The most important characteristics of diamonds are carat weight, colour, clarity and cut (the 4 C's).
Carat is the most misunderstood of the 4Cs. It actually refers to a diamond's weight, not the diamond’s size. 1 ct = 0.2 gr
The highest quality diamonds are colourless, while those of lower quality have noticeable colour, which manifests as pale yellow in diamonds. The Gemmological Institutes grades diamond colour on a scale of D (colourless) to Z (light yellow or brown).
D - Highest, absolutely "colourless" grade
E - A "colourless" grade. Traces of colour difficult for even trained eye to detect.
F - A "colourless" grade. Faint colour detectable by a trained gemologist.
G - The highest "near-colourless" grade. Colour may be detectable when compared to much higher "colourless" grades. Excellent value.
H - A "near-colourless" grade, colour is only noticeable when compared to much higher colour grades.
I - Colour may be only slightly detectable upon close examination
J - The last of the "near-colourless" grades, colour may be slightly detectable to the unaided eye
K-Z - The first of the "faint" colour grades, meaning colour may be detectable to the naked eye
Diamond clarity is the assessment of small imperfections on the surface and internally. The surface flaws are called blemishes, and internal defects are known as inclusions. These tiny, natural blemishes and inclusions are microscopic and do not affect a diamond’s beauty in any way. Diamonds with the least and smallest inclusions receive the highest clarity grades.
FL-IF - No internal or external characteristics
VVS1-VVS2 - Very, very slightly included. Characteristics miniscule and difficult to see under 10x magnification, even to a trained eye
VS1- VS2 - Very slightly included. Minor inclusions ranging from difficult (VS1) to somewhat easy (VS2) to see at 10x magnification.
SI1- SI2 - Slightly included. Inclusions noticeable at 10x. Best value if eye-clean. SI2 inclusions may be detectable to a keen unaided eye.
I1-I2-I3 - Included. Diamonds may have minor eye-visible inclusions.
The round brilliant cut diamond is by far the most popular and most researched diamond shape available today. Other cuts are marquise, oval, emerald, princess, asscher, radiant, pearl, heart.
Excellent - Diamonds in this range are considered the finest and exhibit a rare and stunning interaction between light and the stone's facets. They reflect the light better than any other category of diamonds.
Very good - Diamonds in this range are considered as having the highest cut grade. The interaction of facets shows a good balance and delivers fire and brightness in a diamond.
Good - Diamonds in this range produce slight fire and sparkle compared to the ideal cut diamonds and deliver slight darkness.
Fair - Diamonds in this range reflect limited light and brilliance.