Introduction to Diamonds
The 4 C's
As with modern cut diamonds we still valuate diamonds using the 4 Cs, Carat weight, Color, Clarity and Cut.
Diamonds are weighed in carats, the first C. One carat is equivalent to 1/5th of a gram. The carat measurement is metric so we further divide a carat into hundredths. Each hundredth is called a point. More small diamonds are found than large diamonds resulting in the higher price per carat for successively larger diamonds due to this inherent rarity.
The second C is clarity and refers to the purity of the diamond. Diamonds are formed deep in the earth and are subject to tremendous heat and pressure which cause internal inclusions and external blemishes. Most diamonds have inclusions and key identifying characteristics and very few are flawless. We identify and grade diamonds based on these characteristics specific to their size, nature and location in/on the stone. Diamonds are graded by a skilled observer with 10X magnification using a binocular microscope or 10X loupe with optimum lighting conditions.
The grading categories range from flawless to imperfect.
||Very Very Slightly Included
||Very Slightly Included
Flawless diamonds must be free from internal inclusions and external flaws. Internal graining not visible face up and without discoloration or small naturals on the girdle as long as they to not flatten the girdle are acceptable in the flawless grade.
Very, Very Slightly Included Diamonds are just that. These diamonds usually require a microscope to grade as the inclusions are very, very small and difficult for a skilled observer to see.
The Very Slightly Included grade is used for diamonds that have very small internal and external characteristics that are difficult to locate with 10X magnification and a skilled observer.
Slightly Included diamonds have small to medium sized inclusions that are obvious when examined with 10K magnification but usually not visible to the naked eye.
I1, I2, I3
Imperfect diamonds have medium to large flaws that are usually obvious to the unaided eye. Durability may be an issue with the lower qualities.
|D E F
||G H I J
||K L M
||N O P Q R
||S T U V W
||X Y Z
Diamonds occur in all colors of the rainbow however most diamonds range from colorless to light yellow or light brown. We use the GIA grading scale for color. The top color is D which is colorless. D, E and F are colorless to the human eye, G, H, I and J are near colorless, K, L, and M are faint yellow and the alphabet continues to Z and then diamonds have enough color to be called fancy. In order to determine the specific color range of a diamond we use a controlled lighting environment and master color grading diamonds for comparison. The chart above shows how little difference there is from one color grade to the next. Because colorless diamonds are purer with less chemical impurities to absorb light they are able to reflected and refracted more white light resulting in a brighter diamond. The more body color the diamond has the more light is absorbed.
The word cut refers to the proportions and finish of a polished diamond.
The European cut and the modern round brilliant cut are more alike than different. Both cuts have 58 facets in the same configuration. The modern round brilliant is technically more precision cut than its European cut predecessor. I like to take a few steps back when discussing diamond cuts. Most diamonds start as an octahedron rough, an eight sided natural crystal resembling two 4 sided pyramids joined at the base.
Until the late 19th century diamonds were very rare and cut for maximum weight retention from the rough shape. The old mine cut diamonds were chunky with a square outline with a small table and large culet (top & bottom facets) reflecting the crystal shape that they were cut from.
Old European Cut
Ideal Round Brilliant
By the early 20th century cutters realized that the fire and brilliance of a diamond is greatly increased when the proportions and angles between facets were of certain dimensions making more beautiful diamonds. The modern cutting style was facilitated by modern technology and some of the weight retention problems were rectified with the advent of the diamond saw. The European cut was the earliest versions of the new modern cut. The top, table, facet was still fashioned smaller, the crown (top) of the diamond a bit heavier with steeper sides, the pavilion main facets shorter and the culet larger than the current modern round brilliant which can be cut to precision for perceived maximum reflection and refraction of light. I say perceived because different environments and viewing angles (to name two modifiers) can easily be different. The European cut, due to its smaller table and greater crown area, breaks the light up and acts like a prism so the diamond can scintillate with the fire of spectral colors when rotated. The larger table size on the modern diamonds allows for more light to be returned to the eye of the viewer directly without interference. This direct light is known as brilliance.
The proportions are the angles, their measurements and their relationship to one another. The specific parts of the cut diamond measured are the table percentage of the diameter, the crown angle, the pavilion angle, The total depth percentage of the diameter, The crown height percentage of diameter, the pavilion depth percentage of diameter, lower girdle facet percentage of pavilion depth, the star facet percentage of the crown and the girdle thickness.
The finish is thequality of polish and the symmetry of the diamond and all the facets. The optical attributes of a diamond are Brightness, Fire and Scintillation.
Brightness, also called brilliance is the effect of the internal and external reflection of white light. The proportions of the diamond play the main role in determining the brightness.
Fire refers to the flashes of color resulting from the white light being dispersed into spectral colors.
Scintillation refers to the areas of light and dark when viewing the top of the diamond.
All these are factored with design and craftsmanship to assign a cut grade of Excellent, Very Good, Good, Fair or Poor using the GIA Cut-grading System for round brilliant cut diamonds.