Many gemstones have to be altered in order to enhance their appearance. This is usually done to produce colours not usually found in nature. Enhancement techniques improve colour, clarity, reduce porosity, stabilize colour and enhance durability. Depending on the stone and the treatment, such alteration may be easy or impossible to detect. Examples of some of the methods frequently used are: heat treatment, irradiation, impregnation, and assembled stones.
Many gems are heated under controlled conditions to improve colour as in, (aquamarine, sapphire, ruby, and tourmaline), alter colour (sapphire, amethyst to citrine, topaz, zircon), or improve clarity (sapphire, ruby). Since natural heating also occurs in volcanic areas, the artificial effects are indistinguishable. In most cases, the results of heat treatment are permanent.
Colourless topaz, yellowish diamonds are irradiated in large quantities and sometimes heated to produce various shades of blue, and a variety of colours. Other stones, such as tourmaline, are sometimes irradiated to produce new colours. In many cases, the effects of irradiation are somewhat unstable and can be reversed by heating.
Impregnation and Chemical Treatment
Turquoise being porous is sealed with wax, plastic resin to "stabilize" and improve the colour. Such material cannot be seen. "Black onyx", agate has been impregnated with sugar, and then carbonized by acid. Yellowish diamonds are sometimes coated on the girdle or pavilion with a thin bluish film to improve colour.
TJadeite is sometimes chemically "bleached" and impregnated to improve colour, and this treatment can be difficult to detect.
In recent years, a new treatment for corundum has appeared, in which poorly coloured corundum is heated in chemicals to deposit a very thin layer of enhanced colour on the surface of the stone. These stones can be quite impressive, but when re-cut the colouration comes off. Such treatment is easily detected by immersing the stone in a liquid with a high refractive index; where the colour appears to concentrate along facet edges. Diffusion-treated blue sapphires and Rubies are also known.
Thin seams of opal are often assembled with backing of opal or black onyx to produce a doublet, and a clear quartz top is added to produce a triplet. This makes the material useful while the dark backing enhances the play of colour and quartz top makes it durable. Opal doublets and triplets must still be protected against heat and liquids. If the adhesive layer begins to break down, the stone's appearance is marred, and it is difficult, to repair the damage.
Unless specifically marked as 'Natural' our gemstones may be treated to enhance their beauty. Such treatments and terminology comply with CIBJO guidelines and industry standards. Coloured pearls may be colour-enhanced. If you need any information on treatment permanence and any special care requirements, please email us at firstname.lastname@example.org. Download Our Treatment Guide.