Diamond Cutting & Grading

After diamond is recovered, it is separated into two categories, gem-grade and industrial-grade. Gem-grade diamonds are of the highest quality and are the stones that, historically, people have taken extreme measures to acquire. These precious stones only account for only one quarter of all diamonds mined each year. All others are used for industrial purposes.

The environment a diamond is produced in determines whether the stone has the makings of an industrial diamond or a gem. The conditions that affect the growth of diamond, such as steady versus fluctuating temperature and/or pressure, appear to control whether a given diamond is a gem or industrial grade stone. Where growth has been restricted or where relatively high concentrations of impurities, like graphite or other minerals, are present, the result will likely be industrial-grade diamonds.

A diamond's unparalleled hardness makes it the most important cutting tool to industry, science and modern medicine. The cutting agent found in surgical scalpels, engraving tools, metal-cutting tools, grinding wheels and drill bits is often diamond. Diamond also coats dentists' drills, making dental work faster and more tolerable.

Industrial diamonds are often ground into powder and used as an abrasive agent to cut and polish gem-grade stones, including diamond itself. More unique uses of diamond include infrared windows in heat detectors and special windows on spacecraft.

Gem-grade diamonds are sent on a journey to various locations across the globe to be cut, graded, mounted and sold. The world's primary cutting centers are located in New York, Antwerp, Tel Aviv and Bombay.

The process of dividing a diamond into sections is referred to as cleaving. The way in which a rough diamond is cleaved is an important element in determining the value of each crystal. A chisel-like blade is used to cleave the diamond into two or more stones.

Diamond has a grain, similar to wood, which is used as a guide when splitting the stone. If not cleaved correctly, a diamond will shatter, which is why it can take months of agonizing planning before the first cut is made.

Diamond cutting is quite labor-intensive. Each individual section, must be cut and polished with great precision and care. Cutting a single diamond requires hours of planning and grinding as well as a high degree of skill. The diamond is placed on a grinding plate that is coated with olive oil and abrasive diamond powder to shape the crystal.

When a diamond is cut, the dull, opaque pebble is transformed into a magnificent mirror of light. The way in which a diamond breaks light is determined by the stone's cut. The placement of each facet (tiny mirror) is mathematically determined to produce the maximum fire, sparkle and beauty. The final phase of the finishing process is to polish each individual facet with progressively finer grades of diamond dust.

The most sought after shape is the round brilliant-cut stone with a total of 58 facets, standardized crown and pavilion angles and ideal table proportions. Each facet is ground and polished by hand and strategically aligned with the others to make the maximum use of light. The amazing detail involved in the production of a single cut diamond can result in a gem that bends, breaks and bounces light rays within the stone, transforms them into rainbow array of colors, then ejects the colorful fragments outward into the world.

When a rough diamond is cut and polished, approximately half of its total weight is lost in the process. In fact, less than one percent of diamonds will produce stones of one carat or more once finished. Certain shapes spare more of the stone than others. For example, an octahedral diamond crystal will produce the largest cut gem when cut with the brilliant round shape, thus loosing the least weight as waste.

The most universally accepted standards used to grade diamonds are the four C's: carat, color, clarity and cut. The first C, carat, refers to the unit of weight for diamonds and other precious gems. One carat equals 0.2 grams, and there are 142 carats in an ounce. Carats are divided into 100 points, offering the most precise weight possible. The second C, color, typically comes from a naturally occurring impurity within the diamond. Some diamonds, however, are colored artificially by irradiation or special coatings. With a few exceptions, the less color a diamond displays, the more valuable it is.

The color of a diamond is measured with the Gemological Institute of America color scale, in which D is the highest/purest rating, and Z describes a diamond with a heavy brown cast. Due to the minute differences between color gradations, it is virtually impossible for an untrained eye to distinguish them on the color scale. A yellow tint can first be seen by the (untrained) naked eye around the I or J scale grades. The term fancy color refers to diamonds with distinctly attractive natural color, such as the dark blue Hope Diamond, the Black Orloff and the golden brown Earth Star.

Clarity refers to the lack of imperfections such as scratches, cracks, blemishes and flaws or inclusions. Most diamonds have imperfections. Some are more obvious than others, but many are so small they cannot be seen without a magnifying glass or microscope. The Gemological Institute of America rates clarity on a scale that begins with the grade of "flawless." The gradations progress from "very very slightly included" to "slightly included" to "imperfect."

Gia Clarity Scale

(Fl) Flawless - shows no inclusions or blemishes of any sort under 10X magnification when observed by an experienced grader

(IF) Internally Flawless - has no inclusions when examined by an experienced grader using 10X magnification, but will have some blemishes

(VVS1 and VVS2) Very Very Slightly Included - contains minute inclusions that are difficult even for experienced graders to see under 10X magnification

(VS1 and VS2) Very Slightly Included - contains minute inclusions such as crystals, clouds or feathers when observed with effort under 10X magnification

(SI1 and SI2) Slightly Included - contains inclusions (clouds, included crystals, knots, cavities and feathers) that are noticeable to an experienced grader under 10X magnification

(I1 I2 and I3) Included - contains inclusions (possibly large feathers or large included crystals) that are obvious under 10X magnification and may affect transparency and brilliance

The final C, cut, refers to the shape, facet design and finish of the stone. The relationship between size, shape, symmetry and cutting angles of a stone all play a role in evaluating the cut of any gem.

While over 75 percent of all diamonds sold are round stones, diamond solitaires are available in the following seven basic shapes: round brilliant-cut, marquise, emerald-cut, princess-cut, pear-shaped, oval and heart-shaped.

Image
Shape
	round brilliant-cut
	marquise
	emerald-cut
	princess-cut
	pear-shaped
	oval
	heart-shaped

photos courtesy of Gemological Institute of America