Inorganic Gemstones

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Coating

  • Nature of gemstone: Coating is done on almost any gem stone. Coating can be performed both on rough and cut stones.
  • Materials used: Wax, plastic, paints, resins, reflecting coloured papers and metallic foils, sputtering techniques etc. are used.
  • Possible effects:
    1. In diamond, a special coating is performed known as Carbon Vapor Deposition (CVD) where a thin layer of synthetic diamond is deposited over a colourless stone to imitate diamond. One the latest coated colours are the black and green coated diamonds. The black diamonds appear opaque black but may actually be dark browns which are semi transparent in transmitted light. The coating is probably due to a layer of diamond - like carbon (DLC).
    2. In the case of colourless topaz or quartz a thin layer of gold is deposited over the colourless topaz or quartz to produce a blue colour. This has been marketed under the trade name aqua aura. A variety of metallic elements are currently being used to produce different colours which are subsequently marketed as red aura etc.
    3. A coloured paper or metallic foil is pasted on the pavilion facets of cut gemstones or the base of the cabochon to enhance the colour as well as the quality of light reflected from the stone.
  • Identification:
    1. Detection in loose stones can be done by boiling with acids or using a hot point or by scratching the stone with a pointed fragment.
    2. In the case of mounted stones, with the help of a lens, examine the back portion of the stone through the table. Some form of crinkling or wrinkling of the coating or foiling is visible.
    3. Identification is also possible by a careful examination of the unevenness of colour on the surface.

Did you know?

Jewellery is one of the most bought products online. An estimated $1 billion USD of diamonds are bought annually via the Internet. Over 40 million people use the Internet to trade!

In Germany, the garland of ambers is hung around the necks of the infants, so that their teeth might come out without much trouble.

In Turkey, people fix a piece of amber in the hubble-bubble, dogged by an age old belief that the presence of the jewel would destroy all the germs and no disease would spread, even after many have dragged their puffs from it.

In Greece, people think if wine is poured into the cups made of amethyst, one does not get drunk after drinking that.

In Rome, a talisman having coral pieces is considered very auspicious to quell the bad spells of evil look. The Romans were in the habit of hanging chains made of ancient coral pieces from the cradle of the infants to protect them from evil effects.

In China, people wear rings studded with tiny conch or oyster shells as they believe it cures all aches such as stomach ache, worms and like.

In India, pendants made of silver and studded with pearls are hung from the necks of the children to save them from any bad effects.

Greeks still believe, if women wear blue sapphires then no sense of immorality would pollute their mind nor can any fear of the supernatural can trouble them.

The Pope Innocent III had circulated an order asking all the priests wear blue sapphire, so that morality can be strengthened.

It is said about turquoise, that when the stone changes its color into yellow, it actually signals bad times to the person who wears it.

It is believed that a turquoise gifted to a friend or a lover turns his or her life into one of happiness and good luck.

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