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Diamond Cut

by Eli Butbul

The cut of a diamond is one of the most important diamond characteristic as it provides the diamond with its unique sparkle and brilliance as the cut allows the maximum amount of light to enter and leave the diamond. Of the Four Cs, the cut is the only value factor that is a result of human skill. It refers to the angles and proportion of a diamond, as well as its polish and precision of faceting. Often the cut of a diamond is mistakenly referred to as the shape (round, pear, oval, etc.) of the stone.

Well-cut diamonds can reflect light like a mirror from one facet to another and disperse and reflect this light through the top of the stone. A well-cut diamond will be symmetrically round, proper depth and width and have uniformity of the facets. These features will result in optimal radiance. On a classic round brilliant-cut diamond, for example, 57 or 58 facets must be precisely aligned so light will enter the diamond and reflect back through the large top facet, or table of the diamond. Diamonds that are cut either too deep or too shallow can lose light through the sides and bottom and will be less brilliant, and ultimately of less value.

The universal cut grading scale, as defined by the American Gemologist Society Laboratories (AGSL), is outlined below. Currently, only round diamonds are graded. GoldeNet Australia does not carry any diamonds below the cut grade of ‘Good’.

IDEAL CUT: Represents roughly the top 3% of diamond quality based on cut. Perfectly proportioned with the highest grade of polish and symmetry. This grade of diamond reflects virtually all light that enters it. They are the most brilliant, rare and expensive diamonds.

EXCELLENT CUT: Represents roughly the top 8% of diamond quality based on cut. Proportioned to fit strict requirements for table and depth percentage. This grade of diamond reflects almost all light but less than the ideal cut. They are still quite rare and very expensive.

VERY GOOD CUT: Represents roughly the top 15% of diamond quality based on cut. Proportioned to reflect much of the light that enters. This is a high quality and moderately priced diamond.

GOOD CUT:Represents roughly the top 25% of diamond quality based on cut. Proportioned to reflect most light that enters. These are considerable value, quality diamonds.

FAIR CUT:Represents roughly the top 35% of diamond quality based on cut. Disproportioned but allows some light to be reflected. GoldeNet Australia does not carry this grade of diamond.

POOR CUT:This includes all diamonds that do not meet the proportion standards of a fair cut. Disproportioned so that most light entering is lost out of its sides and bottom. GoldeNet Australia does not carry this grade of diamond.

Important characteristics of a diamond cut are described below. Some diamond cutters will compromise on the cut of the diamond in an attempt to optimise the diamond’s weight (carat). This can result is a larger diamond with a duller appearance. If all Cs are equal (cut, carat, colour and clarity), there can be as much as a 50% variation in the cost of a diamond if the cut is of poor quality.

TABLE SIZE %: The table length relative to the diameter of the diamond. A table that is too large or too small will reduce the overall dispersion of a diamonds brilliance.

CROWN ANGLE: Angle between bezel facets and girdle. Crown % is a measurement that relates to the depth of the crown to the diamonds overall depth.

GIRDLE THICKNESS: Ranges from extremely thin to extremely thick (assessed visually). Extremely thin or extremely thick girdles are less desirable than more moderate girdles.

DEPTH %: Measurement of the distance from the table to the culet (bottom-most point). A depth that is too shallow or too deep will allow light to escape through the bottom of the stone, reducing the stones overall fire and brilliance.

CULET SIZE: Ranges from pointed to extremely large (assessed visually). Unless the culet is abnormally large, it generally has no impact on the value of a diamond.

SYMMETRY: Refers to the overall uniformity of the cut of a diamond and is graded poor to excellent. Symmetry is based on the diamonds proportions, the relation of one facet to another. A diamond with good symmetry can be more attractive than a less symmetrical stone. Stones with poor symmetry can actually appear off-centred.

POLISH:The overall quality and uniformity of the polish of a diamond. It is graded poor to excellent based on the final finish applied to the facets and facet junctures by the cutter. Well-polished diamonds permit maximum passage of light and prevent potentially streaky surfaces.

Which Cut Grade should I choose?

For a diamond with the best cut, that will look exceptional even when viewed under a microscope, you need a diamond that reflects the most brilliance. These diamonds are cut to the most exacting proportions and have the highest polish and symmetry grades for round diamonds and have either excellent or very good for princess-cut, emerald-cut, and Asscher-cut diamonds.