Diamonds FAQ

What are gemmological characteristics of diamonds?

Carat

The carat weight of a diamond measures its mass. One carat is defined as exactly 200 milligrams (about 0.007 ounce). The point unit equal to one one-hundredth of a carat (.01 carat, or 2 mg) is commonly used to denominate the size of diamonds of less than one carat. All else being equal, the value of a diamond increases exponentially in relation to carat size. Larger diamonds are both rarer and more desirable for use as gemstones.

Total carat weight (t.c.w.) is a phrase used to describe the total mass of diamonds or other gemstone in a piece of jewellery, when more than one gemstone is used. Diamond earrings, for example, are usually quoted in t.c.w. when placed for sale, indicating the mass of both diamonds together and not each individual diamond.

Clarity

Diamonds are graded by the major societies on a scale ranging from Flawless, Very Very Slightly included (VVS), Very Slightly included (VS), Slightly Included (SI) to Imperfect.

Clarity is a measure of internal defects of a diamond called inclusions. Inclusions may be crystals of a foreign material or another diamond crystal, or structural imperfections such as tiny cracks that can appear whitish or cloudy.

Diamonds become increasingly rare when considering higher clarity grading. Only about 20 percent of all diamonds mined have a clarity rating high enough for the diamond to be considered appropriate for use as a gemstone.

Most inclusions present in gem-quality diamonds do not affect the diamonds' performance or structural integrity. However, large clouds can affect a diamond's ability to transmit and scatter light.

Colour

A chemically-pure and structurally-perfect diamond is perfectly transparent with no colour. The colour of a diamond may be affected by chemical impurities and/or structural defects in the crystal lattice. Most white diamonds are discounted in price as more yellow hue is detectable, while intense pink or blue diamonds (such as the Hope Diamond) can be dramatically more valuable.

Most diamonds used as gemstones are transparent with little tint, or white diamonds.

Diamonds with unusual or intense coloration are sometimes labelled "fancy" by the diamond industry. Intense yellow coloration is considered one of the fancy colours, and is separate from the colour grades of white diamonds. Gemmologists have developed rating systems for fancy coloured diamonds, but they are not in common use due to the relative rarity of coloured diamonds.

Cut

The cut of a diamond describes the manner in which a diamond has been shaped and polished from its beginning form as a rough stone to its final gem proportions. The cut of a diamond describes both the shape a diamond is formed into, as well as the quality of workmanship. Diamond cutting is the art and science of creating a gem-quality diamond out of mined rough.

Shape

Diamonds do not show all of their beauty as rough stones; instead, they must be cut and polished to release the characteristic fire and brilliance that diamond gemstones are known for.

Diamonds are cut into a variety of shapes that are generally designed to accentuate these features.

The modern round brilliant has 57 facets (polished faces), counting 33 on the crown (the top half above the middle or girdle of the stone), and 24 on the pavilion (the lower half below the girdle).

Diamonds which are not cut to the specifications of a round brilliant shape (or subsequent variations) are known as fancy cuts. Popular fancy cuts include the baguette (from the French, resembling a loaf of bread), marquise, princess (square outline), heart, briolette (a form of the rose cut), and pear cuts.

Generally speaking, these "fancy cuts" are not held to the same strict standards as round brilliants. Cuts are influenced heavily by fashion: the baguette cut which accentuates a diamond's lustre and downplays its fire was all the rage during the Art Deco period, whereas the princess cut which accentuates a diamond's fire rather than its lustre is currently gaining popularity. The princess cut is also popular amongst diamond cutters: of all the cuts, it wastes the least of the original crystal. The past decades have seen the development of new diamond cuts, often based on a modification of an existing cut. Some of these include extra facets. These newly developed cuts are viewed by many as more of an attempt at brand differentiation by diamond sellers, than actual improvements to the state of the art.

Quality

The quality of a diamond's cut is widely considered the most important of the four Cs in determining the beauty of a diamond; indeed, it is commonly acknowledged that a well-cut diamond can appear to be of greater carat weight, and have clarity and colour appear to be of better grade than they actually are. The skill with which a diamond is cut determines its ability to reflect and refract light.

The cutting process

The process of shaping a rough diamond into a polished gemstone is both an art and a science. The choice of cut is often decided by the original shape of the rough stone, location of the inclusions and flaws to be eliminated, the preservation of the weight, popularity of certain shapes amongst consumers and many other considerations. The round brilliant cut is preferred when the crystal is an octahedron, as often two stones may be cut from one such crystal. Oddly shaped crystals such as the macle are more likely to be cut in a fancy cut that is, a cut other than the round brilliant which suits the particular crystal shape.

Even with modern techniques, the cutting and polishing of a diamond crystal always results in a dramatic loss of weight; rarely is it less than 50%. Sometimes the cutters compromise and accept lesser proportions and symmetry in order to avoid inclusions or to preserve the carat rating. Since the per-carat price of diamond shifts around key milestones (such as 1.00 carat), many one-carat diamonds are the result of compromising "Cut" for "Carat". Some jewellery experts advise consumers to buy a 0.99 carat diamond for its better price or buy a 1.10 carat diamond for its better cut, avoiding a 1.00 carat diamond which is more likely to be a poorly cut stone.