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Roy W. Macdonald FGA, DGA

Bespoke Jewellery Designer PO Box 100, Callander, FK17 8ZR Tel 07710 544321

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Gemstone Enhancements

 

The term enhancement is defined as any treatment or process other than cutting and polishing that improves the appearance (color/clarity/phenomena), durability, value or availability of a gemstone. In today’s gem marketplace, many gemstones have been enhanced by a variety of methods. Such processes may range from simple heating (such as with tanzanite) to high-tech irradiation (such as blue topaz).


I take enhancement disclosure seriously and guarantee, to the best of my abilities, to provide my clientel with complete information on any and all enhancements to which a gem has been subjected. While many enhancements are currently undetectable, I do my best to provide all the information you need for informed buying decisions.


The guidelines I follow are those of the American Gem Trade Association (AGTA) and are the most stringent in the industry. In addition,I have modified these guidelines slightly in areas where I feel they are not stringent enough (example: flux healing of ruby).


Some gemstone enhancements are less stable than others, meaning that the appearance of a gem may change with time.  A gemstone enhancement is considered stable as long as the gem does not change in appearance (color and/or clarity) under normal wear, cutting, cleaning, repair or display conditions. Gemstones can be divided into three basic enhancement categories.

 

  • Not Enhanced (N)
    The “N” symbol is used on our invoices to indicate one of two situations. First, there are certain gemstones that are not currently known to be enhanced (alexandrite, some garnets, etc.). Second, the “N” symbol may also be used for a gem where it can be proved via gemological or other means that a gem has not been subjected to any enhancement. When you see the “N” symbol on our invoice, we guarantee that the gem in question is unenhanced.
  • Normally Enhanced (E)
    The “E” symbol is used for gemstones that are routinely enhanced. Since many enhancements are difficult or impractical to prove definitively, unless otherwise indicated, our approach is to assume that such enhancements have been applied to that particular gemstone. This assumption is made to protect both buyer and seller. If a more specific method of enhancement is known, then the specific enhancement code will be used.
  • Nontraditional Enhancements (T)
    For gemstones not covered by the “N” and “E” symbols, a code covering the specific gemstone enhancement will be listed.

 

Symbols for Specific Forms of Enhancement

 

  • B = Bleaching: The use of heat, light and/or chemicals or other agents to lighten or remove a gemstone's color. This is often accompanied by subsequent dying and/or impregnation. Example: bleached cultured pearl; bleached/impregnated jadeite (‘B-jade’)
  • C = Coating: The use of such surface enhancements as lacquering, enameling, inking, foiling, or sputtering of films to improve appearance, provide color or add other special effects. Example: coated diamond
  • D = Dyeing (staining): The introduction of coloring matter into a gemstone to give it new color, intensify existing color or improve color uniformity. Example: dyed green jadeite
  • F = Filling: The filling of surface-breaking cavities or fissures with colorless glass, plastic, or some similar substance. This process will improve durability, appearance and/or add weight. Example: ruby
  • Fh = Flux healing: During heat enhancement, fluxes (or heat alone) may be used to heal fractures/fissures which were formerly open. The process dissolves the walls of the fractures and redeposits the molten gem material, healing the fractures closed. Example: ruby (particularly that from Möng Hsu, Burma)
  • H = Heating: The use of heat to alter color, clarity, and/or phenomena. Example: Ruby, sapphire, tanzanite, aquamarine, demantoid garnet
  • I = Impregnation: The impregnation of a porous gemstone with a colorless agent (usually plastic) to give it durability and improve appearance. Example: Stabilized turquoise
  • L = Lasering: The use of a laser and chemicals to reach and alter inclusions. Example: diamond
  • O = Oiling/Resin Infusion: The filling of surface-breaking fissures with a colorless oil, wax, resin or other colorless substances, except glass or plastic, to improve the gemstone’s appearance. Example: emerald
  • R = Irradiation: The use of neutrons, gamma, ultraviolet and/or electron bombardment to alter a gemstone’s color. The irradiation may be followed by a heating process.Example: blue topaz
  • U = Lattice (‘bulk’ or ‘surface’) Diffusion: Outside-in diffusion of coloring chemicals via high-temperature heat treatment to produce color and/or asterism. Example: lattice diffusion-treated sapphire
  • W = Waxing/Oiling: The impregnation of a colorless wax, paraffin and/or oil in porous gemstones to improve appearance. Example: jadeite

Natural Gemstone Enhancement Chart


(based on the AGTA Source Directory 2000–2001)

 

Natural
Gemstone
Enhancement
Symbol
Description
Used
Frequency
Encountered
StabilityCare
Requirements
AgateDUsuallyExcellent to goodNormal

Fire Agate

NNormal
AlexandriteNNormal
AmberE or HUsuallyVery good to good*Special
 DRarelyVariableSpecial
AmethystE or HOccasionallyExcellent*Special
AmetrineNNormal
AndalusiteNNormal
AquamarineE or HUsuallyExcellentNormal
BerylRMaxixeAlwaysPoorX-Special
 RYellowUsuallyVariableSpecial
 NYellow-greenNormal
 E or ORedCommonlyVery good to fairSpecial
ChalcedonyDBlackAlwaysExcellent to goodNormal
 DBandedUsuallyExcellentNormal
 DGreenUsuallyGood to fairSpecial
 DBlueCommonlyGood to fairSpecial
 E or HCarnelianUsuallyExcellent Normal
 DCarnelianOccasionallyExcellent to good*Special 
 DJasperOccasionallyExcellentNormal
 NChrysopraseNormal
ChrysoberylNTransparentNormal
 RCat’s eye OccasionallyExcellentNormal
CitrineE or HUsuallyExcellentNormal
CoralNBlack*Special 
 E or BWhiteCommonlyGoodSpecial
 E or WPinkCommonlyGoodSpecial
 IOrangeCommonlyGoodSpecial
 BGoldUsuallyVery good Special
 DRedOccasionallyVariableX-Special
Natural
Gemstone
Enhancement
Symbol
Description
Used
Frequency
Encountered
StabilityCare
Requirements
DiamondLOccasionallyVery good Normal
 CRarelyVery good to poorSpecial
 FOccasionallyVery good Special
 HPRarelyUnknownSpecial
Diamond – FancyROccasionallyExcellent to very goodSpecial
 LOccasionallyVery good Normal
 FRarelyVery good Special
 CRarelyFair to poorNormal
 HRarelyUnknownNormal
Diopside – Chrome N*Special 
EmeraldE or O UsuallyVery good to fairSpecial
 DOccasionallyVariableSpecial
GarnetNAll varieties *Special
 E or HSome demantoid CommonlyVery good *Special
HematiteNNormal
IoliteNNormal
Jade – Jadeite E or WCommonlyFairSpecial
 B and IGreen/purple/whiteCommonlyVery good to goodSpecial
 DOccasionallyVariableSpecial
 B and WRarelyPoorSpecial
Jade – NephriteDRarelyUnknownSpecial
KunziteE or HCommonlyFairSpecial
 RCommonlyFairSpecial
Natural
Gemstone
Enhancement
Symbol
Description
Used
Frequency
Encountered
StabilityCare
Requirements
Lapis lazuli E or WCommonlyFairSpecial
 DCommonlyVariableSpecial
MoonstoneNNormal
MorganiteE or HCommonlyExcellentNormal
OpalOWhite/blackRarelyFairSpecial
 IRarelyGoodSpecial
 OBoulderUsuallyGoodSpecial
 DMatrixCommonlyGoodSpecial
 NFire opal *Special
 ICat’s eye UsuallyGoodSpecial
 I/O/DHydrophaneCommonlyGood to fairSpecial
Pearl – Natural E or BWhiteUsuallyVery good Special
 DRarelyVery good to goodSpecial
Pearl – CulturedE or BWhiteUsuallyExcellentSpecial
 DMany colors UsuallyVariableSpecial
 RBlack/grayOccasionallyVery good Special
PeridotE or ORarelyGood to fairSpecial
 FRarelyGoodSpecial
RubyE or HUsuallyExcellentNormal
 FhCommonlyExcellentNormal
 OOccasionallyGood to fairSpecial
 DRarelyPoorSpecial
 RRarelyUnknownNormal
 FCommonlyVery good to fairSpecial
 URarelyGoodSpecial
Natural
Gemstone
Enhancement
Symbol
Description
Used
Frequency
Encountered
StabilityCare
Requirements
SapphireE or HUsuallyExcellentNormal
 UOccasionallyGood to fairSpecial
 OOccasionallyGood to fairSpecial
Sapphire – FancyE or HUsuallyExcellentNormal
 RYellow/orangeOccasionallyVery poorX-Special
 OOccasionallyGood to fairSpecial
 UOccasionallyGood to fairSpecial
SerpentineDVarious colors CommonlyGood to fairSpecial
 E or WCommonlyVery good to goodSpecial
SpinelNNormal
 OOccasionallyGood to fairSpecial
SugeliteNNormal
SunstoneNNormal
TanzaniteE or HUsuallyExcellent*Special
TopazRBlueUsuallyExcellentNormal
 RYellow/orangeOccasionallyVariableSpecial
 RGreenOccasionallyPoorX-Special
 UGreenUsuallyGoodSpecial
 NBrown*Special
 E or HRed/pinkUsuallyExcellentNormal
Natural
Gemstone
Enhancement
Symbol
Description
Used
Frequency
Encountered
StabilityCare
Requirements
TourmalineNChrome green Normal
 NCat’s Eye Normal
 E or HYellow/orangeRarelyExcellentNormal
 RYellow/orangeRarelyVery good Normal
 E or HGreen/blueCommonlyExcellentNormal
 OAny color OccasionallyGood to fairSpecial
 E or HPink/red/purpleOccasionallyExcellentNormal
 RPink/red/purpleCommonlyGoodNormal
 DPink/red/purpleOccasionallyFair to poorSpecial
TurquoiseWCommonlyFair to poorSpecial
 DRarelyPoorX-Special
 ICommonlyGoodSpecial
ZirconNGreen/brown*Special
 E or HBlue/colorlessAlwaysFair to poorSpecial
 E or HYellowRarelyGoodSpecial
 E or HRedCommonlyFair to poorSpecial

Notes:

  • The “N” symbol is used only for gemstones that we guarantee have not been enhanced.
  • All jewelry (with or without stones) requires special care; some jewelry requires extra-special
    (X-Special) care.
  • * Indicates a gemstone that generally requires special or extra-special care (although the need for care is not necessarily related to the enhancement).