Selecting a Diamond

When selecting a diamond for an engagement ring there are several criteria to consider.  These benchmarks are commonly refered to as the four C’s.  Below each are defined.  For more detailed information on each topic, click on the term.

Term Definition
Color The diamond’s color usually refers to the absence or presence of a yellow tint.  A color grade of “D” means that a diamond is colorless and a color grade of “Z” is the darkest yellow.  Diamond color progressively gets more yellow from D to Z.
Carat Weight A carat is not the physical dimensional size of the diamond but rather its weight, or more precisely its mass. 1 carat = 200 milligrams = 100 points
Cut The diamonds cut refers to the dimensions and proportions to which the diamond is cut.  Cut is critical in order to obtain maximum diamond brilliance.  Sometimes cut is often confused with or associated with style and shape.
Clarity The clarity of a diamond is the absence or presence of flaws, scratches, or mineral deposits inside the stone.  Click the clarity term to see the grading chart.


These criteria have been used for years to help customers understand the uniqueness of diamond and how that uniqueness equates to price.  Any jewelry retailer worth visiting will be able to relay details about a specific piece in their shop by using the terms listed above.

After you have determined the criteria of the diamond you want, be sure to look at the diamond’s certification to ensure those qualities.


A diamond’s cut refers to its dimensions or proportions.  Cut also carries with it the idea of shape and style.  Some will argue that a diamond’s shape and cut are two different things, and they would be right, but for a time now some dealers have started to use one word to mean the other and vice versa.  So, this section will help you to recognize the different types of diamond shapes and cuts as well as how to tell if the cut is a good cut.

A diamond can be cut into many different styles and shapes such as Round, Pear, Radiant, Heart, Oval, Princess, and Marquise.  Some of these shapes and styles are self-explanatory as to their general appearance.  One of the most common diamonds for engagement rings would be the round diamond.

The dimensions to which the diamond is cut have a large impact on the diamond’s appearance and price.  The stone should be cut in such a way as to reflect as much light as possible back out of the top of the diamond.  If the pavilion, the bottom half of the diamond, is too shallow, the light may pass through the stone.  If there is too much depth, the light may exit out the side.  The first picture below illustrates an ideal cut, while the other two show poor cuts.

Before the dimensions for each type of diamond are give, several terms must be defined first.  Below is a figure that shows several critical parts and measurements of a diamond.  Depth and diameter are measurements and the rest are different parts of the diamond.

The most important formula used to maximize a diamond’s brilliance is the formula for depth percentage.  Other noteworthy metrics are table percentage and length/width ratio.


Few, if any, round diamonds are perfectly symmetrical.  The length/width ratio is determined by taking different diameter measurements on the diamond.  A perfect round diamond would have a 1:1 (1 to 1) ratio.  Other shapes will have other varying optimal ratios.  When looking for a diamond, its table and depth percentage will be found on its informational certificate.  Also on the certificate will be the diamond’s measurements.

        Example:  4.94-5.00 x 3.04

The first number is the smallest diameter measurement. The second number is the largest diameter.  The last number is the diamond’s depth.

Below is a table that gives values for a round diamond’s cuts.

  Ideal Excellent Very Good Good
Depth % 59% – 62.7% 58% – 63% 57% – 64.5% 56% – 65%
Table % 53% – 57% 53%-60% 53% – 62% 52.5%-66%


Other optimal shape specifications seem to be a bit inconsistent between sources.  Just remember, with any diamond you want the light to reflect back up at you in full brilliance.  You do not want to be stuck with a diamond that you can see through or a diamond that is dull and lifeless.

Finally, there is a couple of parts on the diamond yet to be mentioned: the girdle and the culet.  It is best to have a thin diamond girdle and a small to nonexistent culet.  The easiest way to determine these characteristics on a diamond is again by looking at its certification.


A diamond’s color usually refers to how clear or yellow the stone is.  Diamonds come in a variety of colors such as black, brown, green, or pink. These stones are known as “fancy diamonds,” but most people are looking for a stone that is completely colorless when it comes to an engagement ring.

Color Grading

Diamond color is usually graded on a GIA scale ranging from D, colorless, to Z, strong yellow.  Diamonds graded in the D, E, or F range are usually very hard to tell apart to the human eye.  Sometimes the AGS scale is used.  In this case 0 is colorless and 10 is yellow.

To really see the difference in diamond color, it is highly recommended that you visit a local jeweler to see first hand the color difference. Be sure to select several diamonds of similar size, and compare their colors over a black or white cloth.


The price of the diamond will be affected by how clear the stone is.  The more clear the diamond, the more money you will pay.  However, this does not hold true for a diamond that is very yellow.  These are in the category of “fancy diamond” and can be very marketable and expensive.  Some people actually prefer a slight yellow tint in the diamond.  For these people, great deals await.


There is one other color characteristic known as fluorescence.  This characteristic has been described as a blue tint in the diamond and that the tint can be seen under a UV light.  Diamonds with a strong fluorescence are usually cheaper because it can cause some colorless stones to look cloudy.  Some fluorescence can be helpful though.  If a diamond is graded in the range G-I, a little fluorescence will actually cancel out some of the yellow color and because the diamond has a grading that indicates it is not colorless, the customer can end up with a much better price.


Clarity refers to a diamond’s absence of flaws such as fractures, cracks, mineral deposits, or scratches.  Such flaws are often referred to as inclusions.  For convenience, the amount of flaw in a diamond has been somewhat standardized by the Gemological Institute of America (GIA) and the American Gem Society (AGS).  Each has its own system which is shown below in the table.  On a diamond’s certificate it will usually have one of the grades below as a clarity grade.

Gemological Institute of America American Gem Society Explanation
FL (flawless) 0 No internal or external inclusions can be seen with a 10x microscope to a trained professional.
IF 1 Internally Flawless.  No internal inclusions, however there are some minor irregularities on the surface that can sometimes be removed with a polish.
VVS1 Very Very Slightly Included 1.  One tiny inclusion present under a 10x microscope.
VVS2 2 Very Very Slightly Included 2.  Two or three tiny inclusions visible under a 10x microscope.
VS1 3 Very Slightly Included 1.  Very Small inclusions visible with a 10x microscope.
VS2 4 Very Slightly Included 2.  Very Small internal flaws.
SI1 5 Slightly Included 1.  Small inclusions visible with a 10x microscope.
SI2 6 Slightly Included 2.  Small inclusions easily visible with a 10x microscope but not quite yet visible to the naked eye.
I1 7-8 Imperfect 1.  Inclusions easily seen under a 10x microscope and barely visible to the naked eye.
I2 9 Imperfect 2.  Many inclusions easily visible to the naked eye.
I3 10 Imperfect 3.  Many large inclusions very easily visible with the naked eye.


I highly recommend going to a local dealer and seeing these different grades for yourself.  Take time to look through the microscope at several diamonds.  This will help you if you decide to go with a dealer who does not use one of the appraisal systems above.

NOTE:  The 10x microscope that most dealers have is known as a loupe.


Certification is not one of the C’s in the traditional 4 C’s, but it should be.  Many dealers, whether in an actual store or an online dealer, carry diamonds that are certified by one of two authorities.  These certifying authorities are the Gemological Institute of America, the GIA, or the American Gem Society, the AGS.  With each diamond that passes through these organizations is a lab report that tells you everything about the stone.  Most dealers will graciously let you see the report and most all online dealers will post the report.  Below is an example GIA report.

As you can see, many of the metrics discussed in the 4 C’s appear above in the certificate.  In addition to the 4 C’s are scales and charts for reference to help decipher anything that is unclear. To help ensure authenticity, GIA laser inscribes their diamonds on the girdle with a number found on the certificate.  One can actually see the number on the diamond with a microscope.

I highly recommend getting a diamond that has a certification from a nationally known certification authority. Some dealers use their own system, that may be partial or biased, to certify diamonds .  Also there are many criminals who would gladly sell you a fake diamond for full diamond cost.

Look for the GIA, AGS, or other nationally known trademarks and you will always know exactly what you are getting.

I put an invaluable trust in these documents as I bought my own wife’s wedding ring from Bluenile by looking at a certificate much like the one shown above.  I was able to get a beautiful stone without even seeing it first.  Upon arrival the stone looked perfect and I had the certificate that could be used for independent verification if I was not satisfied.  In addition, this certificate can be used for insurance purposes if ever such a problem arose.