How to choose the perfect GemAt Holts we have compiled a guide which is specifically designed to inform you of everything you need to know before purchasing a coloured gem. Taking a little time to consider a few pointers will assist you in making an educated decision, ensuring your purchase is not only a stone you love but also one of the highest quality within your price range.
As for Diamonds, the 4 Cs of Cut, Carat weight, Colour and Clarity can be used as a general guideline to understanding a coloured gem’s quality. However, when purchasing a
coloured gemstone, listen to your instincts – colour is an extremely personal matter and perceived differently from person to person. Some may have a preference for the highly-prized cornflower blue of the Sapphires found in Kashmir, while others might be drawn to the inky dark blues of those found in Australia. The decision is all yours!
Colour A gemstone’s colour is determined by three variable factors: hue, saturation and tone.
The hue of a gemstone is another word for its colour, for example red, blue or green. It may also be a combination of two colours, such as greenish blue or yellowish orange. Since a pure hue is most desirable for the majority of gemstones, many purchasers frequently opt for what they perceive to be the ‘reddest’ red or ‘greenest’ green, for example.
The saturation of a gemstone is the intensity or strength of the colour present within the stone. Gemstones with low saturation appear washed out and may have a greyish tinge, their overall impact being less ‘punchy’ than those which are highly saturated. The latter consequently tend to be more desirable and command a higher price.
The final factor is tone. The term tone relates to the relative lightness or darkness of the gem. Pink, for example, has a light tone while maroon has a dark one. Typically, the most desirable gemstones have a medium or medium to dark tone.
CutThe cut of a gemstone has a very important role in determining its overall attractiveness. A pleasing shape and even distribution of light being returned to the viewer’s eye is important.
The cutter determines well-placed facets and aligned angles, proportion and symmetry to create the best cut stone from the rough he is provided with. If a stone is well-cut, there should be no obvious areas of darkness, known as extinction. These are areas where the stone is too deep and light enters the stone but does not return to the viewer’s eye.
Conversely, the stone should not have any areas of distinct lightness, where light shines straight through. These are known as windows, as you can literally see right through the stone.
Coloured gemstones can be fashioned in a vast array of cuts, from the familiar round, oval, cushion, cabochon, heart and marquise to the more unusual trillion, free form and carved.
Carat weight The weight of coloured stones and pearls are expressed in carats, with one carat equalling exactly 200mg or a fifth of a gram. The term carat came from a French word derived from the Greek ‘keration’, literally translating as ‘fruit of the carob tree’ or ‘ceratonia siliqua’. Carob trees were fairly abundant in the Middle East and it was found that the seeds they produced were fairly uniform in weight, subsequently resulting in the standardisation that one seed of the carob tree equalled one carat. One carat consists of 100 points, so 25 points equals a quarter of a carat, 50 points equals half a carat and so on.
However, one carat of one gemstone will not be the same size as one carat of another, as some gems have a higher Specific Gravity than others and are therefore denser. A carat of Amber, for example, will be significantly larger than a carat of Hematite. Amber is a lot lighter than Hematite and subsequently there will be more of it to make up to the weight of one carat.
ClarityAll gemstones which are natural in origin have some variety of inclusions within, formed during or after their formation, thousands of miles deep near the centre of the earth. Many types of inclusion exist, from crystals, rutile needles and fissures to vial-like cavities containing liquid. Some inclusions are characteristic to a particular type of stone, for example discoid fractures in Peridot referred to as ‘ lily pads’, ‘rain’ in Aquamarine, ‘rutile needles’ or ‘silk’ in Sapphires and ‘centipedes’ in Moonstone. These inclusions act as diagnostic features which aid in identifying the gemstone, proving it to be natural.
Ideally, a gemstone should have no visible inclusions, especially stones which are light in tone. However, some gemstones, such as Emerald, typically form with inclusions and these are thus to be expected.
At Holts we have a wide range of
loose coloured gemstones and
gemstone jewellery in our showroom in Hatton Garden. Contact us today on 020 7405 5286 or visit our showroom to have a consultation with one of our qualified Gemmologists or a specialist Bespoke Designer.