Coloured Stones
A guide to coloured gemstones
For centuries, coloured gemstones have captivated and fascinated people from all walks of life. Poets and artists have used gemstones to symbolize love, passion and supremacy. Coloured gemstones are available in virtually the entire colour spectrum and many have characteristics that classify them as “phenomenal” gems.
JCS offer a huge selection of gemstones in every shape and colour available. JCS supply coloured gemstones which are ethically sourced and we can offer advice regarding care requirements and disclose treatments as necessary for all gemstones we present.
Most gemstones are inorganic minerals that have a specific chemical composition and often contain trace elements that cause the colour in the gem. Other gems are organic – such as pearls, amber, coral and even hair has been used in jewellery – but to be classified as a gem, a material must have the following qualities: –
- Beauty
- Rarity
- Durability
Colour in gemstones
The most important value factor for all gemstone varieties is colour. Some gemstone come in many different hues (basic colours – red, green, blue etc) – e.g. tourmaline comes in many different colours and even sapphire is available in yellow, pink and other colours. Coloured gemstones are then also evaluated on the tone and saturation of the colour. Tone refers to the level of lightness or darkness of the colour. Saturation refers to the strength or intensity of the colour. Saturation is measured ranging from weak to vivid.
The importance of cut
Gems are wonders of nature and, unless a coloured gemstone has been treated in some fashion (see below), then cut is the only human contribution to the beauty of a gemstone. A good cut can accentuate the beauty of a gemstone. Cut factors include symmetry and surface lustre, or brilliance.
Treatments
Some gem varieties are commonly treated for use in jewellery. These treatments include colour change or colour enhancement or sometimes measures such as filling a gem with an epoxy or oil to prevent fracturing or drying out.
Gemstones, when found in nature do not always have the intensity, or evenness of colour deemed desirable for use in jewellery. Human intervention is often needed to render these gemstones to their full potential. Heat-treating and irradiation are often used to enhance, change or improve a natural gemstone’s colour. For example, did you know that virtually all Tanzanite on the market has been heat treated to change its colour? When tanzanite is found in nature it is brown in colour – the heat treatments cause colour change to the lovely velvety blue. The colour change is permanent.
JCS will advise of any known treatments and recommend care requirements accordingly. Many treatments commonly used today are permanent.
Phenomenal Gems
Some gemstones – because of their extraordinary characteristics – are classified as “phenomenal” gemstones. Examples are: –
- Opal
- Cats eye Chrysoberyl
- Moonstone
- Star sapphires and star rubies
You are probably aware of opal and its play-of-colour – flashes of many different colours seen when the gemstone, the observer or the light source moves. Opals with greater play-of-colour are more highly prized than those with a lesser degree of play-of-colour.
Star rubies and star sapphires (both from the same mineral species corundum) are gemstones cut in the cabochon form (a smoothly rounded – as opposed to faceted – polished gemstone usually with a domed top) and which then displays a six-ray “star”. A gemmologist would refer to these phenomena as asterism.
JCS are always happy to advise on and demonstrate all the above attributes for individual gemstones we stock or can source. If you have any queries regarding any of the above then please call 01277 637 187.