Diamond Buying Guide


Regarding diamonds, the terms shape and cut can be used interchangeably; however, when referring to the shape of a diamond one is describing the silhouette of the stone. There are 10 different shapes that are most common in today’s diamond market, and the shape of the diamond you choose depends entirely on preference. It is worth mentioning that the classic round brilliant is the most popular, with over half of stones being sold in that shape.


The round shape is the most popular choice because it shows more brilliance and fire than any other shape, when cut to Ideal Cut standards. A round shaped diamond will normally contain 58 facets and was the first of what is referred to as the “modern shapes”, first gaining popularity in the 1920’s.


The marquise shape, also called a football shape or the navette is a rare shape for an engagement ring. It’s long narrow shape was first commissioned by King Louis XV of France for his lover, Madame de Pompadour. A marquise shape contains 56 facets and has an elliptical shape, with the ends being pointed.


The symbol of love, a heart shaped diamond is particularly distinctive. The round pavilion allows the same type of brilliance of a round shape. When choosing a heart shape, it is important to pay attention to the length to width ratio; to little length and the heart will look squat, too much length and the heart will appear stretched and out of proportion.


The pear shape or teardrop has a rounded end on one side and a pointed end on the other. It’s relatively unique and can create a slimming effect on the finger, like the marquise shape. It has a distinctly feminine shape which can appear vintage in the right setting.


The emerald shape recalls Art Deco, with its rectangular shape, large table and pavilion. Because an emerald shape has fewer facets than any other shape the clarity of the diamond become paramount when making a choice.


The asscher is square in shape, and known for the distinct “X” visible in the table when viewed from above. It is like a princess shape, but has cropped corners. It is also like the emerald shape in that it is a “stepped” shape.


The cushion shaped diamond is a rounded square, popular since the 1830’s. The rounded corners give the diamond a romantic, vintage feel.


With the oval shape its wearer gets the slimming effect of the marquise along with the brilliance of the round cut. The oval was first introduced in the 1960’s, and is another shape in which the length to width ratio play an important role.


The radiant shape will give its wearer the grace of the emerald cut with the brilliance and fire of the round cut. The shape is rectangular and looks much like an emerald shape, but with much more facets accounting for its sparkle.


A square shape with pointed corners, it comes in second in demand to the round shape. Containing 76 facets, the princess shape allows for the brilliance of a round shape, but gives its owner a little something different.


The most important thing to consider when choosing carat weight is the person who will wear the stone; some prefer a large showy stone while others prefer something more delicate.

When purchasing a diamond one of the most important considerations is the weight of the stone. A carat, or a metric carat equals 200 milligrams (0.2 g), and can then be broken down into points as each carat is 100 points. Carat weight is used when measuring the weight of pearls and diamonds, and points can be used in the case of a diamond that is less than one full carat. In centuries past, carob seeds were used as a measuring tool for gemstones because it was incorrectly believed that there was little difference in their mass. In 1907 during the 4th General Conference on Weights and Measures the official metric carat weight was established, and quickly became the standard world-wide. It is important not to confuse the CARAT weight of a gemstone with the KARAT purity of gold; the two are not the same.

When the weight of a diamond increases so, obviously does the size of the stone. However, if you compare a one carat stone to a two-carat stone you will not see a stone twice the size; this is because a diamond is usually cut with a curve rather than linear fashion. It’s worth noting that when purchasing a diamond, certain carat weights are more popular than others (such as the 1.0 carat), and will be priced accordingly. Choosing a stone that is for example, .80 carat will give you a stone that is undistinguishable from its 1.0 carat counterpart, but at a much lower price. The term “total carat weight” is used to describe the weight of all the diamonds or gemstones present in any given jewelry setting. For example, if you purchase a pair of diamond studs the weight will be marked as Total Carat Weight or t.c.w.

When shopping for a diamond it is important to pay attention to the dimensions of the stone as well as the weight. The amount of surface area visible will make the diamond appear much larger; for example, a one carat diamond with the marquise shape will appear much larger in size than the same carat in the round shape. A one carat oval shape will yield approximately 10% more surface area than its round shaped counterpart. The cut of the stone can also play a large part; if the stone is cut very shallow it will appear larger than a stone with a deeper pavilion. The width of the girdle can also affect the size of the stone and its appearance. If you were to look at a princess or square shaped diamond in comparison to a round brilliant shape, the same carat size will look smaller (and is approximately 10% smaller) in the princess shape than the round brilliant. This is due to the mathematical calculations which must occur for the cut of the stone to be perfect. It’s the difference between the formula for the surface of a square, and the formula for the surface of a circle.


The word clarity itself means “the quality or state of being clear”, according to Merriam-Webster. When referring to diamonds, clarity relates to the existence, or lack of, inclusions and blemishes.

When a diamond is graded, clarity is one of the determinations. Finding a diamond which no inclusions or blemishes is extremely rare. Most inclusions or blemishes are not visible to the naked eye; when grading, a diamond master will use 10x magnification to aid in their discovery.

It’s important to note that the shape of a diamond plays an important role in its clarity; some shapes can mask imperfections due to their brilliance and number of facets such as the princess or the round brilliant. Others such as the emerald or the asscher will show these natural characteristics because of the size of the stones table.

The Diamond Clarity Chart

When the clarity of a diamond is graded a diamond master will use a set of master stones for comparison. The diamond grading scale is:

  • FL / IF – Flawless / Internally Flawless

  • WS1 / WS2 – Very Very Slightly Included

  • VS1 / VS2 – Very Slightly Included

  • SI1 / SI2 – Slightly Included

  • I1 / I2 / I3 – Included

Those included in the SI1 through I3 categories will most likely have inclusion or blemishes which are visible to the naked eye.

When choosing a diamond, the most popular category is the VS1 or VS2. The diamonds which fall into these categories may have blemishes or inclusions, but they are not visible to the naked eye and cost far less than their flawless counterparts.

The Slightly Included category, SI1 or SI2, is the next most purchased category. If one were to inspect the diamond up close they may see the inclusions or blemishes, but how often does that happen? For every day wearing, diamonds with these inclusions are just fine and the price savings can be significant.

The larger a diamond is, the easier it will be to see inclusions or blemishes, particularly in stones with larger tables such as the Asscher or emerald shape. When purchasing diamonds at two carats or less, clarity becomes less of an issue.

When a stone is graded for clarity the following considerations are made:

Size – the size of the inclusions or blemishes

Position – where is the inclusion or blemish at in the stone? Is it near the table where it is most visible? Or somewhere less visible such as the crown facet area? This is important for the clarity grade.

Number – How many inclusions/blemishes are present?

Color – Inclusions or blemishes which contain color are going to be noticeable against the clear of the diamond.

Nature – What is it, a blemish or an inclusion? As we discussed earlier, one is one the inside (inclusion) and one on the outside (blemish). A diamond can contain one or a combination of both.


It may seem counterintuitive; after all diamonds are clear in color. However, finding a completely colorless diamond is a rare occurrence which accounts for their enormous price tag. A diamond will normally contain a hint of color and will be graded as such.

When grading the color of a diamond, the diamond industry uses an alphabetical scale which runs D – Z. You may be asking yourself what happened to A – C? During the early days of diamond grading several systems were developed using ranges such as I, II, III, and A, AA, AAA, etc. Because of this the diamond industry leaders decided to create a scale which was completely independent of the previous attempts.

The grading chart is described as follows:

Grades D through F denotes colorless or practically colorless, a grading which will cost approximately 25% to 45% more than their counterparts.

Grade D – Denotes a colorless diamond, which will command the highest prices.

Grade E – Will be slightly less expensive due to a slight amount of color, only visible at 10x magnification.

Grade F – The least expensive of the “premium” stones, the color can only be detected at 10x magnification.

Grades G through I are considered near colorless. You may be able to detect a slight color in the stone when it is viewed from the side, but face up the color is undistinguishable. Diamonds in this color range are much more affordable than “colorless” diamonds.

Grade G – This grade is considered the best value in its color range. A G grade will be “nearly colorless”, and the color can only be seen when comparing to its colorless counterparts.

Grade H – This grade has slightly more color than the G grade, but again the color will only be noticeable when compared to colorless diamonds.

Grade I – The color may be slightly visible if the stone has not been set, but once surrounded by yellow or rose gold the color will be practically impossible to detect.

Grade J through L will show a stronger yellow or brown tint. Even through there is a slight tint of color, it is not usually noticeable in a yellow or rose gold setting. This is because of the warmth of the gold setting.

Grade J – These diamonds will contain tints of yellow or brown. This is once again a grade in which the color will be practically invisible once placed in a setting.

Grade K – Tinted more than the J grade, again with yellow or brown tints that become less noticeable when placed in a setting.

Grade L – Diamonds with a grade of L will show enough of a yellow or brown tint so as to be visible to the naked eye. It is not recommended to purchase this grade in the emerald or Asscher shape as the color will be quite visible.

Color differences in a diamond graded D through H are detectible by diamond masters using a two-step method. They will examine a diamond using 10x magnification, and they will also compare the diamond to their “master set” of diamonds to determine color. For the best value, diamonds with the grades G through I are the ones to consider for purchase.  


The shape of a diamond is often confused with the cut of a diamond however, they are different terms. Shape will describe exactly that, whether it’s an emerald shape, or a round shape. The cut of a diamond is one of the methods used to grade a stone, in terms of its sparkle. The “official” terms used to describe the sparkle of a diamond are Scintillation (light flashes), Fire (flashes of color), and Brightness (light reflecting from the Table).

The grading system for the cut of a diamond is as follows:

Excellent – This is the best cut diamond, which will show an even pattern of light and dark.

Very Good – Looking at a diamonds polish, scintillation and brightness, the proportions of a “very good” diamond will be slightly off, possibly causing darkness in the Pavilion.

Good – There are several factors which could cause a grade of “good” such as shallow Pavilion angles producing dark spots.

Fair – This diamond grade could be used when there is an irregular cut such as a shallow Crown or Pavilion which would cause darkness and a lack of contrast.

Poor – A grading of poor could be from several factors including a Girdle that is too large, a Table that is off centered, or a Pavilion which is too shallow. This stone will show little fire or brilliance.

Of the four C’s of diamond grading, the cut is the most important and the most technically difficult to determine. The cut of a diamond will greatly affect its appearance; you can have the most perfect diamond available but if it is not cut right, it will look like a piece of glass. Because of the importance of the cut, it is also possible to obtain a diamond which may not be flawless but will look so once it has been cut and polished.

When cutting a diamond, the diamond master will take into consideration many factors such as symmetry, polish, the percentage of the Table, the depth of the Pavilion, the size of the Girdle and the Culet. The cut will also depend on the shape of the rough stone, and the desired end result. When a diamond is cut, it will generally lose about 50% of its mass.

It’s worth noting that Cut grades are not a universal system; each jeweler can use its own type of grading system. A diamond retailer will usually stick to the GIA chart referenced here, but a retailer may assign any term they choose. To avoid misrepresentation most reputable jewelers will use the GIA (Gemological Institute of America) chart.

Diamond Structure

Today’s diamonds come in many shapes and sizes, but they all have five structural elements that they have in common. These five elements create the fire and sparkle you see when light strikes its surface. The five elements are :

This is the largest surface of the diamond, the flat top. As light enters the Table it is refracted down, and then in turn is reflected back up from the pavilion. When observed with the human eye, the Table is where most of the light or sparkle comes from.

When producing measurements to cut a diamond the table percentage must be perfect. If the Table is cut too small or too large it will negatively affect the sparkle of the diamond.

When producing a grade for the Table the percentage is calculated on the size divided by the diameter of the Girdle. If a stone has a 40% Table, the Table is 40% as wide as the outline of the stone.

The angled facets which sit above the Girdle is the Crown. As with the Table, light will pass through the Crown facets, and then reflect back upwards to the observer. Because of the way the facets are cut, the Crown will disperse the light in different directions giving the diamond its sparkle.

The Crown angle is the distance measured between the Girdle and the top of the diamond. By most standards, the ideal crown height is from 14.5 to 16 percent.

The Girdle is the widest part of the stone. When placed in a typical prong type setting you can see the girdle as opposed to a bevel setting which will hide the girdle. A girdle can be too thick or too thin, which will affect the cut grade of the diamond when it is certified.

A properly cut Girdle is important for several reasons; if the Girdle is extremely thin it can easily be chipped or broken if not set in a bezel type setting. If a Girdle is too thick it usually indicates a poor cut and can even cause a grey reflection. A too thick or too thin Girdle will also affect the optics of the stone, causing light to reflect poorly.

The angled area of the diamond found beneath the Girdle is called the Pavilion; this is where most of the weight of the stone is located. As with the Gridle, the angles of the Pavilion will affect the cut grade of the stone.

The pavilion of a diamond needs to be just right; too deep or too shallow and you will have a dark or shadow affect because light is not reflecting properly. A pavilion which is too shallow can also cause an effect that is known as a “fish eye” when viewed from above. The correct angle for the pavilion is from 42.5% to 43.5%.

The Culet is the pointed end of the diamond under the Pavilion. In some cases, a facet is added making the Culet flat, or parallel to the Table. This can be left unpolished or polished. A diamond with the smallest Culet is desirable as it displays more brilliance.

If a culet is too large it can be visible when viewed through the Table; it will also allow light leakage producing a dark shadow.

Depth Percentage

When calculating the total depth percentage of a diamond one is expressing a quantity as a percentage of another; in the case of diamonds it is the depth from the Table to the Culet, expressed as a percentage of the stones Girdle diameter. The grading system for depth percentage range from Excellent to Poor.

Since each shape is different the total depth percentage will vary however, the various shapes will follow similar rules. Below are percentages for the round shape:

Excellent – 60.1% through 62%

Good – 62% through 64%

Fair – 64% - 66%

Poor – under 60% or over 66%

In the case of “fancy” shapes like the emerald, Asscher or marquise 70% through 75% may be acceptable.

This all depends on how the stone looks to its buyer; you may have a stone that is out of the normal acceptable ranges but you just love the way it looks. In a case like this it may be more about what you like than what will make a good resale value. It’s important to note that the overall grade of the cut of the diamond is much more important than each individual number on the report, as the cut is the most difficult and technically complex to determine.

Diamond Fluorescence

Diamond fluorescence is a natural occurrence, when trace minerals in a diamond react under an ultraviolet light. Approximately 30% of all diamonds will emit a soft blue (or in some cases yellow) glow, from faint to strong. It’s important to note that in normal lighting conditions this glow is not visible, but some do consider it a defect. However, if a diamond does produce the blue fluorescence it can cause the diamond to appear whiter, which could be a bonus in lower color graded diamonds.

The strength of the fluorescence is important when choosing a diamond; too strong and the stone can appear to have a film of oil, even under normal light. In some rare cases diamonds with slight blue fluorescence will be priced higher because the blue glow make the diamond appear whiter or colorless.  

Certificates and Grading

One of the most important items to walk away with after a diamond purchase is a certificate or report listing the diamond attributes. No one will insure your diamond against theft or loss without a certificate, and many insurers will accept only a certificate from the GIA, or Gemological Institute of America. The GIA was founded in 1931 and is the foremost authority on diamonds. The GIA is a nonprofit institute which offers programs on diamond and gemstone education. They are also leaders in gemological research, and have brought many new technologies to the diamond industry such as the first gemological microscope, false gem detection, and the GIA grading system which is used worldwide.

The price of a diamond will differ significantly based on small differences, often not visible to the naked eye. A diamond certificate, or diamond report, is a diamond blueprint and will contain information about the stone such as carat weight, measurements, and grades for the color, clarity, and cut. A certificate will also give piece of mind in that you can be assured your diamond is in fact a natural stone (not synthetic), and it will also list if the diamond has been chemically treated to increase clarity or minimize color.

A diamond that has been certified by the GIA will have gone through rigorous inspections by multiple diamond masters. The GIA developed the International Diamond Grading System, and merchants around the world have come to rely on their accuracy and their impartial grading. Every diamond retailer knows that providing a report generated by the GIA will lend them instant credibility.

A GIA diamond grading report will contain the evaluation of the four C’s; Cut, Color, Clarity and Carat weight, as well as a diagram of the diamond characteristics (where inclusions or blemishes may be found), and a graphic showing the diamonds proportions. You will also see the GIA grading system in the report for use as comparison. For the round brilliant shape, the report will include the GIA cut grade. Security features such as watermarks, a barcode, a hologram, sheet numbering, microprinting and security screens, and even a laser engraved serial number provide peace of mind when obtaining a diamond certified by the GIA.

While there are other laboratories which will certify diamonds, such as the American Gem Society (AGS) and HRD, none are more respected than the GIA. There are some retailers that have managed to pressure laboratories into lowering their standards, which allows them to sell inferior diamonds as more valuable. Before accepting a diamond report be sure your familiar with the laboratory that has produced it. Diamonds which have been certified by labs such as the International Gemological Institute (IGI) or the European Gemological Laboratory (EGL) can be found at discount prices, but this is because the standards at these laboratories are not a rigorous as those found at GIA. Because of this, most insurers will not accept certificates from the IGI or EGL for insurance purposes.