Diamonds are our most popular gem. They have great brilliance, plus the delightful quality know as fire, or dispersion. (That is the ability to take in white light and throw back flashes of color.)
Diamonds are graded into dozens of categories. While this is helpful to the professional, it can be confusing to the average consumer. I especially feel for the young couple looking for their first diamond engagement set. They want to gather enough information to make an intelligent decision, but can be overwhelmed by all the data thrown at them.
To help you I have done two things. First, there is a description of how diamonds are graded. Once you understand that, I make recommendations on choosing a diamond. Please read on.
Diamonds are graded on four qualities, commonly known as the 4 C’s… COLOR CLARITY CUT CARAT
The closer a diamond is to being colorless, the greater it’s value. When the current grading system was introduced in the 1930’s, diamonds were commonly called grade A, B, or C. So the current system began color grading with the letter D, to avoid any confusion.
Colors D, E and F are the highest grades. They are described as "colorless".
Colors G, H, I and J come next. They are described as "near colorless".
The colors from K to Z are tinted, (usually yellow or yellowish brown.) Those that are just lightly tinted, K, L and M are often said to "set white". That means that they are so lightly tinted that they will appear white if set in yellow gold. You would however notice their color if set in white gold or platinum.
As one gets further down the alphabet, the tinting gets stronger and the value lower. That is, until you get to the extreme. As the color becomes richer, you have a fancy colored diamond, rather than an off colored one. Then the value starts going up again.
Color grading is done by placing a diamond next to a set of previously graded gems. The color is compared to the graded gems to see which it comes closest to matching.
The clarity of a diamond is determined by the size and number of inclusions inside of it. An inclusion can be another mineral, a fracture or occasionally a void. Simply put, it is anything that will interfere with the free passage of light.
Just like with color, there are many clarity grades. They are judged by what an expert can see at 10 power magnification, under ideal conditions. The highest grade a diamond can get is Flawless. That means no inclusions can be seen at 10 power magnification. It does not mean inclusions can’t be found with higher magnification, nor should you assume it is the only grade with no inclusions visible to the naked eye.
Clarity grades use the letters V, S and I. They stand for Very, Small, and Inclusion. Progressing from Flawless, the grades are VVSI1, (Very, Very Small Inclusions One,) VVSI2, VSI1, VSI2, SI1 then SI2. These are the grades of diamonds that have no "eye visible" inclusions, those that can’t be seen with the naked eye. (Note, some SI2 stones will have small, eye visible inclusions.)
As we progress down the grading scale, there is I1 and I2. These have eye visible inclusions, but are still considered to be gem grade.
Beware of ads "1 carat diamond ring, $299". Just because something is a diamond, doesn’t mean it is a gem. In fact, the vast majority of diamonds mined are usually considered "industrial grade" and are used as abrasives. Many of these "industrial grade diamonds," those graded as P1 and P2, find their way into jewelry simply because they had the advertising appeal of being diamonds.
This one of the hardest properties to judge, plus there are a number of factors to consider. The first one has to do with the brilliance of the gem.
The pavilion facets of the gem are intended to act as mirrors, to reflect the light entering the stone, back towards the observer. However, the angle they are cut at has a lot to do with how efficiently they work.
The ideal angle for diamond pavilion facets is 41 degrees. This is usually quite convenient, based on the shape of a standard diamond crystal. Unfortunately, not all mined diamonds are in excellent proportions.
Diamonds have a high refractive index, which gives them their great brilliance. However, if the cutter varies a little further from the ideal the brilliance begins to suffer. Still more and you get a gem that just doesn’t stand up to others in terms of brilliance or fire.
Please understand that the above discussion assumes we are talking about round diamonds. Because of their symmetrical proportions, all the major facets can be cut at the same angle. The same does not hold true for other shapes.
Many people prefer a marquis shape. This is fine, but do not expect a marquis, or any other shape, to be as brilliant as a round. On a marquis it is necessary to cut a number of facets to accommodate the shape. The angles these facets get cut at vary, slightly to greatly, from those that give the greatest brilliance. This is a simple fact of physics: the more facets that are cut at the ideal angle, the greater the brilliance of the gem.
When looking for diamonds you may come across the terms, "Single Cut", "Old Mine Cut" or "European Cut". These are gems that only have eight facets running from the girdle down and eight up to the table. That makes a total of 17 facets. A standard round brilliant cut has 57 facets.
These "single cuts" are usually used on small accent stones, but occasionally you will find an older diamond of decent size with this cutting. Obviously, these gems won’t have the brilliance of a full cut diamond, therefore they aren’t worth as much.
This is by far the easiest of the factors to understand. Simply put, smaller diamonds are more common than large ones. Therefore smaller diamonds cost less per carat than large ones.
If you were to see a diamond broker’s price list, under each grade, the price per carat would go up with size. A grade of diamond that would cost $900 per carat in the ½ carat size might cost $1100 per carat at ¾ of a carat and $4000 in a full carat