diamond is cut to proper proportions, light is reflected from one facet to another and then dispersed through the top of the stone. The process of cutting also creates the diamond parts known as the crown, culet, table, girdle and pavilion.
Diameter: The width of the diamond as measured through the girdle.
Table: The largest facet of a gemstone.
Crown: The top portion of a diamond extending from the girdle to the table.
Girdle: The intersection of the crown and pavilion, which defines the perimeter of the diamond.
Pavilion: The bottom portion of a diamond, extending from the girdle to the culet.
Culet: The facet at the tip of a gemstone. The preferred culet is not visible with the unaided eye (graded “none” or “small”).
Depth: The height of a gemstone measured from the culet to the table.
The quality of the cut it’s what gives the stone its brilliant sparkle. When a diamond is well cut, light will enter the stone, bounce off the mirror-like facets and be reflected back through the top of the diamond, creating brilliance and fire. Brilliance is the return of light to the eye from inside the diamond (reflection of light). Fire refers to the prism effect, separating white light into a rainbow of colors (dispersion of light).
Ideal Cut Diamond – Nearly all light that enters the stone is reflected out of the top, designed to maximize brilliance.
Shallow Cut Diamond – Light will be lost out of the bottom or sides causing the diamond to lose its fire or brilliance.
Deep Cut Diamond – Light will travel out of the bottom or sides making the stone look dark and dull.