Diamond Basics

Shape

Monday, March 3rd, 2008

Diamonds come in a variety of shapes: round (also called brilliant), princess, Asscher, marquise, radiant, emerald, baguette, oval, heart, pear, cushion, etc.

Diamond shapes

Shape is one factor in a diamond’s price. Some shapes are more difficult to produce than others. Part of the rough diamond is wasted when cutting and polishing diamond stones.

The round (also known as “brilliant”) is by far the most popular diamond shape, accounting for more than 75% of all diamonds sold. Consumer tastes vary with fashion, often driven by celebrities or T.V. shows, but most people want their diamonds to be classics—outlasting fads or shifting fashions. Our post “Advice on picking a diamond shape” can help you determine what diamond shape your lady may prefer.

  • Princess cut (also known as “square modified brilliant”) – the second most popular shape, which accentuates diamond’s “fire” and brilliance rather than its luster. The Princess cuts are typically less expensive per carat than round brilliants because cutters do not have to cut off as much material from the rough diamond.
  • Emerald – this is a rectangular shaped diamond with a larger, open ‘table’ (‘table’ is the top of a diamond). Because of the large square of the table, the color of this diamond is more noticeable and hence should be chosen more carefully. Typically, anything in the range of K to Z grade will be visibly too yellowish.
  • Asscher – This 72-faceted diamond was designed in 1902 by Joseph Asscher, a diamond jeweler from Amsterdam. The Asscher is a square version of the rectangular emerald cut. This shape has regained some of its popularity in recent years, thanks to being featured on Sex and the City and by some celebrities.
  • Marquise (also known as “navette” or “little boat” in French) – this diamond, shaped like the hull of a boat. Marquise diamond shape makes the diamond look bigger than it actually is and also makes fingers wearing this diamond look longer and more slender. When buying the diamond of this shape, watch out for the “bow tie” effect (i.e. the diamond’s markedly dark center) if it is cut too thin. The depth of this diamond should not be less than 60%.

Read more about other diamond parameters

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Carat

Sunday, March 2nd, 2008

Finding rough diamonds is increasingly rare with size: for every million pieces of rough material only one piece on average is large enough to produce a 1-carat finished diamond. During the cutting process, a diamond typically loses 40% to 60% of its original rough diamond size. As carat weight gets larger, the value of the diamond stone increases disproportionately.

A regression analysis of available diamonds shows carat weight accounts for the biggest portion of the diamond value, followed by color and clarity. Still, a poorly crafted large diamond can be worthless compared to a much smaller, well crafted stone.

Carat Weight

Diamond prices typically increase at a higher rate from one weight / price bracket to the next. For example, price per carat for diamonds in the size bracket 1.00–1.49 carats could be $8,000, while price per carat in the bracket 1.49–1.99 carats can jump to $11,000.

In a graph below you can see how fast the price per carat jumps with diamond weight moving from one carat weight bracket to another.

Diamond Prices Depending on the Carat Weight Bracket

Diamond Prices Depending on the Carat Weight Bracket

To maximize the size of the purchased diamond without having to pay a higher price per carat, it is therefore better to buy diamonds with the size towards the higher end of a chosen price bracket:

For example, buy a diamond the size of 1.48, rather than 1.51 because the size of these stones would most likely be priced according to different price brackets. Thus, 1.48 carat diamond would be priced at 1.48 x $8,000 = $11,840 while 1.51 carat diamond would be priced at $11,000 per carat and thus would have the value of 1.51 x $11,000 = $16,600, that is $5,000 more for just 0.02 additional carats.

Etymology of the Word “Carat”

“Carat” is just a diamond industry special word for weight of a diamond stone. One carat is equal to 200 milligrams, or in other words, a 5-carat stone weighs 1 gram. The word “carat” originates from the Greek word kerátion, which means carob beans, which were known in the ancient world for uniformity of their size and weight and were used as a measure of weight for different objects, including gemstones.

In the Far East instead of carob beans jewelers used rice grains to determine the weight of gemstones. Because of this fact, you may occasionally hear some jewelers referring to a 1-carat diamond a “four grainer,” which means in the past 1 carat was equal to four grains of rice.

The weight of smaller diamonds is often expressed as points, not carats. One carat is equal to 100 points. Thus, for example, a 10-point diamond has the weight of 0.1 carats.

Read more about other diamond parameters

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Cut

Saturday, March 1st, 2008

The diamond cut often refers to two separate characteristics of a loose diamond: (1) its shape, and (2) its make, or style of cutting and quality, which consists of polish and symmetry.

Polish and Symmetry

A diamond’s shape as well as its polish and symmetry affect the “behavior” of the stone—simply speaking, how it reflects light. In general, a diamond’s cut is all about maximizing the optical light effects that determine the ultimate beauty of the diamond: brilliance (amount of light reflected back to viewer), fire (split of light into a rainbow’s colors), and scintillation (glittering of reflected light in the crystal and visibility of dark spots when stone is moved).

Polish and symmetry significantly impact all three of these. In the following picture you can see the most critical parts of a diamond and their names.

Cut

To ensure that the diamond has the best brilliance and fire, the best option is to stay away from stones with proportions below the ideal standard. Below you can find the explanation for all facets of a diamond and standards below which you should not buy the stone. The information about such standards can be found in the diamond certificate. GIA calls their certificates diamond dossiers or diamond grading reports while AGS calls theirs diamond quality documents or diamond quality reports.

A diamond’s most critical parts:

  1. Diameter of a loose diamond, measured at the Girdle, which is the widest portion of a stone.
  2. Girdle – the middle portion of a diamond stone, its widest part. The Girdle is measured from “extremely thin” to “extremely thick” – the “medium” thickness Girdle is preferred (you can find the information about it in the diamond certificate). Stay away from a “thin” Girdle as it is too fragile and can chip more easily, also do not buy a “thick” one either as it is unnecessarily adding weight to the stone where it matters the least.
  3. Table – the top of the diamond, whose area size ideally should be 53% to 57.5% (in a Round Brilliant) of the Girdle diameter according to the American Gemological Society (AGS) lab studies. Some jewelers say up to 64% is still acceptable. Run away from the diamond with the Table area above 64%.
  4. Depth – in a Round Brilliant, length of the stone from the surface of the Table to the bottom of its Pavilion). Depth should ideally be 58% to 63% of the stone Diameter
  5. Crown – the portion of the diamond between its girdle and its table) – the Crown angle in the well-cut diamond should be 33 to 35 degrees
  6. Pavilion – in a Round Brilliant, the cone-shaped lower part of the stone:
    1. The Pavilion Depth of the stone, according to the AGS Lab, should ideally be 42.5% to 43.5%. Pavilion Depth is a portion of the overall diamond Depth and represents the height of a diamond Pavilion or the distance from the Girdle to the bottom of Pavilion, called Culet. In diamonds with very deep Pavilions, the entire surface of the Table appears to be dark creating what industry experts call a “Nailhead”. On the other hand, stones with shallow Pavilions often produce a “Fisheye” effect due to Girdle’s reflection in the diamond’s Table. So, if the Certificate specifies the Pavilion Depth is above 43.5% or below 42.5% – the diamond’s sparkle will be diminished.
    2. Pavilion angle is another important dimension of the stone, which determines its brilliance and fire. However, many GIA certificates (called Diamond Dossiers and Reports) do not provide information on the diamond’s Pavilion angle. So, you will have to rely on the information on the stone’s overall quality of the Polish and Symmetry as well its Table size and Depth (all GIA Dossiers and Reports provide this information as a bare minimum).
  7. Culet – the facet at the bottom tip of a gemstone. The quality of the Culet is typically specified in a diamond certificate – the preferred Culet is not visible with the unaided eye (so, the best one should be graded either “None” or “Medium”).

Culet

What impacts the brilliance and scintillation of the diamond most significantly are ratios and proportions of various dimensions in relation to each other. They determine how well (or not so well) and how much of the light is reflected inside the crystal and back to the surface through the diamond’s table. You can find this information on certificate specification enclosed with every certified loose diamond. If the diamond is not certified by one of the gemological trade associations, well, then,
The GIA (the Gemological Institute of America) grades diamonds with descriptive words Excellent, Very Good, Good, Fair, and Poor to convey the quality of the gemstones’ Cuts.

The ‘polish’ grade describes the smoothness of the diamond’s facets. The symmetry grade refers to alignment of the facets:

  • Poor polish of the diamond surface can dull the light radiating from the stone. It may also create blurred or dulled sparkle.
  • Poor symmetry can misdirect the light inside the stone as it enters and exits the diamond – the more light is lost due to poor symmetry, the less sparkly the stone would look.

Read more about other diamond parameters

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Color

Friday, February 29th, 2008

Diamonds can have different colors ranging from colorless (also called white), through yellow, blue, green, pink, orange, and to the rarest, red. The color of a diamond is determined by the chemical impurities as well as structural imperfections of the stone. Some diamond colors add to their value, often significantly. (Red diamonds are substantially more expensive than white ones—due to their rarity and natural beauty.) The least expensive are yellowish diamonds, unless the stone is a very bright yellow, making it a more valuable fancy stone.

Gemstone associations and institutes, such as GIA (the Gemological Institute of America), AGS (American Gem Society), EGL (European Gemological Laboratory), IGI (International Gemological Institute), AGA (American Gem Appraisers), etc., all have their own color grading standards and nomenclature.

The most widely used grading system was developed by the GIA. It grades diamonds from D (colorless) to M (faint yellow) all the way to Z (light yellow). Color grades beyond Z are considered to be ‘fancy’ grades and are graded separately. Such diamonds are also typically more, not less, expensive than those with the yellowish hue due to their rarity and beauty.

Diamond Color

When buying a diamond with a slightly yellow hue, tricks of the trade can help you mask some of that yellowish color. For instance, match the stone color to the setting’s metal color. Yellow metal (such as yellow gold) makes slightly yellow or brown diamonds appear more colorless, while darker yellows and browns look darker and richer. White metal makes slightly yellow or brown stones look more yellow or brown (typically in an unpleasant sort of way) but enhances the color of blue stones. So, if you go for a diamond below K-color grade (GIA grading classification), think about buying a yellow gold setting, rather than white gold or platinum.

Read more about other diamond parameters

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Clarity

Thursday, February 28th, 2008

The diamond clarity refers to the existence and visual appearance of the so-called imperfections and blemishes

  • Imperfections can be foreign material, such as other crystals, as well as air bubbles inside the diamond, or internal imperfections, such as tiny cracks inside the stone.
  • Blemishes are diamond surface imperfections (e.g. polish lines, scratches, chips, etc.).

The size, color, and dimensional orientation of imperfections and blemishes determines how visible they are to the naked eye. The grade of the clarity is assigned to each diamond based on appearance under 10x magnification.
Imperfections obstruct light refraction, making diamonds less brilliant. The larger the imperfections, the worse the diamond’s ability to reflect the light, degrading the quality of the gemstone.

The GIA (the Gemological Institute of America) has used its clarity grading scale since 1953. Diamonds are graded from FL (flawless) to I3 (imperfect), which is a stone with a lot of imperfections and blemishes visible to the naked eye.

Clarity grading scale (10x magnification)
Clarity / Flawless F / Flawless
The diamond shows no inclusions or blemishes of any sort under 10X magnification when observed by an experienced grader.
Note: Truly flawless or internally flawless (F or IF on the GIA’s grading scale) diamonds are extremely rare.
Clarity / Internally Flawless IF / Internally Flawless. The diamond has no inclusions when examined by an experienced grader using 10X magnification, but will have some minor blemishes.
Clarity / Very, Very slightly included VVS1, VVS2 / Very, Very slightly included
The diamond contains minute inclusions that are difficult even for experienced graders to see under 10X magnification.
Clarity / Very slightly included VS1, VS2 / Very slightly included
The diamond contains minute inclusions such as small crystals, clouds or feathers when observed with effort under 10X magnification.
Clarity / Slightly included SI1, SI2 / Slightly included
The diamond contains inclusions (clouds, included crystals, knots, cavities, and feathers) that are noticeable to an experienced grader under 10X magnification.
Clarity / Included I1, I2, I3 / Included
The diamond contains inclusions (possibly large feathers or large included crystals) that are obvious under 10X magnification and may affect transparency and brilliance.
Clarity / Included

In 1992 the European Gem Laboratory (EGL) introduced another grade of clarity: SI3. Ostensibly, many industry craftsmen complained there was too wide a gap between the GIA standard grades SI2 (slightly included) and the I1 (included). Hence, why not offer a SI3 grade to bridge the gap? GIA did not recognize this new grade and a lot of jewelers believed it was just a veiled attempt to price gouge the most gullible consumers by selling them I1 grade diamonds at SI2 prices.

Different diamond grading labs and agencies developed their own color and clarity systems. All grading systems rely on human judgment and ability to determine the grade based on the overall agency grade description. Oftentimes the same diamond can be graded differently by the same agency if sent for grading more than once. Some agencies are considered stricter and more precise in how they grade stones. Diamonds tested by agencies such as AGS and GIA command a premium, while comparable stones graded by such agencies as EGL, HRD, and IGI are sold at 3% to 20% less.

Read more about other diamond parameters

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