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.
Given the rarity and unique visual properties, nearly all coloured gemstones sold are enhanced using various techniques. Many of these techniques have been used for centuries. High quality coloured gemstones that are not enhanced are rare and command high prices. There are many methods of enhancing coloured gemstones. The most common enhancements are below.
The application of heat to enhance the colour and/or clarity of gemstones has been a common practice around the globe for centuries. It is part of the standard polishing and finishing process for many coloured gemstones. As such, it is accepted by the jewellery industry and the American Gem Trade Association. The enhanced colour and/or clarity of heat-treated gemstones is permanent.
The filling of a gem material with an oil, wax, glass, resin or other material, coloured or colourless, to improve appearance. This process began centuries ago by gemstone merchants who found that immersing emeralds in oil or waxes made them look clearer to the unaided eye. This practice continues today with many coloured gemstones.
The use of wax, resin or oil applied to the exterior of a porous coloured gemstone to protect the natural substance and to improve sturdiness and appearance.
The application of chemicals or other elements to lighten or enhance colour consistency.
The act of adding colouring agents so that they permeate a coloured gemstone to enhance or alter the colour.
The alteration of a gemstone’s colour through the use of radiation. This is often followed by a heating process. The enhanced colour of irradiated gemstones is permanent.
Filling surface-reaching fractures or cavities with glass, resin, wax or oil to conceal their visibility and improve the apparent clarity of gem materials, appearance, stability, or in extreme cases—to add a slight amount of weight to a gem. The filling materials vary from solids (a glass) to liquids (oils). In most cases, they are colourless (coloured filler materials could be classified as dyes).
Heating a diamond to high temperatures under high confining pressures to remove or change its colour. Heating diamonds at high pressures and temperatures can remove or lessen their brownish colouration so the gem becomes colourless. Through this process, other types of diamonds may be transformed from brown to yellow, orangey yellow and yellowish green, or to blue colours.
This involves using a narrowly focused beam of laser light to burn an open channel from the surface of a diamond to reach dark inclusions. This is generally followed by the use of a chemical forced into the channel to dissolve or alter the appearance of the inclusion. Diamonds are the only gemstones to be treated in this fashion, partly because only they can withstand the heat of a laser.
The penetration of certain elements into the atomic lattice of a gemstone during heat treatment to change or accentuate its colour.
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 1-carat sapphire will look smaller.
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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