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Gemstone Treatment Guide

Published April 28, 2010 | Updated June 12, 2015

Most items that you come in contact with every day have been treated in some way: Clothes have been dyed, houses have been painted, and most wood has been pressure treated. Gemstones are not any different. When a gemstone is forming deep within the earth, natural heating and pressure occur. In order to bring more gemstones to the public, many companies continue that process with additional heating, pressure, or other treatment techniques. It is estimated that up to 80 percent of all gemstones have been treated in some way.

General Enhancement Categories:

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  • Treatment Code N

    Those natural stones which are not currently known to be enhanced by any methods, such as spinel, and therefore can safely be presumed to be untreated have the code N (not enhanced). The code may also be used for stones that are sometimes or often treated but in this particular case are unenhanced. To use this symbol on sapphire, for example, which is generally heated, means that the seller certifies that the particular stone was not heated and can supply a document such as an invoice or lab report so stating.

  • Treatment Code E

    Those natural stones which are routinely enhanced by traditional methods have the code E (enhancement). The particular stone given this designation may or may not be enhanced. For example, since most emeralds are oiled, an E would indicate such treatment but would not cover non-traditional methods, such as hardened plastic resins (like Opticon), which would require specific enhancement codes. Another example would be the use of E for aquamarine, which in most cases is heated prior to the sale of the rough to remove greenish tints. If the seller knows what specific treatment has been used, then a more specific code should be used.

  • Other Treatment Codes

    Those gemstones for which definite information on standard treatments is known or to which N and E codes do not apply due to non-traditional treatments, must disclose the specific treatment with the appropriate code. For example, a morganite that is known to have been heated would receive an H code rather than the less specific E code.

Specific Enhancement Codes:

  • Enhancement Code B

    Bleaching is the use of chemicals to lighten or remove a gem's color.

  • Enhancement Code C

    Coating is the use of surface treatments, such as films or lacquers, to provide color or other special effects. NOTE: This type of treatment is not permanent and can chip or wear off. Do not use harsh solvents or chemicals on jewelry with this type of treatment. Read our gemstone care guide for more information on protecting treated gemstone jewelry.

  • Enhancement Code CR

    This designation is used for any stone that is synthetic or laboratory created.

  • Enhancement Code D

    Dyeing is the introduction of coloring matter into a gem to give it a new color or greater intensity.

  • Enhancement Code F

    Filling is the incorporation of colorless borax or other substances into the cracks that are a by-product of heating the stone; it is used only if a crack is visible at 10x magnification.

  • Enhancement Code G

    This code refers to the use of gamma or electron irradiation for the purpose of changing a gem's color. Irradiation may be followed by a heating process to stabilize the color. Such stones do not exhibit residual radioactivity.

  • Enhancement Code H

    Heating a gem at a high temperature improves clarity, changes color, or creates phenomena in gems. Any filler materials that enter the gem as a result of the heat treatment must not be visible in fractures at 10x magnification.

  • Enhancement Code HTHP

    This is known as the High Temperature/High Pressure process. The combination of high temperature and high pressure is used to enhance or change the color of diamonds. The treatment is sometimes identified as HP.

  • Enhancement Code L

    Jewelers sometimes use a laser to drill into a stone and remove or alter an inclusion, specifically on diamonds. Lasering is the name of the treatment.

  • Enhancement Code O

    Oiling, or resin infusion, is the intentional filling of surface breaking cavities and cracks in transparent or translucent gems with a colorless oil, wax, resin, or man-made unhardened resin.

  • Enhancement Code R

    Irradiation is the use of neutron bombardment to alter color. This process creates residual radioactivity, and such stones must receive a Nuclear Regulatory Commission safety release prior to sale. The irradiation treatment often is used in combination with other radiation and heating treatments.

  • Enhancement Code S

    Bonding is the intentional use of a colorless agent (usually plastic) within a porous gemstone.

  • Enhancement Code TA

    Type A jade is natural jade enhanced only with wax.

  • Enhancement Code TB

    Type B jade is natural jade that is bleached in acid to remove undesirable staining, and then impregnated with wax or polymers.

  • Enhancement Code TC

    Type C jade is natural jade that is dyed and sometimes bleached and impregnated with wax or polymers.

  • Enhancement Code DS

    The diffusion treatment uses coloring and star-making chemicals to affect a gem's appearance. It adds specific chemicals to a high-temperature heating process to penetrate the surface layer (usually to a slight depth only). Such treatment is not generally accepted, and stones sold with this enhancement must be specifically labeled as diffused.

  • Enhancement Code W

    Waxing/oiling is the impregnation of colorless wax, oil, or paraffin into porous opaque gems to improve appearance.

  • Enhancement Code DBL - Doublet

    Jewelers make a doublet by gluing a thin layer of natural stone to a backing material. The backing material is used to thicken and give strength to the item.

  • Enhancement Code TPL - Triplet

    A triplet is a doublet that has a clear protective layer on top of the stone. The top layer may consist of clear quartz, glass, or hard plastic. This layer thickens and gives additional strength to the item.

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