1. Color - In the chaos of extreme temperature and pressure that first created diamonds, traces of elements such as nitrogen and boron could have been incorporated into the diamond’s atomic structure. This is the source of the tincture.
The first quality grade of a diamond to be judged is its color grade. Diamond can cover the entire spectrum ofcolors but the majority of diamond colors are yellow and brown.
Diamonds are not all truly colorless, but it's the colorless diamonds, sometimes called white diamonds, which all other shades are judged against.
The Gemological Institute of America (GIA) has devised a set of guidelines to grade diamond color. The color of graded diamonds is compared to the color of control stones, preselected gems of a specific color.
A lettering system from D to Z is used to identify the amount of color present in each diamond, with D awarded only to rare, totally colorless diamonds.
D, E, F - Colorless.
G, H, I, J - Nearly colorless.
K, L, M - Faintly tinted, usually yellow.
N, O, P, Q, R - Lightly tinted, usually yellow. Tint can be seen with the naked eye.
S, T, U, V, W, X, Y, Z - Tinted, usually yellow, may progress to brownish. Tint visible to the naked eye, even when mounted.
2. Clarity - The second quality a diamond is judged by is clarity grade. Clarity is how many "inclusions” are in the diamond crystal. The fewer there are, the rarer the diamond will be…more light will reflect from the diamond, and the diamond becomes more valuable.
The Gemological Institute of America (GIA) grades diamond clarity using 10X magnification. They tag diamonds as:
Fl, Flawless - No internal or external flaws.
IF, Internally flawless - No internal flaws. Slight external blemishes.
VVS1 & VVS2, Very, very slightly included - Minute inclusions. Difficult for even an experienced grader to detect.
VS1 & VS2, Very slightly included - Minute inclusions. Not easily seen by an experienced grader.
SI1 & SI2, Slightly included - Inclusions that are noticeable to an experienced grader.
I1 & I2 & I3, Included - Obvious inclusions that may affect transparency and brilliance.
3. Carat Weight - The third quality characteristic is the diamond's weight. A carat is a measuring unit of the diamond weight and therefore the size.
Carat weight is used as a measure for other gemstones, but different gems of the same weight aren't necessarily the same size, because some gemstones are more dense than others--meaning that they pack more weight into a smaller space.One carat is divided into 100 points. A diamond of 25 points is described as quarter of carat or 0.25 carats and a diamond of 75 points weighs 0.75 carat.
It is interesting to know that in 250 tons of diamond bear, there is only a single one carat diamond in gem quality. That is why Diamonds are divided into weight groups and a one-point difference in a diamond weight can change the weight group of this diamond and make a huge difference in value.
Larger diamonds are more rare and in more demand than smaller diamonds of the same quality, so they can be sold for a higher price. A one carat diamond solitaire ring is nearly always more expensive than a diamond ring made up of multiple diamonds that are similar, but smaller, even though they total one carat or more.
Diamonds that weigh just under the next full carat are typically less expensive than diamonds passing the full-carat hurdle. In her interview for About Jewelry, Antoinette Matlins offered this opinion about carat weight:
Carat - weight is the easiest of the 4 C's to determine and it is your primary consideration when making this purchase. As the carat weight of a diamond increases so does its rarity and therefore it's price, but remember - Big is not necessarily better.
4. Cut - Of all the 4 C’s, Cut is directly influenced by the human element.
The cut of a diamond determines its brilliance. There is no single measurement of a diamond that defines its cut, but rather a collection of measurements and observations that determine the relationship between a diamond's light performance, dimensions and finish. Most gemologists consider cut the most important diamond characteristic because even if a diamond has perfect color and clarity, a diamond with a poor cut will have dulled brilliance.
Good proportions - When a diamond is cut into good or ideal proportions, the diamond is better able to handle light. The light that enters from the top of the stone is reflected from one facet to another in the stone and then dispersed back to the top ofthe diamond. This creates the sparkle and the scintillation to the eye of the observer.
Shallow cut - Light is lost out the bottom causing the diamond to lose brilliance.
Deep cut - Light escapes out the sides causing the diamond to appear dark and dull.
The first and easiest way to evaluate cut is to compare the Diamond’s weight with the next proper diameter size:
Ideal cut diamond model will have a diameter measure of 6.5mm in order to reflect Light to its optimum.
The shallow cut model will measure 6.5mm+ and will "leak" light.
Deep cut diamond will measure only 6.Omm and will have the physical size of a .85 Carat diamond.
Diamonds that are cut into good proportions will have more value. The maximum amount of light will be reflected and greater brilliance will appear. Cut is a matter of beauty, craftsmanship, mathematics and value.
~ Professional Definitions