The Foundry Journal

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The Foundry Journal

The 4Cs of Diamond Grading

July 14, 2015

In the News

Style Guide

The 4Cs of Diamond Grading

July 14, 2015

Diamond Industry

The 4Cs of Diamond Grading

July 14, 2015 BY Alon Ben-Shoshan IN Style Guide

Until the middle of the twentieth century, there was no agreed-upon standard by which diamonds could be judged. GIA created the first, and now globally accepted standard for describing diamonds by: Color, Clarity, Cut, and Carat Weight. Today, the 4Cs of diamond quality is the universal method for assessing the quality of any diamond, anywhere in the world.

Carat

Carat is a measure of a diamond’s weight. A metric “carat” is defined as 200 milligrams. The word carat came from Italian carato, which came from kerátion (κεράτιον) meaning carob seed. Supposedly, carob seeds had unusually low variability in mass, making them a good tool for measuring out small amounts of weight.

Each carat (written 1.00ct) can be subdivided into 100 ‘points’. This allows very precise measurements to the hundredth decimal place. A jeweller may describe the weight of a diamond below one carat by its ‘points’ alone. For instance, the jeweller may refer to a diamond that weighs 0.25 carats as a ‘twenty-five pointer.’

Color

Diamond is pure carbon in its “tetrahedral” crystallographic shape. In this form, the diamond carbon crystal is transparent to all visible light.

Whether mined or grown, colorless diamonds are very rare. The closer the diamond is to colorless the higher it is evaluated. The most rare and white ones are graded with “colorless” (D, E, F) or “near colorless” (G, H, I, J). Diamonds of colors D and E are not commonly provided by Diamond Foundry as their whiteness grade difference relative to F through H is barely perceptible to non-gemologists yet their price is far higher.

One advantage of diamonds that come from Diamond Foundry is that the tint color in the “K-L-M” range is a platinum tint and not a yellow/brown tint as with mined diamonds.

Many of these color distinctions are so subtle that they are invisible to the untrained eye – however, these distinctions can make a very big difference in price.

Clarity

Clarity refers to how “clean” the diamond looks, both internally, and externally. The subtle differences between clarity grades can be quite difficult to discern as a non-gemologist. As a general rule, if you cannot see any inclusions with the naked eye, then the diamond is likely SI or better. In order to determine clarity, jewelers use a “loupe” that provides 10x magnification. VS inclusions are very hard to see even under this magnification. Diamonds with no inclusions visible, even under 10x magnification, are called Internally Flawless (IF). They are incredibly rare and therefore much more expensive per carat.

Diamond clarity

Internal inclusions that can be found in the diamond include: clouds, feathers, included crystals or minerals, and knots. Blemishes that are found on the surface of the diamond include: polish lines, scratches, nicks, pits, and chips.

Cut

Cut is sometimes used to refer to the diamond’s shape. The cut grade specifically refers to the proportions and arrangement of the facets on a diamond. The precision of a diamond’s faceting is crucial to light performance, as it determines the way light behaves inside a diamond and then exits the diamond to meet your eye.

  • Brilliance is the total light reflected from a diamond.
  • Fire describes the dispersion of light into the colors of the spectrum.
  • Scintillation describes the flashes of light, or sparkle, when a diamond is moved.

In a diamond cut to exact proportions, light is reflected from one facet to the next and then dispersed through the upper part of the stone. If the diamond is too deep, then the light does not reflect back to the top, but escapes out the other side. If the diamond is too shallow, then the light escapes through the bottom before it can be reflected.
How is the grade of cut determined? Cut is a combination of each stone’s proportions, measurements, angles, faceting accuracy and polish. Any modern polishing factory today has a small 3D scanner which can accurately measure all of the diamond’s facet angles and dimensions. This data can provide an un-biased cut-grade for – excellent, very good, good, fair, and poor.

For fancy shape diamonds (everything but round is called fancy shape) there are no measurements, angles or relationships that determine cut grade. Non-round stones have grades for symmetry and polish only. There are literally thousands of combinations a cutter could choose in cutting a fancy shape diamond so they vary wildly in the way they ‘face up’.

A rough diamond being polished on a scaife.

Diamond cutters in past centuries used techniques that are no longer common today. They often cut diamonds by hand, giving them shapes and dimensions that capture the character and essence of their eras. Diamonds cut using the old techniques may exhibit slightly more fire and less brilliance. They are sometimes preferred for their romantic look. In recent times, antique diamond cuts have enjoyed a renewed popularity.

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