How to choose? Here we present a brief guide to the qualities of gemstones, and how to buy them, starting with diamonds.
The value of a diamond depends on an assessment of the four Cs—that is, carat, cut, clarity and colour. Carat indicates the weight of the stone; a carat corresponds to 200 milligrams (about 1/140th of an ounce).
Cut refers to the cutting of the diamond. The cut should be of excellent quality with facets at specific angles so that it perfectly reflects the light and creates a ‘fire’ inside. A diamond with at least 56 facets, a table and a point may be called a brilliant. That does not mean other cuts are less precious, for there are many ways to cut a stone and to bring the best out of it. Whether round, tear-shaped, oval or cone-shaped, the most important requirement is that the cut should be appropriate to the stone.
Clarity refers to the purity of the stone. The number, size, and location of any inclusions, transparency, and possible structural irregularities are assessed. In addition, a distinction is made between defects visible to the naked eye and those that can be seen by a 10-power magnifying loupe. The highest grading is FL for ‘flawless’. Then comes IF, ‘internally flawless’, meaning that no inclusions are visible with the same magnifier. The grades below include VVS, ‘very very slightly imperfect’, and VS, ‘very slightly imperfect’ with inclusions invisible to the eye, visible only with some difficulty with the magnifier; these do not affect the stone’s brilliance. SI, ‘slightly imperfect’ and I, ‘imperfect’, have inclusions that can be seen with the naked eye, and may affect the stone’s brilliance.
Diamonds are graded for colour, with the ideal being colourless. This is an important, sought-after characteristic because it allows the white light to penetrate the stone unhindered, emerging as a rainbow. Most stones are situated between ‘D’, which is ‘colourless’, and ‘Z’, which is light yellow. The colour is determined by comparing the stone with an internationally fixed number of master stones. So-called ‘fancy’ diamonds which may be blue, red, green or even black, are another story.
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Ruby, king of the precious gems:
For thousands of years, the ruby has been considered king of the gemstones. It has everything a precious stone should have: magnificent colour, excellent hardness and outstanding brilliance. In addition to that, it is an extremely rare gemstone, especially in its finer qualities.
Ruby is the red variety of the mineral corundum, one of the hardest minerals on Earth, of which the sapphire is also a variety. Pure corundum is colourless. Traces of elements such as chrome, iron, titanium or vanadium are responsible for the colour. These gemstones have excellent hardness. On the Mohs scale their score of 9 is second only to diamond. Only red corundum is entitled to be called ruby, all other colours are classified as sapphires. The close relationship between ruby and sapphire has been known only since the beginning of the 19th century. Until then, red garnets or spinels were also thought to be rubies (which is why the ‘Black Ruby’ and the ‘Timur Ruby’, two of the British Crown Jewels, were so named, when they are not rubies, but spinels.)
Ruby consists of aluminium oxide and chrome as well as traces of other elements. In really fine colours, and good clarity, it occurs only rarely. Paradoxically, it is actually the colouring element chrome which is responsible for this scarcity.
Millions of years ago, when the gems were being created deep inside the Earth’s core, chrome gave the ruby its wonderful colour. But at the same time it was also responsible for causing a multitude of fissures and cracks inside the crystals. Thus only few ruby crystals were given the conditions in which they could grow undisturbed to considerable sizes and crystallise to form perfect gemstones. For this reason, rubies of more than 3 carats in size are very rare. So it is no wonder that rubies with hardly any inclusions are so valuable that in good colours and larger sizes they achieve top prices, surpassing even diamonds in the same category.
Some rubies display a wonderful silky shine, the so-called ‘silk’ of the ruby. This phenomenon is caused by very fine needles of rutile. Now and then, one of the rare star rubies is found.
The most important thing about the ruby is its colour. Two magical elements are associated with the symbolism of this colour: fire and blood, implying warmth and life. So ruby-red is not just any colour, it is absolutely undiluted, hot, passionate, powerful colour.
Which is the most beautiful ruby? The red of a ruby may involve very different nuances depending on origin. The range of those nuances is wide, and could perhaps be compared to hotel categories, from luxury accommodation down to a plain inn or hostel.
If the gemstone experts refer to a ‘Burmese ruby’, they are talking about the top luxury category. However, it does not necessarily follow that the stone is of Burmese origin. It is basically an indication of the fact that the colour of the ruby in question is that typically shown by stones from famous deposits in Burma (now Myanmar): a rich, full red with a slightly bluish hue. The colour is referred to as ‘pigeon-blood-red’.
A connoisseur will immediately associate this colour with the legendary ‘Mogok Stone Tract’ and the gemstone centre of Mogok in North Myanmar. Here, the country’s famous ruby deposits lie in a mountain valley surrounded by high peaks. Painstakingly, gemstones of an irresistible luminosity are brought to light in the ‘valley of the rubies’. Unfortunately, really fine qualities are quite rare even here. The colour of a Burmese ruby is regarded as exceptionally vivid. It is said to display its unique brilliance in any light, be it natural or artificial.
Ruby deposits also exist in Vietnam, near the Chinese border. Rubies of Vietnamese origin generally display a slightly purplish hue. Rubies from Thailand, however, often have a darker red which tends towards brown. This ‘Siamese colour’— an elegantly muted deep red—is considered second in beauty only to Burmese colour. Ceylon rubies, which have now become very rare, are mainly light red, like ripe raspberries.
Other ruby deposits are in India, Northern Pakistan in the Hunza Valley, Kashmir, Tadzhikistan, Laos, Nepal and Afghanistan. Kenya and Tanzania surprised the experts by their beautiful, strong colour rubies, which vary from light to dark red. But in the African mines too, fine and clear rubies of good colour, purity and size are very rare. Usually the qualities mined are average.
Colour is a ruby’s most important feature; transparency is of secondary importance. So inclusions do not impair the quality of a ruby unless they decrease the transparency of the stone or are located in the centre of its table. On the contrary: inclusions within a ruby are said to be its ‘fingerprint’, a statement of its individuality and, at the same time, proof of its genuine and natural origin. The cut is essential: only a perfect cut will underline the beauty of this valuable precious stone in a way befitting the ‘king of gemstones’. However, a really perfect ruby is as rare as perfect love.
To arrange an appointment in Hatton Garden to view or discuss gemstones and designs, please call us on 020 7399 2960.
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