Buying a Diamond

When you purchase a diamond there are simple factors that combine to determine the quality and value of the individual stones you choose.

The important things to consider are “The Four C’s.” These comprise :

When you know what these terms mean you will feel more comfortable about making your choice, and we will be there to offer help and advice.

Certificated diamonds are a commodity whose characteristics are precisely defined to agreed international standards, and if you are looking at certificated stones the above qualities will be itemised.

Certificates are issued by testing laboratories and the internationally recognised establishments that you are likely to encounter are the G I A (the Gemmological Institute of America) and the H R D. (Hoge Raad voor Diamant, or The Diamond High Council of Antwerp.) In England the AnchorCert Gemmological Office is an increasingly accepted certificating laboratory, attached to the Birmingham Assay Office.

Going back to the Four C’s : although clarity, colour and cut are equally important the first thing you will probably discuss about your diamond will be its weight. This will be expressed in carats or fractions of a carat.

So what is a carat ?

From ancient times the word has been used as a term of weight for gold and precious stones and it is thought to originate from the practice of balancing the object to be weighed against a number of seeds from the Carob tree, the weight of which is remarkably consistent.

Today a carat is accepted as 200mg or 1/5 of a gram. A carat is divided into 100 points; thus a 1/4 carat = 0.25 points. You will frequently see carat abbreviated as ct and point as pt.

Colour

The colour tone of a diamond is denoted by a letter of the alphabet starting at D, regarded as colourless, to Z, denoting a strong yellow. Although the absence of colour is regarded as a good thing a very strong colour will make a diamond highly desirable. A blue, green or canary yellow diamond for instance would be sought after.

In practice you will have no trouble distinguishing between a D (colourless) and say a P (very faint yellow), but to tell the difference between H and I, both near colourless, takes a great deal of expertise.

Clarity

When your diamond was formed carbon was subjected to incredibly high temperatures and pressures deep inside the earth. Ideally the process would result in a crystal clear diamond, but more often than not the result was a crystal with small marks inside it. When the rough crystal is polished these marks become apparent; they show up as black dots and are known as inclusions. Again there is an international grading system to establish the degree of clarity awarded to a stone : the greater the degree of clarity, the more desirable the stone.

There are eleven grades of clarity, from FL (flawless no inclusions) to I/3 (inclusions visible to the naked eye.)

Cut

The cut of a stone describes its shape and there are eight basic shapes.

Whatever the shape of your diamond you will find the surface covered with small flats, which are called facets. The proportions of the basic shape and the way the facets have been cut on its surface are extremely important to the amount of “life and fire” that the stone exhibits.

Why are these so important ? We will use the round / brilliant cut diamond as an example.

On the top of the diamond (the crown) there are 33 facets and on the underside (the pavilion) there are 25 facets If the proportions of the stone are correct then you have the ideal “make”.

As light passes through the crown of the diamond its path is bent and it is reflected from one facet to another inside the diamond, then reflected back through the crown to the viewer, giving it its “sparkle”. At the same time the optical properties of the stone break up the light into the colours of the spectrum, creating the “fire”. To make the most of the diamond's natural properties the angles have to be exactly right; too steep or too shallow and light will escape through the pavilion. The same principles apply to all the cuts, but some are more successful at exploiting the diamond's natural properties than others.

There is one other property worthy of mention that you will see on a diamond certificate, which is fluorescence . This is caused by trace elements of boron found in the diamond and is activated by ultra violet light. You will find it on the certificate rated as :

None, Faint, Medium, Medium blue, Strong blue, or Intense blue.

Other colours do occur but the most commonly seen is blue.