Diamond Grading

The 4Cs: Colour, Clarity, Cut, Carat Weight

Diamonds are graded based on the following four criteria. You can either link to each separately, or scroll down through the entire page.

Colour

Clarity

Cut

Carat Weight

Sorting it all out

CARAT WEIGHT

Diamond was first discovered in India around 500 B.C. The first unit of weight used for diamond was the carob seed; the weight of a seed from the seed pod of the carob or locust tree was equivalent to a 1.00 ct. (carat) diamond.

Today diamonds are weighed using the metric carat system:

1 metric carat = 0.2 grams
1 metric carat = 200 milligrams
1 metric carat = 1/142 ounce
A carat is divided into 100 points, so…

1/4 ct. = 25 points = .25 ct.
1/3 ct. = 33 points = .33 ct.
1/2 ct. = 50 points = .50 ct.
3/4 ct. = 75 points = .75 ct.

Do not confuse carat with karat. Carat refers to stone weight, while karat refers to fineness of gold.

As a diamond's weight increases, the price per carat increases to reflect the fact that larger diamonds are more rare and may also have higher colour, clarity and cut grades. Basically, the rarer, the more expensive.

A note about weight retention...

A diamond may have extra, unnecessary weight. Weight that does not enhance the fineness, appearance, of largeness. This may happen when the girdle is too thick. For example:

Consider two different stones with exactly the same grades and dimensions, with the exception of girdle thickness. When these diamonds are mounted they look pretty-much identical. However, the one with the thick girdle weighs more so it will be more expensive, even though they may look identical.
 

COLOUR

According to the GIA (Gemological Institute of America) colour grading scale. Diamonds are separated into basic colour groups:

1. colourless
2. near colourless
3. light yellow, grey or brown
4. fancy-(red, green, blue, orange, purple, pink, yellow, black and exotic colours like cognac, chartreuse, and others)

The regular GIA scale for grading colour in diamonds begins with D and ends with Z. Here is the scale: (due to the differences in computers and browsers these colours are not exact):

D (icy white), E F (colourless), G H I (near colourless), J K L M N to Z (light to darker hints of yellow, brown, and grey). After Z they are graded as fancy colours.

The less colour a diamond possesses the more valuable it becomes due to its rarity. If a diamond is coloured, it will command value only when it reaches the point of saturation where it becomes rare or if the colour itself is rare. These are called fancy colours - In 1987 Sotheby's auctioned an approximately .95 ct. pink to purplish natural fancy colour diamond and received over $800,000 due to its rarity.

Most diamonds are near colourless to light yellowish. There are only about 25 impurities that effect diamond colour. In fact, 99.95% of all diamond is pure carbon. Some impurities that may cause colour in diamonds are:

- nitrogen...yellow
- boron...blue
- crystal irregularities...pinks, browns and reds
- natural radiation...green
 

About 50% of all diamonds are fluorescent, some even glow. This fluorescence is caused by the reaction between the light's energy and the diamond's atoms. Diamonds that fluoresce usually do so in blue.

To grade colour, gemologists use master stones (stones graded and recorded at the GIA gem trade lab), white light and a variety of other proper procedures.
 

CLARITY

 Diamonds which have inclusions (flaws) visible to the naked eye are what would usually be called commercial quality and are rated the lowest on the clarity scale (I1, I2, or I3) . Many of the cluster diamond rings sold at "discount" stores will have this effect (under normal light). Many treated stones also begin at this grade.

On the GIA clarity scale VS2 means very slight inclusions. The subscript 2 has to do with location of the inclusions, not the number of inclusions. The scale starts with flawless (no visible inclusions or blemishes when viewed using 10x magnification by a trained eye) and ends with I3 ( highly visible inclusions easy for the unaided eye to see). The following is the GIA clarity scale:

In this scale we measure the degree of internal inclusions and external blemishes. Inclusions can be small and/or large, they can appear white and/or black; the more inclusions and the easier they are to detect determines the clarity grade. Blemishes, on the other hand, are external and are such things as scratches, nicks, abrasions and chips that may appear on the surface of the diamond.

On a certificate or well done appraisal these internal and external characteristics are recorded on a diagram called a plot. All inclusions are plotted in red, blemishes in green, and extra facets and prongs in black. Following are lists of some internal and external characteristics and terminology used.

EXTERNAL CHARACTERISTICS
natural - unpolished surface, the original skin of the diamond rough
pit - small indentation on a facet surface
cavity - opening on surface
nick - minor surface chip
grain/twinning line - irregularity in atomic grain, the crystal growth
scratch - small grove (can be from normal wear)
abraided facet junction (can be from normal wear)
out of round - diamond circumference not symmetrically round

INTERNAL CHARACTERISTICS
cleavage or feather - occurs along atomic grain
fracture - irregular shaped break
included crystal
carbon spot - included crystal (dark)
pinpoint - small included crystal(appears white)
cloud (group of pinpoints)
internal grain line
laser drill hole
bearded or feathered girdle - minute to small hairline fractures extended from the girdle into the stone

The clarity not only dramatically affects the price, but can be a good indication of the diamond's vulnerability. Heavily included diamonds can be dangerous to wear because the type and number of inclusions could make it prone to breaking.

CUT

Whether you prefer a round, pear, emerald cut, marquise or heart shape, the shape of the diamond and make (proportion and finish) are both elements of the CUT. The better the diamond has been cut (i.e. the better the make) the more beautiful the diamond will appear.

The make is the overall appearance. If the diamond is pleasing to the eye, it probably has very good angles, good facet junctions, and a nice finish (polish). To better understand make, look at the three following diagrams:

Light travels best in the third diagram - it has the best dimensions, angles and finish, so light exits through the top of the diamond as sparkle. Because of a poorer cut, the other diamonds loose that sparkle through their undersides.

In 1919, a European diamond cutter and mathematician presented his Doctoral Thesis depicting the "Ideal Proportions" of a round diamond. The ideal cut allows more lively, brighter and visible spectral colours to appear from the crown facets.
 

In addition to the angles and proportions, the finish, which includes the overall polish of the diamond, the condition of the girdle (thickness and texture) and culet (not being nicked, chipped, abraided, out of alignment or off center), and the symmetry of the facets (meeting at the apexes and correctly positioned) are essential to the beauty and appearance of the well cut and proportioned diamond.

Diamonds are cut from their rough, natural state. The diamond rough is studied thoroughly by an expert so as to decide how the diamond rough should be cut to yield the best value. After marking the diamond with India ink sawing and/or cleaving, girdling, faceting and polishing is performed.

Note that the cut of a diamond is not the shape of the diamond. The most common shapes seen are round, oval, marquise, pear, emerald cut and heart shape. The most brilliant of these is the round brilliant. The following are some average cutting times for specific diamond shapes:

Round brilliant............2-4 hours
Oval brilliant...............8-10 hours
Marquise shape..........12 hours
Emerald cut................14-16 hours
 

SORTING IT ALL OUT

 Now that you know a little bit about cut, colour, clarity and carat weight it's time to sort it out....

The choice at hand:

In addition, the cut of the .74ct. is better than the .79ct. Of course, the clarity is not (The VVS₂ is a better clarity grade than VS₂.). The colour grade of the .74ct. is G which is not as good as the .79ct. F stone. Also, the prices are essentially the same.

What to do:

Consider that the .79ct. diamond appears dark in the centre when viewed under normal light, from the table facet (from the top). This is an indication of a deep pavilion. Now, had the same diamond appeared whitish around the table, called a fisheye, then this would indicate a shallow diamond. In reality, the .05ct. weight difference between the two stones is miniscule, the dark centre detracts from the appearance, and the colour grade G is next to F (i.e. not a big difference). Therefore, it seems the .74ct diamond is the better choice. Price would be very similar for these two diamonds. Keep in mind that the .74ct. is cut better, making it more beautiful, it is probably the diamond to go with.