The 4 C's of Diamond Buying
One carat equals 200 milligrams or one fifth of a gram in weight
For diamonds under one carat, each carat is divided into 100 points - similar to pennies to a dollar. 3/4 ct. = 75 points, 1/2 ct. = 50 points, etc.
There are approximately 142 carats to an ounce and because large diamonds are more rare, they generally have a greater value per carat than smaller diamonds.
GIA Color Scale
The GIA Color Scale extends from D (colorless) to Z (light yellow or brown)
Diamonds come in every color of the spectrum, but the most popular gems are colorless. Truly colorless, pure white diamonds are extremely rare and therefore the most costly. Stones are graded according to color designations based on how far they deviate from the purest white. Colorless stones are graded D, E or F. All three grades are considered colorless, but with slightly decreasing transparency. Color grading continues down the alphabet, with each letter designating a slightly darker tint. The best way to see the true color of a diamond is by looking at it against a white surface. Although the great majority of diamonds come in shades of white, yellow and brown, the gems also come in a spectrum of majestic colors, form red and canary yellow to blue, green and purple. These colorful diamonds, known as fancies, are valued for their depth of color, just as white diamonds are valued for their lack of color.
GIA Cut Scale
Excellent - Very Good - Good - Fair - Poor
A polished diamond's beauty lies in its complex relationship with light. The magnificent display you see is made up of three attributes: Brightness is the combination of all white light reflecting from the surface and interior of a diamond. Fire describes the "flares" of color emitted from a diamond. Scintillation describes the pattern of light and dark areas and the sparkle you see when the diamond, the light or the observer moves.
A diamond's proportions affect its light performance, which in turn affects its beauty and overall appeal. Diamonds with fine proportions, symmetry, and polish optimize their interaction with light and have increased brightness, fire and scintillation.
GIA assesses these factors for standard round brilliant diamonds in the D-Z color range.
Cut is also used to describe the shape of a diamond. The most common cut, the round brilliant, has 58 facets, or small, flat, polished planes designed to yield the maximum amount of light to be reflected back to the viewer. In addition to the round brilliant, other popular cuts include the princess, cushion, marquise, oval, emerald, radiant, pear and heart shaped.
GIA Clarity Scale
The GIA Clarity Scale includes eleven clarity grades ranging from Flawless to I3
A diamond's clarity is affected by any external and internal characteristics created by nature when the diamond was formed or as a result of the cutting process. Characteristics such as internal spots or lines are called inclusions. Although these marks make each stone unique, the fewer and smaller the inclusions, the more valuable the stone. Clarity is graded on a scale ranging from Flawless (FI) to Imperfect (I) with only a tiny percentage of diamonds ever achieving a Flawless grading.