How to Choose a Diamond

Diamonds are the most popular gem used in jewelry today. They have great brilliance, plus a delightful quality know as dispersion. That is the ability to take in white light and throw back flashes of color or “fire.”

Diamonds are graded into dozens of categories. While this is helpful to the professional, it can be confusing to the average consumer. It can especially troublesome 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 of the data thrown at them.

Blake Lively Ring
Ryan Reynolds gave Blake Lively a beautiful, light pink diamond ring.

To help you, this article is divided into two parts.  First, there is a description of how diamonds are graded and what matters the most in determining a grade. Once you understand that, I make recommendations on choosing a diamond.

Diamond Grading – What matters most?

Diamonds are graded on four qualities, commonly known as the 4 C’s.

  1. CUT: The most important.
  2. COLOR:  The second most important.
  3. CLARITY:  Third most important, provided it is “SI” (Slightly Included) or better.
  4. CARAT: The least important.


This one of the hardest properties to judge, but it is the most important.  Choosing a well cut diamond requires paying careful attention to a few key characteristics.

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. The angles at which a diamond is cut has a lot to do with how efficiently it reflects light, which then impacts how well the diamond sparkles. (Note: If you are unfamiliar with this terminology, see our article on “Gem Cutting Terms.“)

The ideal angle for diamond pavilion facets is 41 degrees. This is usually quite convenient based on the shape of a standard diamond crystal (octahedral). Unfortunately, not all mined diamonds are able to be cut in excellent proportions. The diamond cutter is often faced with having to compromise between maximum brilliance and maximum yield (weight retention – keeping the most carat weight). The economics are such that, if the cutter removes too much material from the original diamond crystal, there is no profit in it.

Hence, many diamonds get cut at less than ideal proportions.

Diamonds have a high refractive index, which gives them their great brilliance. A little cheating here or there is insignificant. However, if the cutter varies a little further from the ideal cut angles, then the brilliance of the diamond begins to suffer. If the cutter varies even more, you end up with a gem that just does no’t stand up to others in terms of brilliance or fire.

While GIA and other certifying bodies assign cut grades to round brilliant cut diamonds, there really are no grades on any certificate that evaluate cut effectively. Most jewelers are familiar with correct proportions and can judge it from the shape (in the jewelry trade, they call it the “make” of a diamond).  If a jeweler refers to a diamond as a “heavy make” then that means the stone was cut to retain weight at the expense of a good cut in order to maximize the price.  Likewise, if a jeweler calls a stone a “spready make,” then this means the stone appears to “face up” or look like it weighs more than it actually does.  A “spready make” can sometimes impact the cut as well.

The best test for most of us is to simply compare the gems side by side. If you have two diamonds of the same grade and one is significantly brighter than the other, then the cut is the difference.

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.

Marquise Cut Diamond
Marquise Cut Diamond

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 at which these facets are cut vary (slightly to greatly) from those that give the greatest brilliance. This is a simple fact: the more facets that are cut at the ideal angle, the greater the brilliance of the gem.

Single Cut Diamond
Single Cut Diamond

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.

Round Brilliant Cut Diamond
Round Brilliant Cut Diamond

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.

Another factor to consider is the shape of the gem. An ideal cut gem should be symmetrical, not lop-sided. This point should be obvious, but sometimes it is helpful to point it out. A poorly proportioned gem can be camouflaged in it’s setting and you might not notice it until after you have paid for it.  You should always examine a diamond loose, not in the setting.

Though hard, diamonds are also somewhat brittle. You can see our article on Hardness and Wearability to understand more about why. This is important when thinking about the cut of a diamond because the girdle of the gem is the widest part when viewed from the top and the thinnest when viewed from the side. If the girdle of the diamond is cut too thin, it can present a weak area that is just asking for trouble. These illustrations will give you an idea of what normal proportions are. Some girdles get cut to a knife edge level of thinness and this is definitely something to be avoided because it can cause the gem to fracture or break.


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. 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” or “white.”

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.

Canary Yellow Engagement Ring
A canary yellow diamond is a refreshing alternative to a traditional diamond stone.

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.

While this low tech approach is accurate, it is also expensive and time consuming. A compromise is often made on smaller gems by grading batches within a range, rather than coming up with a specific grade. You will usually find diamonds under a carat graded as GH, or IJ, meaning that they are in that range.

This information is meaningful and saves you quite a bit of money. It costs over $100 to accurately grade a diamond. If you have a large diamond where subtle differences in quality grades make a significant difference in price, then it is worthwhile. However, that isn’’t cost effective for the majority of gems.


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.

Diamond Inclusions
Diamond Inclusions

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.

Synthetic Diamond with Flaws
Synthetic diamond with flaws and inclusions.

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.

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.

Then there is P1 and P2. They are not usually considered gem grade because so little light will pass through them. However, since they have the magic name diamond, they do show up on the market regularly.

Beware of ads that promote a “1 carat diamond ring for a very low price.” 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 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.


For those readers in the market diamond, IGS suggests the purchase of diamonds that are in the white range of color, (G, H, I or J,) and those with clarity grades SI1 or SI2. Visually these are bright and lively and make wonderful diamond jewelry.

Going down in clarity grading can occasionally be worth your while too, depending on the individual diamond and setting. Sometimes the “eye visible” inclusion that got it that ranking is insignificant and the overall appearance is still delightful.

Going down further in quality is rarely worthwhile. A lot of jewelers make their living by supposedly underselling the competition, when in fact they are selling lower grade gems. Without seeing better quality diamonds to compare, the customer is often convinced they are getting a great deal, but are disappointed later when they can make the comparison.

Please consider this factor carefully! While choosing a diamond is a personal thing and not everyone will have the same opinion, most folks will get more enjoyment from a smaller, higher quality dazzler, than a larger but mediocre gem.

People who are serious about their diamonds and get to look at a lot of them get a kick out of finding those rare gems that are nearly colorless or nearly clean under magnification. These gems are much rarer and therefore demand a higher price. But that does not mean they are much prettier, nor does it mean that the ordinary consumer will get more enjoyment out of them.

If you were to set two well cut diamonds side by side, one graded D, VVSI1 and the other G, SI1, you wouldn’t see much, if any difference with the naked eye. You would have a strong emotional reaction when you heard the prices though!

The point is simple: these are the rarest quality gems and the difference is only apparent to the sophisticated diamond appraiser who inspects them carefully with magnification.

SI2 GIA Clarity Graded Diamond
SI2 GIA Clarity Graded Diamond
SI1 GIA Clarity Graded Diamond
SI1 GIA Clarity Graded Diamond

There is occasionally a difference between a diamond graded SI1 and SI2. (SI1 is defined as “small inclusions, somewhat easy to find.” SI2 is defined as “small inclusions easy to find.”) When I look at a gem graded SI1 I usually see something like the first illustration. One or two tiny dark spots that have no effect on the brilliance of the gem.

Those graded SI2 have either larger inclusions, inclusions placed near the center where they are more visible, or many more of them. Some gems graded SI2, like the first illustration, will have no significant difference in brilliance. In an extreme case, where there are many inclusions, (even though none are large enough to be seen without magnification,) they may make up 5% or more of the visible area. That means a 5% or more reduction in brilliance.

To summarize, it is usually best to go with quality rather than size. Also, keep in mind — a colored gemstone may be a VERY good alternative to a diamond because Diamonds are NOT as rare as you may think!