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The value of any diamond is determined by the “4 Cs”: cut, colour, clarity and carat. Understanding the diamond’s certificate and the factors that affect its cost will help the buyer make a confident and informed purchase.
Diamond is said to be the hardest of all the naturally occurring minerals. That makes the process of cutting diamonds both difficult and expensive. Nevertheless, humans have been drawn to working that mineral since the first rough outlines of cutting were produced around 1400 AD.
The art of diamond-cutting continued to be honed and improved all the way up to 1939, when it was perfected in Germany with the Praktischer Feinschliff, known in English as the Practical Fine Cut. That perfectly rounded shape has 32 upper facets, 24 lower facets, as well as the table (top) facet, making 57 facets in all.
The “brilliant” mineral diamond is one of the most sought-after and beloved stones in the world. Its optical qualities are exceptional. Indeed, each ray of light entering through the table or the crown bounces around several times inside the stone before re-emerging and reaching the eye of the observer. Just like in the arrangement of the facets, we can also observe a perfect regularity in the dimensions of the stone. Each cut is a work of art and this is one of the most important value criteria, since it is for its brilliance and vivacity that the diamond is so prized.
There is a variety of diamond cuts for applications in costume jewellery. They are rarer because the shape of the rough diamond does not lend itself easily to such applications. The gem cutter, or lapidary, chooses the shape of the stone by observing in great detail the inclusions and the material to get the best out of it each time. The most common diamond cuts are: pear, princess, trillion, marquise, oval, cushion, emerald, baguette, trapeze, square, and briolette (drop-shaped). The proportions of these cuts are all just as important as for the brilliant cut and are detailed in the same way on the certificates.
Any lack of proportion results in a loss of “brilliance”. Cutting defects are indicated on the certificate and result in a lower price. Features to look out for:
- The “symmetry” or “finish grade” indicates that the proportions of the diamond are very good, good, average, or poor.
- The term “polish” indicates the quality of the diamond polish: very good, good, average, or poor. A very good polishing gives the diamond a highly particular aspect referred to as “adamantine lustre”. That particular characteristic has never been successfully reproduced in any imitation diamond.
- The term “girdle”. The girdle is the outer line around the stone. It is observed by examining the side view of the diamond. It can be extremely thin or very thick, but thin is best. When it is somewhat thick, it can be simply chipped (bearded or fringed), or polished and faceted. The latter is preferable, as it produces a more finished and lustrous stone.
- The observations sometimes mention one or more extra facets. Additional facets may be cut to camouflage a natural defect or a cutting defect.
The examination of the colour is a decisive factor when determining the value of a diamond. The colours are grey, pink, blue, brown, and the most common one, yellow. Note that the whiter the diamond, the more valuable it is.
When the shade of these tones is very faint, the diamond is classified as white. Colour scales have been established in various countries, but the Gemological Institute of America (GIA) colour scale is the international authority.
To examine the colour of a diamond, the stone must be placed in a fold of very white bristol paper and observed from the overhead view to avoid disturbance from the reflections of the facets. This is how the stone can be seen at its most transparent, which allows the observer to more closely examine the material.
Purity determines the number of visible inclusions in a diamond, as most crystals contain inclusions:
- “Feathers” are cracks or fractures that generally follow the cleavage plane. A crack can be closed (encased inside the stone) or open (when it reaches the surface of the stone)
- Gaseous or liquid inclusions, which are often undetectable with a jeweller’s “loupe”, or magnifying glass.
- Solid inclusions: the presence of other more or less microscopic crystals. These can be of a variety of natures (graphite, diopside, diamond, garnet, zircon, quartz). These imprisoned materials sometimes make it possible to determine the origin of a stone, since certain materials are found only in specific regions of the world.
International standards are used to gauge the degree of purity of diamonds. The purity grades of a diamond are determined by the size and position of the inclusions. The criteria are always assessed by an examination of the diamond as viewed from the table and the crown.
The degrees of purity, in descending order, are:
IF (Internally flawless): no internal defects visible with a 10x magnifying glass.
VVS1 and VVS2 (Very Small Inclusions): minuscule inclusions barely perceptible with a 10x magnifying glass.
VS1 and VS2 (Very Small Inclusions): very small inclusions detectable with a magnifying glass by a moderately trained eye.
SI1 and SI2 (Small Inclusions): small inclusions visible with a magnifying glass.
P1 (1st Pique): inclusions very easily visible with a magnifying glass, but difficult to see with the naked eye.
P2 (2nd Pique): large or numerous inclusions slightly affecting the brilliance of the stone.
P3 (3rd Pique): large and numerous inclusions distinctly affecting the brilliance.
The weight of a diamond is measured in carats. One carat is equivalent to 0.2 grams. The weight of small diamonds is expressed in points, each point is one-hundredth of a carat (0.01 Ct).
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