SINGAPORE: Most people know about the 4 C’s for Diamonds but know less when it comes to choosing a high quality genuine coloured gemstone for a piece of jewellery.
When choosing a coloured gemstone, the choice of the stone usually begins with your favourite colours, but there’s more to knowing whether the stone is genuine than just liking the shade.
Whilst elements like cut and carat always come into play, colour becomes the stand-out feature with coloured gemstones, as does the treatment (or hopefully lack of treatment) the stone has gone through. Provenance of gemstones can also be interesting to look into, especially if you are considering investment pieces.
Colour saturation of gemstones: When considering the colour of a high-quality gemstone, the important thing to keep in mind is saturation. This is the colour’s strength or intensity, ranging from a dull hue to a pure, vivid hue.
Treatments of gemstones: For almost every gemstone that exists, there is also a treatment for it. The aim of these treatments is usually to enhance the colour of that particular stone. Some of these treatments are permanent, such as the heat treatment used on sapphires and rubies which removes undesired traces of yellows and browns to give clearer, more vivid colours.
Some gemstones such as Emeralds can be oiled to disguise their internal flaws, as the clear, or coloured, oil seeps into the internal fractures and makes them barely visible. This treatment is not stable, and over time oil will dry up. It is also potentially dangerous, as it makes concealed flaws would mean that the stone is more fragile than the buyer realises.
Gemstones can also be made stronger by filling up cracks and flaws with resin. Although this is a more ‘stable’ treatment than oil, these polymer resins do tend to go yellow with age, therefore changing the colour of your gemstone.
Which treatment is the best? No treatment at all. You can tell your gem is of the highest quality if it hasn’t been subjected to any treatments.
Provenance of gemstones: This is an important element when choosing a coloured gemstone if you want the stones to become investment pieces. As always, rarity is what makes a stone special.
For example, there is a specific colour of tourmaline containing copper which makes it neon blue. These “Paraiba Tourmaline” as they are called are named for the mine they were originally found in, located in the Paraiba province of Brazil. This mine has now “run dry” but other tourmalines containing copper and therefore displaying the same amazing colour have since been found in mines in Mozambique.
Still, Paraiba tourmalines from Paraiba itself are more of a rarity and therefore more valuable. Keep in mind though, that provenance is not as important as colour saturation and lack of treatments.
Want some tips on how to choose the right diamond? Read our ‘Diamonds Are Forever‘ story.
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