What Are Some Basic Gemstone Treatments?

This brief gemstone treatment guide will help you to quickly assess a gemstone jewelry gift—and not make yourself crazy in the process. To become a truly expert buyer will require a major investment of your time, but you need to learn only a few basics to choose an anniversary or romantic gift.

Buy natural gemstone jewelry from a reputable jeweler, one who has professional associations with the American Gem Society (AGS) or the Jewelers Vigilance Committee (JVC) as fake gemstones can be passed off as natural stones quite easily on an unsuspecting buyer. If a stone looks "too perfect" there's a good chance that it's fake, or may have been treated with a non-standard method that leaves it unstable. Ask lots of questions, what you don't know can hurt your wallet.

Treatments or enhancements such as oiling and heating, are widely used for gemstones, so don't press your panic button—these are not deceptive practices. Without such treatments, your gemstone jewelry would look quite dull. There are few gems that are naturally perfect enough to use in jewelry. Records dating back to the 11th century exist about heat treatments being applied to rubies and sapphires.

Routinely Used Gemstone Treatments

  • Heating (thermal enhancement)  Used to change the color of some gems, such as aquamarine, and improve a gemstone's clarity. Applied routinely to rubies, sapphires, tanzanite, tourmaline, topaz, zircon and amethyst. This treatment lasts for the life of the gem. Disreputable dealers do not disclose this treatment and try to sell gemstones for more than they're worth.
  • Oiling  A natural, colorless oil, wax or resin is applied that fills minor imperfections and enhances a gem's clarity. Widely applied to emeralds, turquoise and alexandrite. Oiling will need to be repeated. The use of epoxy resins can harm a gemstone.
  • Bleaching  Lightens gems such as pearls and jade to even their color. This is an acceptable treatment.
  • Irradiation  A gamma, electron or neutron bombardment and heat treatment process used to change a gem's color, such as a blue topaz, which would remain a brown stone without irradiation. Some irradiation of gemstones occurs naturally in the mine.
  • Dyeing  Adds coloring matter to intensify or improve color. Pearls and black onyx are routinely dyed to even the color. Dyeing is not an acceptable treatment for jade, black opal and lapis lazuli.
  • Diffusion  Chemicals are used to produce color changes. Heat treatments may also be done along with diffusion on the same stone. Green topaz is created by diffusion. It is a permanent treatment.
  • Diffusion is also done on sapphires to produce the star effect (asterism) or other color changes, but this is a quite controversial treatment. The star effect occurs naturally from inclusions and diffusion is a forced effect. You should be informed that your stone is not a natural star sapphire, which is a lot more valuable.

Gemstone Checklist

When your head is spinning at the dizzying array of colors, cuts and shapes of gemstones, use this list as a guide:

  • Is the jewelry made with natural or synthetic gemstones?
  • Is the color vivid and even throughout the gemstones?
  • Does the stone have many inclusions? Light gemstones have more inclusions than darker ones.
  • A well-cut gemstone has even brilliance throughout. You won't see blotchy dark areas.
  • If you're buying earrings or cufflinks, the gemstones should match well.
  • Were any treatments done? If so, which ones and are they permanent? Get this in writing.
  • Are there any special care instructions?
  • How brittle, how susceptible to cracking or chipping is this type of gem? If you love a certain type of stone but it can easily chip, buy a pair of earrings or a pendant rather than a ring, bracelet or cufflinks.
  • In general, synthetic gemstones are more likely to be sold as natural gems in malls and even well-known chain department stores. Be very cautious, keep your receipts. If a price sounds too good to be true for a natural gemstone, it probably is a fake and not worth it at any price.

Here is a comprehensive gemstone guide for precious and semiprecious stones from the American Gem Trade Association.

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