A marvel of nature, formed deep within the Earth over millions of years. Each gemstone possesses unique qualities and characteristics, making it truly one of a kind.
Grown rather than found, but chemically identical to a natural stone. Same properties, same beauty, less cost.
Look past the sparkle. A stone can mark a birthday, an anniversary, a beginning - and people have been reading meaning into them for a very long time. Most customers arrive with a reason before they arrive with a colour.
When white light meets a coloured gemstone’s surface, some rays are reflected and some travel into the gem. The gem absorbs some colours and transmits others. The transmitted rays reflect within the gem, exit the stone, and return to your eye as body colour.
The highest quality gemstones are graded for the purity of their hue, the depth of tone, and their colour saturation.
As you will appreciate, there is much more to colour grading. Hopefully, this gives you a more in-depth overview of how grading works.
Its basic overall colour is a combination of hue, tone, and saturation determined by its selective absorption of light.
Smooth, polished facets reflect some of the light that strikes it. The light that’s not reflected enters the stone. The white light is split into its spectral colours, and the gem absorbs some of the colours and transmits the rest to the viewer. This is called selective absorption.
Hue is the first impression of a gemstone’s colour. It might be described as red, orange, yellow, green, blue, violet, or purple. The best gemstones exhibit a pure colour and no other colours except opals.
This GIA Hue wheel shows how the colours are described when other hues are present. E.g. B = Blue is pure Blue, and vslgB = very slightly green Blue. The capital letters are the strongest colour.
The degree of darkness or lightness of colour represents the depth of colour, ranging from colourless to black. Gemstone tone is described as “light,” “medium-light,” “medium,” “medium-dark,” and “dark.”.
The strength of the colour, or its intensity, refers to the degree to which the gem is free from brown or grey hues. The most desirable gemstones, which show little grey or brown, are often described as having “vivid” or “strong” colour saturation.
The gemstone grading system is similar in some ways as for diamonds. However, inclusions will not necessarily detract from the beauty or desirability of a coloured gemstone.
Gemstone clarity refers to external or internal characteristics/marks formed naturally when the crystal was created. Some gems have more inclusions than others, so finding a perfect gemstone in all types is not possible, so it’s a compromise when looking at its colour and marks.
This image shows an included and less included Emerald.
Unlike diamonds, there isn’t an “ideal” cut geometrically configured to maximise the brilliance of a gemstone. A high-quality gemstone cut presents the most even colour. It exposes the fewest inclusions, maximising the colour displayed when viewing the gem face up.
Like diamonds, fine-quality coloured gems usually have a table, crown, girdle, pavilion and culet. Some gems are cut as cabochons, which is a domed shape.
When looking at a gemstone, ensure that all the facets are symmetrical, as they will reflect light evenly across the surface, and the polish is smooth, without any chips or scratches.
If a gem is cut too shallow it can form a window, so if placed over a printed page face up, you can see the lettering through the gem. It can also cause darker areas called extinction.
Gemstones can be cut into various shapes and styles, each with a unique character.
A gemstone's weight is referred to as Carat. One Carat weighs one-fifth of a gram. There are 100 points to one Carat.
The carat weight of a gemstone does not necessarily allow you to accurately envision the size. Different gemstones have different densities (mass per unit volume), so two gems that appear to be the same size may have very different weights. For example, a sapphire is more dense than a diamond, so a one carat sapphire will look smaller.
Many coloured gemstones available today have been treated or enhanced to improve their colour, clarity, durability or overall appearance. Some techniques, such as heating and oiling, have been used for centuries, while others involve modern technology.
The frequency and type of treatment vary considerably between different gemstones. Fine untreated examples of certain gemstones, particularly ruby and sapphire, can be considerably rarer and may command a premium.
Treatments should always be disclosed where appropriate, particularly where they affect the value, appearance, durability or care requirements of a gemstone.
Heat treatment involves exposing a gemstone to controlled high temperatures to alter or improve its colour, clarity or appearance.
It is one of the most widely used gemstone treatments and is commonly associated with ruby, sapphire, tanzanite, aquamarine, zircon and several other gemstones.
For most commonly heat-treated gemstones, the resulting changes are considered stable and permanent under normal wearing conditions.
Impregnation involves introducing wax, polymer, plastic or a similar substance into a porous gemstone to improve its appearance, durability or stability.
It is commonly associated with porous materials such as turquoise, lapis lazuli and some forms of jade.
The treatment may be affected by excessive heat or chemicals and can therefore require special care.
Coating involves applying a thin layer of material to all or part of the surface of a gemstone to alter its colour, appearance or, in some cases, durability.
Coatings can include lacquer, ink, foil, resin or thin metallic or metal-oxide films. Coated gemstones can be more susceptible to scratching, abrasion, heat or chemicals and may require additional care.
Bleaching uses chemical or physical agents, or sometimes light, to lighten, remove or make a gemstone’s colour more uniform.
The treatment is commonly encountered in materials including jadeite, pearls and coral. Bleaching may sometimes be followed by impregnation to improve the appearance or durability of the material.
Dyeing involves introducing colouring agents into a porous or fractured gemstone to change, intensify or make its colour more uniform.
The stability of dyes varies. Some may fade when exposed to prolonged light or may be affected by chemicals and solvents.
Irradiation exposes a gemstone to a controlled source of radiation to alter its colour. It may subsequently be heated to produce or modify the final colour.
The treatment is commonly associated with blue topaz and is also used with diamonds, quartz and some other gemstones.
The stability of the resulting colour depends upon the gemstone and treatment. Some irradiated colours are extremely stable, while others can fade when exposed to strong light or excessive heat.
Fracture or cavity filling involves introducing substances such as oil, resin, wax or glass into surface-reaching fractures or cavities.
The treatment can make fractures less visible, improve apparent clarity or transparency and, in some cases, improve stability.
Emeralds, for example, are commonly clarity-enhanced by introducing colourless oil or resin into surface-reaching fissures. Some rubies may contain glass-filled fractures.
Because the stability of filling materials varies, filled gemstones may require special care and should generally be protected from excessive heat, chemicals and some cleaning processes.
Lattice diffusion involves heating a gemstone in the presence of particular chemical elements, allowing those elements to enter its crystal lattice and change or enhance its colour.
The treatment is most commonly associated with sapphire and ruby. Depending upon the elements used and the treatment conditions, the colour alteration may penetrate only a short distance beneath the surface or considerably deeper into the gemstone.
The colour produced by diffusion treatment is generally stable, although stones with shallow colour penetration can be affected by repolishing or recutting.
Unlike diamond grading certificates which are now commonplace, gemstone certificates are generally not available. Therefore it’s a case of trust and the sellers’ knowledge that will determine the quality of any stone.
Fewer laboratories grade gemstones GIA, Gueblin, Gem & Pearl Laboratory [London], Birmingham Assay Office. Certificates should display the information below.
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