How to test the quality of your diamond?

How to test the quality of the diamond?

One of the first things most people learn about diamonds is that not all diamonds are created equal. In fact, every diamond is unique. Diamonds come in many sizes, shapes, colors, and various internal characteristics.

All polished diamonds are valuable. That value is based on a combination of factors. Rarity is one of those factors. Diamonds with certain qualities are rarer—and more valuable—than diamonds that lack them.

Jewelry professionals use a systematic way to evaluate and discuss these factors. Otherwise, there would be no way to compare one diamond to another. And there would be no way to evaluate and discuss the qualities of an individual diamond. Diamond professionals use the grading system developed by GIA in the 1950s, which established the use of four important factors to describe and classify diamonds: Clarity, Color, Cut, and Carat Weight.

These are known as the 4Cs. When used together, they describe the quality of a finished diamond. The value of a finished diamond is based on this combination.

A diamond’s value is often affected by the rarity of one or more of the 4Cs. Colorless diamonds are scarce—most diamonds have tints of yellow or brown. So a colorless diamond rates higher on the color grading scale than a diamond that is light yellow. Value and rarity are related: In this case, a colorless diamond is rarer and more valuable than one with a slight yellow color. The same relationship between rarity and value exists for clarity, cut, and carat weight.

The 4Cs describe the individual qualities of a diamond, and the value of an individual diamond is based on these qualities. The terms that people use to discuss the 4Cs have become part of an international language that jewelry professionals can use to describe and evaluate individual diamonds.

Today, the descriptions of each of the 4Cs are more precise than those applied to almost any other consumer product. And they have a long history. Three of the—color, clarity, and carat weight—were the basis for the first diamond grading system established in India over 2,000 years ago.


Subtle differences in color can dramatically affect diamond value. Two diamonds of the same clarity, weight, and cut can differ in value based on color alone. Even the slightest hint of color can make a dramatic difference in value. Diamonds come in many colors. Diamonds that range from colorless to light yellow and brown fall within the normal color range. Within that range, colorless diamonds are the rarest, so they’re the most valuable. They set the standard for grading and pricing other diamonds in the normal color range.

GIA's D-to-Z color-grading scale is the industry's most widely accepted grading system. The scale begins with the letter D, representing colorless, and continues, with increasing presence of color, to the letter Z.


Few things in nature are absolutely perfect. This is as true of diamonds as anything else. Diamonds have internal features, called inclusions, and surface irregularities called blemishes. Together, they’re called clarity characteristics. Clarity is the relative absence of inclusions and blemishes.

Among other things, blemishes include scratches and nicks on a diamond’s surface. Inclusions are generally on the inside, and some might break the surface of the stone. Sometimes, tiny diamonds or other mineral crystals are trapped inside a diamond when it forms. Depending on where they’re located, they might remain after the stone has been cut and polished, and they can affect a diamond’s appearance.

Clarity characteristics might have a negative influence on a diamond’s value, but they can have positive effects as well. For one thing, they help gemologists separate diamonds from imitations. (This is easier with included diamonds than with flawless ones.) And because no two diamonds have exactly the same inclusions, they can help identify individual stones. They can also provide scientists with valuable information about how diamonds form.


A beautifully finished diamond is dazzling, with every facet displaying the craftsman’s skill and care. When a diamond interacts with light, every angle and every facet affects the amount of light returned to the eye. This is what gives it its face-up appearance.

Diamonds are renowned for their ability to transmit light and sparkle so intensely. We often think of a diamond's cut as shape (round, emerald, pear), but a diamond's cut grade is really about how well a diamond's facets interact with light.

Precise artistry and workmanship are required to fashion a stone so its proportions, symmetry and polish deliver the magnificent return of light only possible in a diamond. The quality of the cut is crucial to the diamond's final beauty and value. And of all the 4Cs, it is the most complex and technically difficult to analyze.

The GIA Cut Grading System for the standard round brilliant diamond evaluates seven components. The first three, brightness, fire, and scintillation, consider the diamond's overall face-up appearance. The remaining four, weight ratio, durability, polish, and symmetry, assess a diamond's design and craftsmanship.

BRIGHTNESS Internal and external white light reflected from a diamond.

FIRE The scattering of white light into all the colors of the rainbow.

SCINTILLATION The sparkle a diamond produces, and the pattern of light and dark areas caused by reflections within the diamond.

As a general rule, the higher the cut grade, the brighter the diamond. Under fluorescent lighting, these diamonds (left to right) display high, moderate, and low brightness. The term “cut” also can describe a fashioned diamond’s shape. Shapes other than the standard round brilliant are called fancy cuts. They’re sometimes called fancy shapes or fancies. Fancy shapes also have names of their own, based on their shapes. The best known are the marquise, princess, pear, oval, heart, and emerald cut.


Many goods are sold by weight—by the kilogram, ounce, pound, or ton. Even people who have never bought a diamond are used to the idea that weight and price are related. They understand that a larger diamond is probably more valuable than a smaller one. But there are two things that often surprise people when they start learning about diamonds and carat weight.

The first is the precision with which diamonds are weighed. Diamond weights are stated in metric carats, abbreviated “ct.” One metric carat is two-tenths (0.2) of a gram—just over seven thousandths (0.007) of an ounce. One ounce contains almost 142 carats. A small paper clip weighs about a carat.

The metric carat is divided into 100 points. A point is one-hundredth of a carat. Diamonds are weighed to a thousandth (0.001) of a carat and then rounded to the nearest hundredth, or point. Fractions of a carat can mean price differences of hundreds—even thousands—of dollars, depending on diamond quality.

Over a carat, diamond weights are usually expressed in carats and decimals. A 1.03-carat stone, for example, would be described as “one point oh three carats,” or “one oh three.” Weights for diamonds that weigh under a carat are usually stated in points. A diamond that weighs 0.83 carats is said to weigh “eighty-three points,” or called an “eighty-three pointer.”

Carat weight can also be symbolic. While the visual difference between a 0.98-carat diamond and a 1.01-carat diamond is negligible, many people will opt for the larger stone—even at a much higher price. Some weights are considered “magic sizes”: a half-carat, three-quarter carat, one carat, etc. There’s not much difference in their weights, but if both are D-color round brilliants with identical clarity and cut, the size makes all the difference. They really don’t look much different, but if a consumer’s heart is set on the one-carat size, the difference is enormous. The fact that the second stone is slightly over the “magic” one-carat size can give it as much as a 20 percent difference in price with only a 6-point difference in weight.