The Four C's
Over a century ago, the Gemological Institute of America (GIA) developed a grading system for diamonds that has become the standard for the industry. Currently, there are several organizations that use different grading systems, but we have found they all relate back to GIA' s original system. Because it is the most common, we will refer to GIA's system.
There are four essential aspects of a diamond that determines its beauty, quality, and value. They are known as "The Four C's". They are Color, Clarity, Carat and Cut.
"Color" for a diamond, refers to the diamond's body color (not the flashes of color that a properly cut diamond displays). The closer to "white" (i.e. clear or colorless), the better. Very few diamonds have absolutely no body color. Those that are, are graded as a "D" color on the GIA Scale ('A', 'B', nor 'C' are used in color grading). "D" is the best there is, although E and F grades are also considered extremely fine and are often also called "colorless".
The GIA color scale runs all the way down to Z, with increasing amounts of color associated with each letter. A 'Z' color grade isn't bad. By the time a diamond reaches this level of color saturation, it is considered a "colored" diamond.
As with many products of nature, very few diamonds are totally flawless. Nearly all diamonds contain imperfections (also referred to as "inclusions"), such as tiny black or white specks, minute cracks, grain lines, etc. The pattern and type of inclusions are unique and can be very interesting. The inclusion might be another small diamond, a garnet, a piece of iron or even a bit of olivine (peridot).
The type, shape, number, and size of inclusions in a diamond are unique to only that particular stone. Because of this, inclusions act as fingerprints and make it possible to identify one diamond from another.
A clarity grade is really an "imperfection grade", because the fewer and smaller the number of imperfections, the more fire and brilliance the diamond will have (all other things being equal). The top of the scale ("Flawless") is the rarest (and hence, the most valuable). If a diamond falls below the scale (lower than I3), it is not gem quality and it is used for industrial cutting tools. Most diamonds mined (over 85%) are used for industrial purposes. Only the best are cut and displayed in jewelry.
The easiest aspect of a diamond to understand is its carat weight. Note that it is a weight, not a size (some people get that mixed up). A carat (abbreviated "ct.") weighs one-fifth of a gram or 200 milligrams. The carat size is further broken down into "points". There are 100 "points" to a carat. So, a 53 point diamond is just over a one-half carat.
Naturally, carat weight affects the price. However, in a "nonlinear" way. For example, a one-carat diamond will cost more than two half carat stones combined. Larger diamonds are rarer and therefore command a higher price (a higher price per carat).
In the diamond trade, the cutting and proportioning of a diamond (referred to as "make") are of critical importance. Proper cutting and proportioning release the fire and brilliance hidden within the rough stone.
In an ideally cut diamond, ambient light enters their top (crown) of the diamond, it is reflected and refracted by the lower (pavilion) facets and the crystal structure, then leaves the diamond through the crown facets. This is why a diamond sparkles so much. If a diamond has not been cut to ideal angles, the light will not contact the facets at the correct angle and less light will be reflected back through the crown facets.
Natural crystals are rarely symmetrical. Diamond cutters will cut through rough crystal in such a way as to retain the greatest value. This means the proportions might be a bit 'off' ideal. The further off "ideal", the less beautiful and the less value the diamond will command.
"Cut" is the least understood aspect of a diamond, and most people are unaware that there can be significant differences in value between a well-cut and poorly cut diamond.
Many people are unaware that a number of techniques are used to improve the clarity of diamonds. This is done by removing or hiding imperfections. All other things being equal, a clarity-enhanced diamond is worth less than one that is naturally beautiful. There's nothing inherently wrong with a gem enhancement, as long as the dealer discloses the enhancements so you know what's been done to the stone, and you're not paying for one thing and receiving another.
Two common techniques are laser drilling and fracture filling.
Many diamonds come from the earth with tiny black specks inside them. When the black spot is easily visible, it becomes a candidate for drilling.
About 30 years ago, high powered laser beams were first used to "burn-out" these impurities. To reach the "inclusion", a laser drill is used to create a tiny hole reaching deep inside the diamond. The laser's heat will vaporize a black inclusion or turn it into a less noticeable white color.
Sometimes a chemical substance is used to fill small cracks in a diamond. The effect of this treatment can be dramatic, turning an "ugly" diamond into one that is remarkably brilliant.
Detecting Fracture Filling can be quite difficult. The "dispersion index" of filler material is different from a diamond. It's close, but different enough so that a jeweler can detect it's presence by rotating the diamond under a bright light. At certain angles, the filler will create a "flash effect".
Fracture filling is what we call "semi-permanent". It will remain in the diamond under normal wear, but the filling can be removed by placing it in an ultrasonic cleaner for extended periods of time. The filling can also be burned by a jeweler's torch. It is common (and safe) practice for jewelers to apply heat (with a torch) to jewelry while the diamonds are still in place. So, if you have a diamond that has been Fracture Filled, you must tell the jeweler about the filling, so he can protect the diamond from heat. If you forget to tell the jeweler (or didn't know about the filling) and the filling is damaged, the diamond can be removed from the setting and sent to one of the companies that provide this service to have the filling re-applied. This cost is usually just for the shipping, removal, and resetting of the diamond.