Whether you are looking to purchase your first piece of diamond jewelry or you need a refresher on how diamond quality is assessed, it is important to consider the "four C's" of diamonds: carat, color, clarity, and cut.
The first “C” is the carat size, which is the weight or mass of the diamond and is measured in carats. What exactly is a carat? A carat is a measurement of weight (200 mg) where the unit of weight is based on the carob seed. Most carob seeds are supposed to be of a consistent size and weight. The United States (following the lead of many other countries) adopted the metric carat definition on July 1, 1913. The metric carat is now the world standard for diamond weight.
The next “C” is the cut grade. A diamond's shape is sometimes called the “cut”. The cut grade describes the precision with which the diamond has been cut. The symmetry, the proportions, the angles, and the overall quality of the execution is known by jewelers as “the make” of the diamond.
Terms like “ideal” are used to describe diamonds that have superior cuts. There are tools for a novice to use to help determine how good the cut of a diamond is. However, it can still be confusing for the everyday buyer to determine whether or not the diamond of their choice is "ideal". Fortunately, organizations like the Gemological Institute of America (G.I.A.) came along to set up standards for grading the cut of a diamond. The G.I.A. assigns a grade for cut on their grading reports.
Beauty, however, is in the eye of the beholder as many stones are not cut to these “ideal” proportions. Some can have more or less dispersion (the prismatic colors) and more or less brilliance (white light reflections), because this may appeal to some people. The “ideal” is supposed to provide a balance, so it is a safe bet for most diamond lovers.
Most diamonds have what are called "inclusions" or external features that affect what is called the “clarity” of the diamond (or gemstone). These are imperfections that can be seen with the aid of a microscope or a ten-power loupe, although some can be seen with the human eye. The G.I.A. has established what is considered by most to be the standard for diamond clarity grades (besides all other aspects of grading).
Below is the scale from the Gemological Institute of America:
The G.I.A. has also established a standard for the grading of diamond color. The scale begins at D color and goes to Z. D is colorless, and Z is light yellow in the "fancy" range. Diamonds that go outside of the range can also have contributing colors other than tones of yellow. Various depths of grey and brown are also possible. Diamonds can also be in shades of red, orange, pink, blue, green, purple, etc. Some established colors have descriptive names for them such as the term “canary” for a bright and intense yellow color, “champagne” for a brownish-gold color, and “cognac” for brown to deep brown colors.