Before buying a coloured gemstone, you should know there are:
* Natural gemstones (from Mother Nature)
* Synthetic gemstones (made by man)
* Natural gems whose colour and clarity have been enhanced by man.
* Imitation gemstones (made from glass and plastics to look like natural gemstones) These are extremely cheap and easy to spot.
These gemstones differ widely in value and often are misrepresented by jewellers because they do not know the difference between a natural, synthetic and enhanced gems.
Important thus, to buy a gemstone accompanied by an identification and grading report from a qualified gemmologist.
What is a Synthetic Gem?
A synthetic gem has the same chemical composition, crystal structure, optical and physical proper ties as its natural counterpart. Synthetics have been around for many decades, and, as long as it can be identified as synthetic, its value will be substantially lower than that of a natural gem.
Today, nearly all types of coloured gems are made in the laboratory and sold as ‘cultured gems’ by most jewellery chains.
Synthetic diamonds are available and it is illegal to sell such a stone without describing it as either man-made, laboratory made or synthetic.
How are gemstones treated to look better?
The processes by which gemstones are treated to improve their colour and clarity are:
Using chemicals to lighten or remove colour is a very old process. Light coloured pearls and ivory are often bleached with hydrogen peroxide
Porous minerals readily absorb a dye which may improve their colour.
Lapis lazuli, jadeite, cultured pearls, agate and turquoise are often dyed.
- Cavity filling
Surface-reaching cavities are often filled with glass or plastic, especially with rubies and sapphires.
- Colour impregnation.
- Melted wax and other resins (sometimes coloured) are sucked under vacuum into pores and cracks to stabilise or colour a gem.
An Introduction to Gemstones
- Fracture filling
A process whereby thin fissures or cracks are filled with a colourless resin, glass,
plastic or oil (baby oil, cedar oil, etc), make fractures or cavities less visible and
improve the clarity of the gem. Emerald and ruby are the most commonly
- Heat treatment
This is one of the oldest and most common gem treatments. Heat can darken, lighten or completely change a gem’s colour. Heat can also eliminate, create or
alter the appearance of inclusions in a gem. The latter is very helpful in
Bombardment with x-rays or sub-atomic particles can change the colour of a gem. Such irradiation can create dislocations in the atomic structure that act as colour centers. The vivid blue of topaz is normally due to such a treatment.
- Lattice diffusion
When a gem is “cooked” under high temperature in a “soup” containing elements such as titanium, chromium, beryllium, etc, these elements diffuse into its crystal structure to give the gem a more marketable colour. Sapphire and ruby are treated in this way.
- Sugar and smoke
When opal is heated in concentrated fruit juice, sugar is absorbed by the
porous structure. After cooling and drying, the opal is treated with sulfuric acid which converts the sugar to carbon, thus darkening its colour.
A similar effect can be obtained by “smoking” a white opal.
- Surface coatings
The ancients were the first to discover that a gem’s colour can be improved by attaching a silver or gold foil “backing” to the gem.
Painting the surface of a gem is another method normally used with fraudulent intent.
Some gems, such as lo- grade turquoise or lapis lazuli, are crushed, the powder combined with dye and a bonding agent and the paste then moulded into the
shape of a polished gem. Look for dye concentrations under magnification.
- High Pressure/High Temperature (HP/HT)
HP/HT techniques are in use to remove or darken the colour of diamonds.
REST ASSURED: All gems from Prins & Prins are supplied with a Grading Report issued by a qualified gemmologist. Trust the experts