Carat
A diamond's weight is the simplest of its characteristics to measure and is used to calculate one aspect of a diamond's value. The word "carat" is derived from the "carob" bean, which was first used to determine a diamonds weight. One carat is a unit of measure; equal to a fifth of a gram (Note: One-fifth of a gram of gold is equal in weight to a one carat stone, a 5 carat diamond is equal to 1 gram.). Each carat is divided into 100 points. For example, think of a dollar, having 100 cents or parts, i.e. quarter carat (0.25ct.) has 25 points, a half a carat (0.50ct.) has 50 points and a 1.00 carat has 100 points.

A larger diamond is more valuable simply because it is found less frequently in nature than a smaller diamond. As it is more rare, the price per carat increases as the diamond gets larger, however, carat weight has no bearing on diamond color, clarity, or cut.

Color
The majority of diamonds appear white in color, however, there are subtle differences, which Color Grading is intended to define. The Gemological Institute of America (GIA) Grading Laboratories use a color scale that ranges from D, E, F "colorless" to Z "strong yellow". The "colorless" diamond is more valuable than a diamond with a "hint of color to faintly yellow", although the grades between colorless and the "near colorless" G, H, I, and J can really only be truly appreciated by making a side by side comparison between diamonds of near equal size and shape.

Diamonds of color grade K and lower have enough yellow color to be visually apparent, yet can still be considered a choice by some as their cost is much less than higher color grade stones.

It may be beneficial to think of the diamond color grades as you might think of the endless variety of shades within a specific color of paint. Imagine you're painting a room and you've settled upon the color beige. You quickly discover that beige is available in a variety of tints and hues. Individually, from one shade or tint to another, the color difference is barely perceptible. It is when only in comparing shades that are several colors apart that the differences become obvious. So it can be with diamond color.

Cut
The way a diamond is cut, it's shape, as well as symmetry, and proportions, has a direct influence on the brilliance of a diamond.

The precision of the cut dictates the amount of light that the diamond will refract and reflect. The more expertly it has been cut, the greater its brilliance will be. When a diamond is cut to Ideal proportions, light is internally reflected from one facet to another and then dispersed through the crown, or top/table of the diamond. If the cut is too deep, then some refracted light will escape through the opposite side of the pavilion, or bottom of the diamond. If the cut is too shallow, then some light will escape through the pavilion before it can be reflected. A well-cut diamond is comprised of facets with the correct angles perfectly placed to maximize the diamond's brilliance. It is the quality of the cut and final polish that reveals the beauty of a diamond.

Clarity
Clarity Grading is intended to describe, to what degree and under what conditions a diamond is free of naturally occurring inclusions or blemishes.

A diamond is carbon that crystallizes in the earth for millions of years. During the crystallization process a variety of inclusions in the crystalline structure may occur. These inclusions, described by terms such as: cloud, feather, dark inclusions, etc., are found in almost every diamond and are generally caused by conditions present when the diamond was formed, though blemishes may also occur during the polishing process. The grading for clarity measures how many or few of these flaws are found, and gives special consideration to where they are located in the diamond.

Since nature makes nothing absolutely pure or perfect, those diamonds with few inclusions are most rare and command a higher price. The industry wide scale ranges from the low end or imperfect I-3, to the best "gem quality", the internally flawless IF/FL.

Certification
A diamond certificate is a document from an independent testing laboratory. That provides all the specifics regarding the diamond: shape, measurements, carat weight, color, and imperfections or inclusions. It also includes certain characteristics of the diamond's cut and any other comments regarding the specific diamond. Of equal importance is a numerical ID that identifies your diamond as being connected with its certificate.

Reputable diamond certification laboratories include Gemological Institute of America (GIA), The European Gemological Laboratory (EGL), The American Gem Society (AGS), The International Gemological Institute (IGI), and Hoge Road voor Diamant or Diamond High Council (HRD). These grading laboratories all utilize the same methodology of diamond grading including evaluating a specific diamond's 4c's by three separate gemologist. The final grade is determined by a majority opinion as to cut, color, clarity and carat weight.

There are other laboratories that exist that offer diamond grading certificates. They vary in reputation and accuracy and you should be advised to evaluate their credentials before choosing to entrust your diamond with them.