Diamond testing
Diamond testing

Diamond 101

No 2 diamonds are exactly the same!

Diamonds are usually graded by 3 different experts. The inclusions and blemishes in the diamond are the same; however, the opinions of the experts on the grade of the diamond vary slightly.

The 4 C’s

Gold Buyer Wellington
Diamond and diamond jewelry buyers
  1.       Carat Weight

A unit of weight (CT) used to measure diamonds. Carat equals 0.2 grams or 200 miligrams, about the weight of a paper clip. Carat is different from Karat; one is for the weight of a diamond, the other to the purity of gold.

A higher carat means a rarer and bigger size diamond. The costs of diamonds vary by size; the higher the carat the greater the cost per Carat will be. The prices of diamonds greatly increase at the full and half Carat weight. Carat weight is not a good representation of a diamond’s size. People usually judge diamond size by the surface area on the top because this is how we view a diamond  when it is in its setting.

Comparing 2 diamonds of equal Carat can have very different prices depending on the other 4 C’s of a diamond, Clarity, Color, and Cut.

The measurement Carat originated from the carob seeds that were used to balance scales.

A diamond below one Carat is described using “points.” For example, a diamond weighing .Carats will be described as a “fifty pointer.” Any diamond weighing over 1 Carat is described using decimals, such as one point o’ five carats for a 1.05 CT diamond.

Choosing the right Carat weight depends on a variety of factors. An important factor is the size of “her” hand. The smaller “her” finger is, the larger the diamond looks.

Because larger diamonds are rarer, you will typically not only pay more in total, but price per carat as well. Less than one in one million rough stones mined are large enough to produce a finished 1 carat diamond.

Two diamonds of the same shape and carat weight may still appear different in size based on the cut proportions. A deeply cut diamond has a greater proportion of its total weight “hidden” in the depth, resulting in a smaller diameter than a well cut diamond. These differences are usually small, but noticeable. A well cut diamond may even have a slightly lower carat weight than a deeply cut diamond, yet still have a larger diameter, making it appear larger in size.

Cutter of rough diamond has to balance optimal cut and maximum yield (cutting the diamond to maintain as much carat weight from the rough stone as possible). Many people are willing to pay more for larger diamonds that are fair-cut than smaller well cut diamonds. there are at times pressure on the cutter to sacrifice appearance for weight. Cut is important because of this.

Two diamonds of equal carat weight may also appear very different in size based on the shape of the diamond. For instance, a 1 carat marquise tends to appear larger than a 1 carat round. The chart below illustrates why. For each diamond, the chart shows the following:

  • Approximate size. The diamond images shown are a very close approximation of the actual size of a 1 carat excellent cut for each shape. Visually, the longer shapes (oval, marquise, pear, emerald) tend to appear larger to the eye than the round and square shapes.
  • Measurements (Length x Width). The measurements correspond to the shape shown above, and are typical for excellent cut diamonds of 1 carat weight.
  • Crown Area – The total surface area (mm2). The area gives the true size of the diamond face up (as it would appear when set in a ring). For example, while the oval diamond image appears larger than the round image, the actual surface area is the same for the two shapes, meaning the difference in size is one of perception, not reality. In contrast, the oval not only appears larger than the princess cut, it actually has a larger surface area (approximately 10% larger in this example), meaning the difference is not simply an illusion created by the elongated shape.
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  1.    Clarity

Clarity refers to the amount and size of the flaws (inclusions and blemishes) in a diamond. Clarity is thought to have the least impact on a diamond’s appearance from the 4 C’s.

Diamonds with less imperfections have higher grades than those with more imperfections.

Diamonds are formed when carbon is exposed to extreme heat and pressure deep within the earth, and because of this process, almost every diamond has flaws. These flaws are known as “inclusions” and “blemishes.” Inclusion – found inside the diamond. Inclusions include bubbles, cracks, and non-diamond minerals. Blemishes-found on the surface of the diamond.


Inclusions affect the clarity of a diamond by interfering with the passing light making the stone less brilliant. Some inclusions can affect the strength of a diamond and in some cases make it more likely that the diamond will shatter.

Pinpoint Inclusions: Small light or dark crystals that appear in diamonds. They can be found by themselves or in clusters and a large cluster of pinpoint inclusions create a hazy spot in the diamond known as a cloud.

Laser Lines: Laser lines occur when an inclusion is removed from a diamond using a laser. They leave a vapor like trail from the surface of the diamond up to the point where the inclusion was within the diamond. They are an unnatural inclusion.

Feathers: Cracks within the diamond that resembles the shape of a feather. If a feather crack touches the surface of a diamond, the diamond is more prone to cracking due to the top of the diamond receiving more accidental blows.

Cleavage: A straight crack inside the diamond with no feathering. A cleavage crack can split the diamond apart if it is hit from the correct angle.

Girdle Fringes/Bearding: Hair like lines that appear around the girdle (Where the top/crown and bottom/pavilion of the stone meet). If there are too many girdle fringes/bearding, it can be polished away or removed by re-cutting the diamond.

Grain Lines/Growth Lines: Lines within a diamond that occurs by irregular crystallization.


There are many blemishes that barely have any effect on the diamond’s appearance. Blemishes occur when a diamond is cut and polished, while it is being worn, or they are a natural part of the diamond.

Scratch: A fine surface line that can be removed by polishing.

Abrasion: Occurs when diamonds rub against each other from people’s mishandling of jewelry. A series of nicks on the edges of the facet. Causes the facet to appear fuzzy.

Pit: Occur when a pinpoint inclusion

Diamond Plot

What fingerprints are to each and every unique person, a diamond plot is to a diamond. The diamond plot is what jewelers use to see how many blemishes, and inclusions a diamond has. The less marks on a diamond plot the better quality the diamond is. The diamond plot gives you a picture of the diamond as if you were hovering over the top face, a top-down view. All of the inclusions and blemishes that you may or may not be able to see with the naked eye is shown on the diamond plot. When comparing the markings on the diamond plot to the diamond, some of the markings will be impossible to see unless seen from the side angle.

Diamond Clarity Chart

  • FL –Flawless: No inclusions or blemishes. Very rare.
  • IF – Internally Flawless: No inclusions, only blemishes. Very rare.
  • VVS1, VVS2 – Very, Very Slightly Included: Inclusions cannot be seen with the naked eye and are difficult to see even with 10x magnification.
  • VVS1 – Inclusions are usually seen from the pavilion (bottom) of the diamond.
  • VVS2 – Inclusions are usually seen from the crown (top) of the diamond.
  • VS1, VS2 –Very Slightly Included: Inclusions and Blemishes are visible with 10x magnification but almost impossible to detect with the naked eye.
  • SI1, SI2 – Slightly Included: Inclusions and blemishes are visible with 10x magnification and may be seen with the naked eye.
  • SI1– lowest diamond grade with inclusions that are hard to see with the naked eye
  • SI2– Inclusions can be seen with the naked eye if a person knows what they are looking for.
  • I1– Included: Inclusions are visible to the naked eye
  • I2, I3 – Included: These diamonds contain inclusions that are so pronounced, many diamond dealers do not carry them.
  1.       Color

The color of a diamond does NOT change over time. The scale to grade a diamond’s lack of color goes from D-Z with D being the clearest. The further down the scale you go, the more yellowish tint the diamond has. Diamonds higher in the range are more valuable. The yellowish tint is formed from the presence of nitrogen.

  • Chemically pure and structurally perfect diamond is transparent with no hue or color
  • Almost no diamond is perfect
  • Chemical impurities affect color
  • The hue and intensity can either take away or add value
  • Can come in variety of colors, depending on structural defects, which cause coloration
  • Diamonds that are intense yellow, brown, or any other color are considered fancy color diamonds

GIA color grading

  • D- colorless. Very rare.
  • E,F –colorless. Traces of color can be detected. F has a very faint yellowish tint to it that can only be seen when the diamond is viewed facedown.
  • G,H,I- near colorless. If compared with a higher quality diamond, one can see the difference.
  • N,O,P,Q,R very light yellow
  • S,T,U,V,W,X,Y,Z are light yellow
  1.       Cut

diamond cut has three primary effects on appearance: brilliance (the brightness created by the combination of all the white light reflections from the surface and the inside of a polished diamond), fire (the dispersion of light into the colours of the visible spectrum, seen as flashes of colour), and scintillation (the flashes of light and dark, or sparkle, when a diamond or light source is moved). In other words, a diamond with a poor cut will appear dull, even if it has the perfect colour and clarity.

The way a diamond is cut determines its cut grade. The cut is what allows for the maximum amount of light to be returned out from the top of the diamond. A well cut diamond will appear larger due to the light that is being reflected out from its top. When a diamond is poorly cut, its weight could be based at the bottom making the diamond seem smaller than what the Carat weight suggests.

Diamond Shapes

  1. Round: Most popular of all shapes. It’s designed to produce the most sparkle. It is the most researched and analyzed cut. It is a timeless cut. About 75% of all diamonds sold are round. Most round diamonds are brilliant cut, which means they have 58 facets. Cost more per carat than fancy shapes for two reasons: demand is high and it has a low yield. Most of the rough stone is lost when cutting it. “A typical round diamond (for example; a 1.00 carat, F-color, VS2-clarity, Ex cut) may cost 25-35% more than a similar fancy shape.” In 1919, Marcel Tolkowsky’s thesis “Diamond Design: A study of the reflecton and refraction of light in diamond” was released. It caused the round diamond torise in popularity. The thesis described ideal proportions of round cut diamonds to maximize brilliance, (light return) and dispersion (fire). His specifications were 53% table, 59.3% depth, 34.5 crown angle, visible cutlet.
  2. Princess Cut: Has excellent sparkle and brilliance. It is a more modern cut, created in the 1960s. They normally cost less because they allow for a greater yield from the rough cut. They tend to look smaller when viewed from the top compared to other shapes with the same carat. Created in 1980 by Betzalel Ambar and Israel Itzkowitz. Out of all fancy cuts, it’s most popular, especially for engagement rings. Good choice for flexibility in working with almost any ring style, like the round cut. Slightly lower price per carat than round cuts. Due to the four sided shape, similar to a pyramid, of the princess cut, is similar to half of the octahedron rough stone. Allows two diamonds to be formed from the same rough stone with little of the rough stone being wasted. Crown surface area is 10% less than same weight round diamonds, but because corner to corner measurement is 15% greater, it creates illusion of greater size. Traditionally square, but some are rectangular. More rectangular, lower price. Length to width ratio of 1.05 or less will appear square to naked eye. If set with other diamonds, length to width of 1.05-1.08 will look square because side diamonds make illusion of greater width of center stone. Should always be set with prongs so the four corners are protected. Most likely to chip on the corners. Flaws are more likely to be by the corners because they were once close to the outer edge of the rough stone. Once the stone is set, the corners will be covered by the prongs, making the flaws nearly invisible. Avoid stones with a table % greater than depth %.
  3. Oval: It was developed in the 1960s. It is an elliptical version of the round cut. When viewed from the top, it tends to look larger than other cuts. Created by Lazare Kaplan. Modified brilliant cut. Round and oval contains similar fire and brilliance. Elongated shape creates an illusion of a larger diamond. Slender shape makes finger appear long and slimmer. Classic oval cut is 1.35-1.5 length to width ratio. Slightly thinner cut may look more appealing when diamond is with side stones. Tend to have more of a bowtie.
  4. Marquise: Similar to the oval shape, but the ends are pointed. When viewed from the top, it will look larger than almost all other cuts. Football shaped. Modified brilliant cut. derived from the Marquise of Pompadour, for whom King Louis XIV of France allegedly had a stone fashioned to resemble what he considered her perfectly shaped mouth. Largest crown surface area. Maximizes the perceived size of a diamond. The elongated shape makes the wearer’s finger appear longer and slimmer. Classic marquise cut length to width ratio is 1.75-2.15. Symmetry is very important. Two end points need to align with each other, and the left and right sides should mirror each other. Slight misalignment can cause an off kilter look in the setting. Excellent or very good symmetry is strongly recommended. It should be set with the prongs protecting the two points. Like the princess cut, the points were once closest to the outer edge of the rough stone, so flaws are more likely to be located there. The prongs that cover the points will make the flaws invisible. Points are also more prone to chipping.
  5. Pear Shaped: It is pointed at one end and round at the other. It is also known as a teardrop cut, because of its resemblance to a teardrop. This type of cut is normally used in pendants and earrings. Modified brilliant cut. Combination of round and marquise shape. Always worn with narrow end pointing toward hand of wearer. Makes fingers appear longer and slimmer. Should have excellent or very good symmetry. Pont should line up with apex of rounded end. Shoulder and wings, the upper and lower curves on both sides of the diamond, should form uniform, symmetrical curves, with no straight edges. Rounded top should look like a semi circle. It should not be narrow or squat. Sometimes, in an effort to add weight, cutters may give diamond added girth near the point or top. It gives the diamond a squared off or squatty look. It should be avoided. Classic length to width ratio is 1.4-1.7. It should also be affected by the future setting. A narrow stone is ideal for dangling earings, and a wider shaped stone is better for a solitaire ring. Contains a degree of bowtie. Should be set with prong at the point., the point was once closest to the outer edge of the rough stone, so flaws are more likely to be located there. The prongs that cover the points will make the flaws invisible. Point is also more prone to chipping.
  6. Cushion Cut: also known as the pillow cut. It is in the shape of a square or rectangle. It is also known as the old mine cut. It’s a square cut with rounded corners. Has been around for around 200 years. It was the de facto diamond shape until the early 20th century. It is prized by antique diamond dealers due to the return or light in a chunkier pattern than today’s modern cuts. It also has an enlarged culet. In the 1920’s Marcel Tolkowsky researched different cuts to refine the cushion cut. Because of him, there has been a resurgence of popularity of this particular cut. Standards for this cut vary more than other shapes and personal taste will mainly be the deciding factor on which stone to choose. Less brilliant that round cuts, but have more fire. They have three pavilion facet patterns. Ones with extra row fo facets on the pavilion are considered, but GIA, as a “modified” cushion cut. They have a crushed ice or needle like facet pattern. Classic cut is a length to width ration of 1.00. most popular is 1.1-1.2 length to width ratio.
  7. Emerald Cut: It has a recagular shape with the edges cut to have steps, which act like mirrors. The mirrors are used to show the clarity of the diamond. Created by the step cuts of pavilion and its large, open table. Produce a hall of mirrors effect, instead of the sparkle of a brilliant, with interplay of light and dark planes. Long lines and dramatic flashes give this cut an elegant appeal, the cut was originally for cutting emeralds. Inclusions are easier to see in this cut. Classic cut has length to width ratio of 1.5. if prefer square emerald, consider the asscher cut. It’s defined as a square cut emerald by GIA.
  8. Asscher Cut: it is similar to the emerald cut, but it is more octagonal. It’s corners and steps are larger and deeper. First produced in 1902 by Asscer Brothers of Holland. They cut the world’s largest rough stone, at the time, the Cullinan at 3106 carats. Peaked in popularity in 1920’s but made a comeback around 2002, due to the modifications that increased brilliance. Similar to square emerald cut. Usually has larger step facets, a higher crown, and a smaller table. Produces more brilliance than emerald cut. Well cut asscher will appear to have concentric squares as you look through the table. Has cropped corners, but because the cut is square, the cropped corners make it look somewhat octagonal. When mounted in a four prong setting, it maintains its unique shape within a square silhouette. Classic cut has length to width ratio of 1.00. a ratio of 1.05 or less will seem square to the naked eye.
  9. Radiant Cut: Corners are angled and rectangular. Similar to princess cut, but not as square. First developed In the 1970s. first square cut to have complete brilliant cut facet pattern applied ot crown and pavilion. It creates a vibrant, lively square diamond. Popular in 1980’s. cropped corners fo square is nice middle ground between cushion and princess cut. Looks good when set with round or square cornered diamonds. In longer, or more rectangle, cuts, a bow tie effect is more likely to appear. A ratio of 1.0-1.05 will appear square to naked eye. Rectangular cut is ideal for those who like emerald cut, but want the brilliance of a round stone. Looks very similar to princess cut, but it has cropped corners. Once set, they look nearly identical due to prongs covering the corners.
  10. Heart Shaped: shaped like a heart. Modified brilliant cut. Unique and unmistakable symbol of love. Popular in solitaire pendants and rings. Symmetry is very important. It’s critical that two halves of heart are identical. Cleft, which is between the two lobes, should be sharp and distinct. The wings, as they curve to the point, should have a very slight rounded shape. Ones less than .50 carats may not be a good choice, becuas it’s more difficult to perceive in smaller diamonds, especially after it is set in the prongs. for smaller hearts, a bezel or three pong setting will preserve the outline of the shape after it’s set. The prongs should be placed one on each lobe, and one on the point. Come in variety of silhouets, from fat to narrow, but it should be chosen based off of personal preference. Classic length to width ratio is 1.00. Ones for pendants should be more narrow, 1.05-1.15 length to width ratio. Ones in solitaire rings should me more wide, .85-1.00.

Depth %: refers to distance between culet and table when diamond is viewed from the side. expressed in millimeters. it’s calculated by dividing the depth by the width of the diamond. the lower the depth %, the larger a diamond of a certain carat will appear.

table %: calculated by dividing with of table facet by width of diamond.

  • diamond girdle: outer edge of diamond where crown meets pavillion. May be faceted- series of tiny polished sides taht go around the diamond, bruted- single continuous unpolished surface that goes around the diamond, this type of girdle is now uncommon, or polished- a bruted girdle that has been polished to make it smooth. The way the girdle is does not affect the price or appearance of the diamond. it is described by width. the width varies at different points of the diamond. and is described as a range, from thinnest to the thickest point. can impact diamond in three ways: The thickness of the girdle affects the relative position of the surrounding facets, and so can impact cut. Because girdle width is already factored into the diamond’s overall cut grade, a diamond graded as well cut will produce superior brilliance, fire, and scintillation, even if the girdle itself is not in the ideal Thin-Slightly Thick range of width.
  • A thicker girdle will add weight to a diamond, thereby increasing its price. Since a thick girdle adds depth to a diamond but not width, a thick girdled diamond will not appear any larger when viewed from the top (e.g. when set in a piece of jewelry), despite the additional carat weight. The effect on carat weight and price is minimal, but real.
  • An Extremely Thin girdle is more susceptible to chipping, and for that reason should be avoided for diamonds that are to be set in a ring. Earrings or pendants are less exposed to rough contact and so are less susceptible to chipping around the girdle. Avoid both Extremely Thin and Very Thin girdles in princess cut diamonds, as this shape already has sharp corners more prone to chipping. If you do purchase a princess cut diamond with a Very Thin girdle, consider setting it in a style that covers and protects the corners.

Diamond culet: small area at the bottom of the pavilliion. it can be pointed or a very small facet that sits parallel to the table. Any diamond culet size of Medium or smaller will be invisible to the naked eye, and have no negative impact on a diamond’s appearance. However, if a culet is Slightly Large or larger, it may allow light entering from the crown to pass straight through the culet facet, reducing the diamond’s brilliance. This may also make the culet appear as an inclusion, or create a dead area on the diamond where the light is escaping through the bottom.

polish: degree of smoothness of each facet of a diamond;  When a diamond is cut and polished, microscopic surface defects may be created by the polishing wheel as it drags tiny dislodged crystals across the diamond’s surface. Depending on the severity, these defects may disrupt light patterns as the light rays enter and exit the diamond. polish grade of excellent to good, any polishing defects are not visible to naked eye and have no impact on overall appearance. if diamonds have clarity grade of i1 or lower, polish grade of fair is acceptable. therese diamons have internal inclusions that are visible to naked eye so the polish becomes less relevant. diamonds less than .75 carats, a plish grade of fair or better will not affect appearance to an untrained observer. Poor grade should be avoided for all diamonds.

Diamond symmetry: how precisely the facets align and intersect. can include extra or misshapen facets, off center culets and tables, and wavy girdles. poor symmetry may misdirect light sending it off at the wrong angles, which reduces the brilliance. Often, a diamond cutter will purposefully allow a minor reduction in symmetry as a way of preventing a defect present in the rough stone from being retained as part of the finished diamond. it’s important in diamonds of vvs2 clarity and higher. the subtle defects would compromise the flawless appearance. has a significant impact on price; a diamond with Excellent Symmetry and polish may be priced 10%-15% higher than a diamond with Good Symmetry and Polish. This premium has more to do with consumer’s perceived value of “excellent” grades, than the actual effect on a diamond’s appearance. Because diamonds with Poor symmetry have defects visible to the naked eye, these diamonds should be avoided in all cases

Cut refers to diamonds proportions, symmetry, and polish, not it’s shape.

When light strikes a diamond, approximately 20% immediately reflects off the surface (as glare). Of the 80% that enters, a portion will escape through the bottom of the diamond (where the observer cannot appreciate it). A well proportioned diamond will have each facet properly placed and angled so as to maximize the amount of light that reflects back out of the crown (top) of the diamond, to the eye of the observer. This reflected light is perceived as scintillation, fire and brilliance.

Watch out for: Inclusion is visible to the naked eye; extremely thick girdle; fair or poor symmetry; strong fluorescence; diamonds without a GIA certification

Comparison between Carat weight and Surface Area

  • When reviewing any diamond, it is important to remember that an increase in diameter will have a larger increase in the crown surface area which results in a perceived increase in overall size.
  • Two diamonds with the same shape and carat size can be perceived as having different sizes due to the cut dimensions. A diamond with a deep cut has more of it’s weight “hidden” in the depth, which results in a smaller diameter than a well cut diamond.
  • A well cut diamond that has a slightly lower carat weight than a deeply cut diamond, yet has a larger diameter will appear larger in size.
  • A diamonds cut and carat determine how big the stone will look. A well cut diamond that is lighter than a poorly cut diamond will appear to be bigger diamond that is more beautiful than the heavier one.
  • A carat is based on weight. It does not reflect that actual size of a diamond. It should be considered with the diameter in millimeters and its cut grade.
  • The weight of a poorly cut diamond can be hidden in the base of the diamond. That will make the diamond appear smaller in size.

Irradiated/Fancy Diamonds

Colored diamonds are very rare and expensive. To provide the public with the sought after colored diamonds, jewelers put the diamond through a process of high radiation treatments. The diamond then gets its color after both the radiation treatments are complete and the heating process.

When repairing diamonds, the jeweler has to re-expose the diamond to intense heat. This can cause the color of the diamond to change as the process to add color to a diamond is not full proof.

When evaluating fancy diamonds, the clarity section is less important because the inclusions tend to be masked by the color of the diamond.

When cutting a fancy diamond, instead of cutting the diamond to maximize sparkle, the diamond is cut in whichever way will emphasize the color

Every colored diamond has been irradiated because it has been exposed to natural radiation.

  • Red-
  • Blue- color caused by presence of boron
  • Yellow- color caused by presence of nitrogen
  • Green- color caused by natural radiation

Diamond Terms

  • Table/Face – The flat top of a cut stone
  • Girdle – Where the top/crown and bottom/pavilion of a diamond meet. The area that is usually grasped by prongs when picking up a diamond.
  • Crown – The top part of the diamond that is above the girdle
  • Pavilion – The bottom part of the diamond that is below the girdle.
  • Inclusions – Flaws found inside a diamond.
  • Blemishes – Flaws found on the surface of a diamond.

Diamond Fun Facts:

  • The birthstone of the month of April is a diamond
  • The hardest natural substance on Earth is a diamond
  • Diamonds are colorless when in their pure state
  • The most common colors of a diamond is yellow and brown
  • The rarest colors of a diamond are blue and red
  • 1 Carat – 0.2 grams or 0.007 ounces
  • India is where diamonds were first discovered
  • A diamonds melting point is 3820K or 6420F / 3547C
  • A diamonds boiling point is 5100K or 8720F / 4827C
  • In ancient times diamonds were worn because they were believed to bring about strength, courage, and invincibility
  • The word diamond is derived from the Greek word “adamas” which means unbreakable
  • The Greeks and Romans believed diamonds were the tears of the gods and splinters of fallen stars
  • Diamonds can only be scratched by other diamonds
  • 250 tons of ore must be mined and processed to produce a single one carat diamond
  • Diamonds are the best known, naturally occurring, thermal/heat conductor

    Diamond through a jewelers loop
    Diamond through a jewelers loop

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