How to choose the perfect Gem
At Holts, we have compiled a guide which is specifically designed to provide you with all the important knowledge you might require when purchasing a coloured gem. Learning a few things will assist you in making an educated purchase of a gemstone not only you love but is the highest quality within your price range.
Like Diamonds, you can still use the 4 C’s of Cut, Carat weight, Colour and Clarity as a general guideline to understand a gems quality. However when purchasing a coloured gemstone listen to your instincts, colour is an extremely personal matter and is viewed differently person to person. Some might have a preference for the highly prized cornflower blue of the Sapphires found in Kashmir, whilst others might be drawn to the inky dark blues of the Sapphires found in Australia. The choice is up to you….
Cut
The 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 viewers eye is important.
Well placed facets and aligned angles, proportion and symmetry are made by the cutter to create the best cut stone from the rough he is provided with. If a stone is well cut then there should be no obvious areas of darkness, called extinction. This is where the stone is too deep so light enters the stone, however does not return to the viewer’s eye. The stone should also not have any areas of distinct lightness, where light shines straight through. This is called a window, as literally you can see right through the stone.
There are many types of cut shown in coloured gemstones, such as round, oval, cushion,mixed,heart, marquise, trillion, emerald, cabochon, free form, princess and pear.
Colour
A gemstone’s colour is determined by 3 variable factors. These are hue, saturation and tone.
The hue of a gemstone is another word for its colour, so this might be red or blue or green. This can also be a combination of two colours or hues, for example greenish blue and yellowish orange. For the majority of most gemstones a pure hue is most desirable, so green or red.
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 less ‘punchy’ than those which are highly saturated. Lowly saturated gemstones can also take on a greyish tinge. This is not as desirable as a stone which has high saturation and commands a higher price.
The final factor is tone. The term tone relates to the relative lightness or darkness of the gem. For example pink has a light tone and maroon has a dark tone. Typically the most desirable gemstones have a medium or medium to dark tone.
Carat weight
The weight of coloured stones and pearls are expressed in carats, with one carat equaling exactly 200mg or a fifth of a gram. This 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 it was standardized that one seed of the carob tree matched 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 in one gemstone won’t look the same size as one carat in another gemstone, as some gems have a higher Specific Gravity and are thus denser than others. For instance a carat of amber 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.
Clarity
All gemstones which are natural in origin have some variety of inclusions within, formed during or after the gems formation thousands of miles deep near the centre of the earth. There isn’t just one type of inclusion, there are many from included crystals, rutile needles, fissures and vial like inclusions containing liquid. Some inclusions are characteristic to a particular type of stone, for example discoid fractures in peridot called ‘water lilies’, ‘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 gemstone types typically form with inclusions and thus are to be expected, such as emerald.
Holts Lapidary has a wide range of loose gemstones and luxury gemstone jewellery in our showroom in Hatton Garden, contact us today on 0207 405 5286 or visit us to have a consultation with one of our qualified Gemologists or a specialist Bespoke Designer.