Diamonds are graded by independent grading labs whose expert gemmologists evaluate each of diamond's particular characteristics, such as carat weight, colour, clarity, cut and fluorescence. To standardise pricing and to simplify selection we have grouped diamonds into four quality categories - Budget Grade (K-M, I1-2), Premium Grade (I-J, SI1-2), Deluxe Grade (G-H, VS1-2) and investment Grade (D-F, VVS1-2). Each grade has a specific set of characteristics that falls into its own pricing range.
Diamonds are weighed in carats. Carat is a measure of weight, not the size. One carat is equal to 0.2 grams, it is divided into 100 points. For example, a 30-point diamond weighs 0.30 carats. Because a fraction of a carat can make a difference in cost, diamond’s weight is often measured to the hundred thousandths of a carat, and then rounded to a hundredth of a carat on the certificate.
Diamond colour is all about what you can’t see. Diamonds are valued by how closely they approach colourlessness or whiteness. Most commercial diamonds offered by jewellery shops are white with slight hints of yellow or brown. The colour scale begins with the letter D and continues with increasing presence of colour to the letter Z. Diamonds are colour-graded on specialized equipment under controlled lighting and precise viewing conditions.
Diamond clarity refers to the absence of marks and inclusions. Diamonds without blemishes are rare, which increases a diamond’s value. Diamonds are assigned a clarity grade that ranges from internally flawless (IF) to diamonds with obvious inclusions (I3). This scale contains 11 grades, with most diamonds falling into the VS (very slightly included) or SI (slightly included) categories. In determining a clarity, the system considers the size, type, position, and quantity of inclusions visible under 10× magnification.
Diamond’s cut quality is the factor that determines its brilliance. The fire and beauty of a particular diamond depends more on the cut than anything else. Each measurement and proportion component is assessed individually, taking into account the relative importance of that component in the overall cut quality of the diamond. Each grade represents a range of proportion sets and face-up appearances. Cut grades range from Excellent to Poor, with Very Good and Good being the most common. Typically a round brilliant cut diamond has 57 facets. The large, flat facet on the top is the table. The proportions of a diamond refer to the relationships between table size, crown angle and pavilion depth.