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Gemspedia >> Gems >> Gemstone Enhancement

Gemstone Enhancement

Jewels have been objects of desire from the earliest days of mankind. The enduring value of gems and pearls is largely a result of their beauty, durability and rarity. It is this last aspect that has pushed humans to create less expensive alternatives to the natural product. These include imitations such as glass, fully synthetic counterparts of natural gems and enhancements that modify gems and pearls to make them more valuable.

Tanzanite is a gem that would not be available in commercial quantities if it wasn’t heat treated


Certain enhancements have been practised for literally thousands of years. The dying of agate is one example. Others, such as irradiated blue topaz, are solely a product of the technological advances of the modern age.

 

Enhancements have a definite impact on the value of precious stones, with the highest prices paid for natural gems of fine quality that have not been enhanced in any way beyond ordinary cutting and polishing. As a gem is modified to a greater and greater degree, the change in value is also greater. The least expensive gems are those fully made by man (synthetics), because the supply is essentially unlimited. Thus they have limited or no rarity.

What follows is a comprehensive description and discussion of enhancements.

 

Enhancement disclosure

Paraiba Gemstakes enhancement disclosure seriously and, to the best of our ability, provides our clients with complete information on any and all enhancements to which a gem has been subjected. The descriptions we provide below are based upon those of the American Gem Trade Association guidelines (the most stringent in the industry). While many enhancements are currently undetectable, Paraiba Gemsdoes its best to ensure that clients have full access to information for an informed buying decision.

  • Paraiba Gemsdiscloses all known enhancements at the time of sale and backs this up with a 30-day return policy.

  • For most gems today, enhancements are a basic part of the finishing process.

  • While unenhanced gems are the most sought-after, their tremendous rarity and, thus, high prices, put them out of reach of all but the wealthiest of buyers.

  • In order to provide beautiful jewelry to our full spectrum of customers, we offer a broad selection of enhanced gems, in addition to our lines of unenhanced precious stones.

  • The marketplace sets the values of both natural and enhanced gems.

Since certain enhancements are undetectable or difficult to detect, the Paraiba Gems approach is to assume that all items are enhanced unless:

  • There is specific gemological evidence that shows the item has not been enhanced.

  • The item is of a type for which enhancements are not typically used.

We do our best to describe our gems in a clear, consistent and honest fashion. Our approach is to give our customers the same information we would like if we were purchasing the piece. Our mantra is to be true both to our customers and to the precious stones with which we are privileged to work.

 

Definitions

The term enhancement describes any process other than ordinary cutting and polishing that improves the appearance, durability or value of an otherwise natural gemstone or cultured pearl. In today’s gem marketplace, enhanced gems are the rule rather than the exception. Such processes range from simple heating (such as with tanzanite) to high-tech irradiation (such as with blue topaz).

 

Note that an enhancement is, by definition, an artificial process, since it involves human intervention. Thus using a "natural" cedarwood oil to enhance an emerald does not make the process more "natural."

 

There exist several categories of gems, as follows:

  • Fully natural: Stones produced by simply obtaining the raw gem material in nature, cleaning it and then cutting and polishing. With the exception of cleaning and ordinary cutting and polishing, natural gems are fully natural. Examples include natural garnet and peridot.

  • Natural, but enhanced: Stones produced by obtaining the raw gem material in nature, but then processing it in any way beyond normal cleaning, cutting and polishing. Examples include heat-treated sapphire, tanzanite and paraíba tourmaline.

  • Synthetic: Man-made analogs of natural gem materials. In order to qualify as a synthetic, the man-made product must have the same appearance, chemical composition and structure as its natural counterpart. Examples include synthetic ruby and synthetic emerald.

  • Imitation: A gem that has the same appearance as another gem. There are infinite possibilities, including both natural and man-made imitations. Thus natural iolite might imitate a heated tanzanite, while man-made glass might also do the same.

  • Assembled: These are gems made of two or more pieces put together. The pieces can be any combination of natural, synthetic or treated gems. They may be assembled with glue, pressure or even by fusing one piece to another with heat. Examples include opal doublets and triplets and garnet-and-glass doublets.

It should be noted that enhancements are not limited to natural gems. They may also be applied to man-made products.

 

Estimated degree of enhancement

In order to give an estimate of the degree of alteration that a gem has undergone via enhancement, we have created an Estimated Degree of Enhancement Scale. This gives the buyer an idea about the quality of rough prior to treatment. Some processes only lightly enhance a gem, while others have a more significant impact. We use the following scale:

Frequency used

This represents a reasonable estimate of how commonly a particular enhancement process is utilised in the trade, based on a consensus of opinion. Paraiba Gems rates this on the following scale:

Common

Occasional

Rare

Stability

Some enhancements are less stable than others, meaning that the appearance of a gem may change with time. Paraiba Gems rates stability on the following scale:

Good

Fair

Poor

In the event that a gem with less than good stability is offered, Paraiba Gemsdoes their best to make clients aware of the special care needed for that stone. An enhancement is considered stable as long as the gem does not change in appearance or stability under normal wear, cutting, cleaning, repair, or display conditions.

 

Care required

This relates to special care that may be necessary to preserve the effect of the enhancement and/or to preserve the overall look and integrity of the gem. Paraiba Gemsrates this on the following scale:

Normal

Care Needed

Special Caution

Special advice

This addresses the need for any special care required by the specific gemstone variety, irrespective of enhancement.

 

Enhancement categories

The following table shows the enhancements and treatments used for some popular gemstones, their purpose, frequency and care.

  • Natural (N)
    Gems that are, according to best available information, untreated.

  • Enhanced (E)
    Gems that are treated.

 

Codes for specific forms of enhancement

Paraiba Gemsdoes not simply state that a gem has been enhanced, but also tries to give specific information about the enhancement type, according to the following codes:

 

Heat

  • H = Heat Only: Alteration via heat only (or heat + hydrogen). Example: Heated ruby, heated sapphire, heated tanzanite

  • HD = Heat + Diffusion (aka ’bulk’ or ’lattice’ diffusion): Alteration via heat and outside-in diffusion of foreign elements other than hydrogen. Example: Beryllium-diffused sapphire. Paraiba Gemssells beryllium-diffused ruby and sapphire with the "Sunset" prefix.

  • HF = Heat + Flux: Alteration via heat and flux. During heating, fluxes dissolve surface-reaching fissure walls and redeposit that dissolved gem material, healing the fissures closed. Example: Flux-healed ruby (particularly that from Möng Hsu, Burma)

  • HI = Heat + Irradiation: Alteration of color via the use of neutrons, gamma, ultraviolet and/or electron bombardment, followed by heating. Example: Irradiated blue topaz

  • HP = Heat + Pressure: Alteration via heat and pressure. Example: HPHT diamond

Filling

  • F = Filling: Impregnation with a colorless substance. This is typically done to improve clarity, but also improves color, as clarity enhancement facilitates longer light paths within the gem. Fillers include but are not limited to glass, plastic, resin, wax and oil. Some fillers remain fluid at room temperature (and thus are less stable), while others are hardened. Note that any gem with the requisite openings can be filled. Example: Oiled emerald, glass-filled ruby, stabilized turquoise. Paraiba Gemssells glass-filled ruby with the "Kokanada" prefix.

  • FD = Filling + Dye: Impregnation with a colored filler, typically done to add or improve color and possibly also clarity. Note that any gem with the requisite openings can be dyed. Example: Dyed green jadeite

Irradiation

  • I = Irradiation: Alteration of color via the use of neutrons, gamma, ultraviolet and/or electron bombardment. Example: Irradiated morganite

Coating

  • C = Coating: Application of an artificial layer to the surface. Example: Coated diamond, coated topaz

Bleaching

  • B = Bleaching: The use of heat, light and/or chemical agents to lighten or remove color. Subsequent dying and/or filling often accompany this. Example: Bleached cultured pearl, bleached/filled jadeite (’B-jade’)

Laser Drilling

  • L = Laser Drilling: Use of a laser and chemicals to reach and alter inclusions. Example: Laser-drilled diamond

Reconstruction

  • R = Reconstruction: Use of heat, pressure and/or solvents to fuse small pieces of a gem together into a larger whole. Example: Reconstructed amber

Further notes

  • Note that gems may be enhanced by more than one process.

  • The presence or absence of enhancements can have a significant impact on value. Thus it is always a good idea to have major purchases tested by a well-respected gemological lab.

Caring for your gemstone jewelry

Gems are among the most durable of nature’s creations, but still require care if they are to retain their beauty. Caring for your jewelry is a matter of common sense and simple precaution:

  • Always remove your jewelry when engaging in activities that risk impact or exposure to chemicals or heat such as sports or housework.

  • Always put jewelry on after using lotions, cosmetics, hair spray or perfumes, not before.

  • Never remove your jewelry by pulling on the gems.

  • The best way to store your jewelry is in the compartments of a jewelry box or in pouches. Store each piece of gemstone jewelry separately and necklaces flat so that harder stones don’t scratch softer ones. Almost every gem is harder than the metal in which it is set. Gems can scratch one another or the finish on your jewelry if stored carelessly.

  • Carefully wipe jewelry with a soft lint-free cloth after each wearing to remove oils and salts.

  • Clean your jewelry on occasion with a cleaning solution or mechanical cleaner suitable for the gem; use a dish rather than the sink, for if a gem accidentally falls out of the setting, down the drain it goes. When in doubt, just use warm soapy water and a soft toothbrush.

  • Think twice before putting gems in an ultrasonic cleaner. Diamonds and rubies and sapphires are generally fine but many other gems may not be. Thus when in doubt, leave it out.

  • Opaque gems such as lapis lazuli, turquoise and malachite can be porous and may absorb chemicals and soap, discoloring them. Thus they require special care. Never use ultrasonic cleaners, ammonia or chemical solutions. These gem materials should just be wiped clean gently with a moist cloth.

  • Opals also require special care. Never use an ultrasonic, never use ammonia, and avoid heat and strong light that can dry out the water in opals.

  • Organic gems like pearls, coral and amber should only be wiped clean with a moist cloth. Due to their organic nature, these gems are both soft and porous. Be careful about chemicals in hairspray, cosmetics, or perfume; over time they can damage pearls in particular.

  • Stones that have a Mohs hardness of 7 or less are subject to scratching; harder stones are less susceptible, but still subject to chipping and fracture.

For complete care instructions on each gem type, please see the tables below.

 

Mechanical cleaners

The most common mechanical cleaners are ultrasonic and steam cleaners. Ultrasonic cleaners feature two basic parts: a small motor and a cleaning tank. The machine’s motor produces ultrasonic energy that is transmitted with vibrating energy waves (usually 40,000 sound waves per second) to create microscopic bubbles in the cleaning tank. Called cavitation, this motion knocks dirt off the jewelry and is very effective in penetrating the tiny crevices in jewelry that traditional cleaning cloths and topical cleaners cannot easily reach. A steam cleaner uses jets of steam to literally blast dirt off jewelry. As mechanical cleaners can damage some gemstones, always check to see if your gemstone is suitable.

 

Final notes

The following tables show the enhancements used for both major and minor gems, along with care instructions. This has been compiled based on our own experience, coupled with the expertise of our suppliers, the world’s major gemological laboratories, trade associations, regulatory bodies, professional journals, etc. 


Note that enhancements are constantly being developed and altered. We do our best to provide the latest information, but if there are questions, the best solution is to have the individual gem tested by a major gemological laboratory.

Gemstone

Hardness

Code & Degree

Enhancement Method

Freq. Used

Stability

Care Req’d

Special Advice

Agate
(see
 Quartz-Chalcedony)

 

 

 

 

 

 

 

Alexandrite
(see
 Chrysoberyl)

 

 

 

 

 

 

 

Amazonite
(see
 Feldspar)

 

 

 

 

 

 

 

Amber

2-2.5

 

 

 

 

 

The skin of amber may naturally darken with age. Thus repolishing may produce a lightening of color.

All varieties

 

H/L

Heated to improve appearance

Common

Good

Care needed

Avoid heat, steaming, chemicals and ultrasonic

 

 

FD/S

Dyed to improve appearance

Rare

Variable

Care needed

Avoid repolishing, heat, steaming, chemicals and ultrasonic

 

 

R/S

Heated under pressure to fuse small pieces into a larger piece

Common

Good

Care needed

Avoid heat, steaming, chemicals and ultrasonic

Green

 

HP/S

Heated under pressure to induce a green color

Common

Good

Care needed

Avoid heat, steaming, chemicals and ultrasonic

Amblygonite / Montebrasite

5.5-6

I

Irradiated to improve color

Common

Good to Fair

Care needed

May be prone to thermal shock; avoid extreme temperature changes

Amethyst
(see
 Quartz)

 

 

 

 

 

 

 

Ametrine
(see
 Quartz)

 

 

 

 

 

 

 

Ammolite

4

 

 

 

 

 

 

All varieties

 

F/M

Impregnated with colorless hardened filler to improve appearance and durability

Common

Good to Fair

Care needed

Avoid heat, steaming, chemicals and ultrasonic; may not be suitable for re-cutting or re-polishing

Andesine
(see
 Feldspar)

 

 

 

 

 

 

 

Andalusite

6.5-7.5

N

None

-

-

Care needed

Avoid boiling and ultrasonic cleaning

Apatite

5

H/L

Heated to improve appearance

Common

Good

Care needed

Avoid heat, steaming, chemicals and ultrasonic; somewhat soft; brittle; handle with care

Aquamarine
(see
 Beryl)

 

 

 

 

 

 

 

Aventurine
(see
 Quartz)

 

 

 

 

 

 

 

Azurite (includes Azurmalachite)

3.5-4

 

 

 

 

 

 

All varieties except druzy

 

F/L-M

Dipped in colorless wax to improve appearance; impregnated with colorless hardened or unhardened filler to improve appearance and durability

Common

Good to Fair

Care needed

Avoid heat, steaming, chemicals and ultrasonic

Druzy

 

N

None

-

Good

Care needed

Brittle; avoid shock

Beryl

7.5-8

 

 

 

 

 

 

Aquamarine

 

H/L

Heated to improve color

Common

Good

Care needed

Avoid sudden temperature changes, heat, steaming, chemicals and ultrasonic

Blue
(’maxixe’ type)

 

I/S

Irradiated blue from pale pink to colorless

Always

Poor

Special caution

Color fades; avoid light and heat

Colorless
(aka ’fire’ or ’goshenite’)

 

N

None

-

-

Care needed

Avoid sudden temperature changes, heat, steaming, chemicals and ultrasonic

Emerald

 

F/L-M

Impregnated with colorless hardened or unhardened filler to improve appearance

Common

Fair

Care needed

Avoid sudden temperature changes, heat, steaming, chemicals and ultrasonic

 

 

FD/L-S

Dyed with hardened or unhardened filler to improve appearance

Occasional

Fair

Care needed

Avoid sudden temperature changes, heat, steaming, chemicals and ultrasonic

Pink
(aka ’morganite’)

 

I + H/L

Irradiation followed by heating to improve color

Common

Good

Care needed

Avoid sudden temperature changes, heat, steaming, chemicals and ultrasonic; rarely may fade in light or heat

Red emerald
(aka ’bixbite’)

 

F/L-S

Impregnated with colorless hardened or unhardened filler to improve appearance

Common

Fair

Care needed

Avoid sudden temperature changes, heat, steaming, chemicals and ultrasonic

Yellow & golden
(aka ’heliodor’), green beryl

 

I/M

Irradiated to improve color

Common

Variable

Care needed

Certain stones may fade in light or heat

Bixbite
(see
 Beryl)

 

 

 

 

 

 

 

Bloodstone
(see
 Quartz-Chalcedony)

 

 

 

 

 

 

 

Brazilianite

5.5

N

None

-

-

Care needed

Fragile; handle with care; avoid heat, steaming, chemicals and ultrasonic

Carnelian
(see
 Quartz-Chalcedony)

 

 

 

 

 

 

 

Chalcedony 
(see
 Quartz-Chalcedony)

 

 

 

 

 

 

 

Charoite

5-6

N

None

-

-

Care needed

Avoid heat, steaming, chemicals and ultrasonic

Chrysoberyl

8.5

 

 

 

 

 

 

Alexandrite

 

F/L-M

Impregnated with colorless filler to improve appearance

Rare

Fair

Care needed

Avoid sudden temperature changes, heat, steaming, chemicals and ultrasonic

Cat ’s eye

 

I/S

Irradiated to improve color

Rare

Good

Special caution

If neutron irradiated, refer to the NRC for safety requirements

Chrysocolla

2-4 (or more, if mixed with quartz)

F/M-S

Impregnated with colorless filler to improve appearance and durability

Common

Fair

Care needed

Avoid heat, steaming, chemicals and ultrasonic

Chrysoprase
(see
 Quartz-Chalcedony)

 

 

 

 

 

 

 

Citrine
(see
 Quartz)

 

 

 

 

 

 

 

Clinohumite

6

N

None

-

-

Normal

-

Coral

3.5-4

 

 

 

 

 

 

Black

 

N

None

-

-

Care needed

Avoid heat, steaming, chemicals and ultrasonic

White

 

B/L

Bleached to improve appearance

Common

Fair

Care needed

Avoid heat, steaming, chemicals and ultrasonic; may discolor over time

Pink, orange

 

F/L

Impregnated with colorless filler to improve appearance and durability

Common

Fair

Care needed

Avoid heat, steaming, chemicals and ultrasonic

Red

 

FD/M-S

Dyed to improve appearance

Common

Fair

Care needed

May fade in light or heat; avoid heat, steaming, chemicals and ultrasonic

Gold

 

B/S

Bleached from black coral

Common

Good

Care needed

Avoid heat, steaming, chemicals and ultrasonic

Corundum

9

 

 

 

 

 

 

Ruby and sapphire of all types

 

H/L-S

Heated to improve appearance

Common

Good

Normal

-

 

 

HF/M-S

Heated with flux to improve appearance and durability

Common

Good

Normal

-

Ruby & sappire (aka "Sunset" ruby & sapphire)

 

HD/S

Heated with elements other than hydrogen to improve color and/or add asterism

Common

Good

Normal

If diffused layer is just at the surface, avoid repolishing

 

 

F/M-S

Surface pits filled with colorless hardened filler to improve appearance and/or add weight

Occasional

Fair

Care needed

Avoid heat, steaming, chemicals and ultrasonic

 

 

FD/S

Dyed to improve appearance

Rare

Fair

Care needed

Avoid heat, steaming, chemicals and ultrasonic

Ruby (aka ’Kokanada ruby’)

 

FD/S

Impregnated with colorless or colored lead glass filler to improve appearance; sometimes classified as composite gemstones, these rubies are treated using heat and a high refractive index lead-glass to fill fractures and cavities. This vastly improves the apparent clarity and potentially adds weight and/or intensifies color and/or color uniformity and/or appearance. The lead-glass is typically yellow to orange in color and can artificially augment the red color of these gems.

Common

Fair

Care needed

Avoid heat, steaming, chemicals and ultrasonic. Fillers in cavities and/or fissures can scratch more easily than the host gem or be more vulnerable to damage from heat or some chemicals. The lead glass may be damaged by a variety of solvents.

Yellow and orange sapphire

 

I/S

Irradiated to alter color

Rare

Poor

Care needed

Color fades with exposure to light and/or heat

Danburite

7-7.5

 

 

 

 

 

 

Colorless, pink, yellow

 

N

None

-

-

Normal

-

Brown

 

I/S

Irradiated to improve color

Common

Unknown

Care needed

May fade; avoid prolonged exposure to heat and light

Diamond

10

 

 

 

 

 

 

All varieties

 

L/M

Laser drilled to improve appearance

Occasional to Common

Good

Normal

-

 

 

C/S

Coated to improve appearance

Occasional

Good to Poor, depending on method

Special caution

Recutting, steaming, ultrasonic and occasionally alcohol may adversely affect color and appearance

 

 

F/S

Impregnated with hardened colorless filler to improve appearance

Occasional

Good

Care needed

Recutting, steaming, ultrasonic or extreme heat may remove filler

 

 

HP/S

Heated under pressure to improve appearance

Rare

Good

Normal

Recutting or extreme heat may remove filler

 

 

I/S

Irradiated and/or heated to induce fancy colors

Common

Good

Normal, except green

Avoid heating irradiated green stones as the color may change; some green stones have been radium irradiated; for safety requirements, refer to the NRC

 

 

C/S

Coated to produce fancy colors

Rare

Fair to Poor

Care needed

Recutting or extreme heat may damage coating

Diaspore

6.5-7

 

 

 

 

 

 

Zultanite

 

N

None

-

-

Care needed

Avoid heat, steaming, chemicals and ultrasonic

Diopside

5.5-6.5

 

 

 

 

 

 

Chrome, star, cat’s eye

 

N

None

-

-

Care needed

Avoid heat, steaming, chemicals and ultrasonic

Emerald
(see
 Beryl)

 

 

 

 

 

 

 

Enstatite

5-6

N

None

-

-

Care needed

Avoid heat, steaming, chemicals and ultrasonic

Epidote

6-7

N

None

-

-

Care needed

Avoid heat, steaming, chemicals and ultrasonic

Euclase

7.5

N

None

-

-

Care needed

Brittle; avoid heat, steaming, chemicals and ultrasonic

Feldspar

6

 

 

 

 

 

 

Microcline (aka ’amazonite’)

 

F/M

Impregnated with colorless hardened or unhardened filler to improve appearance

Common

Good to Fair

Care needed

Avoid heat, steaming, chemicals and ultrasonic

Andesine (aka ’sunstone’)

 

HD/S

Heated with Cu to improve appearance

Common

Good to Fair

Care needed

Avoid heat, steaming, chemicals and ultrasonic

Labradorite (aka ’sunstone’)

 

HD/S

Heated with Cu to improve appearance

Common

Good

Care needed

Avoid heat, steaming, chemicals and ultrasonic

Labradorite (aka ’spectrolite’)

 

F/M

Impregnated with colorless hardened or unhardened filler to improve appearance

Occasional

Good to Fair

Care needed

Avoid heat, steaming, chemicals and ultrasonic

Labradorite (aka ’Oregon sunstone’)

 

N

None

-

-

Care needed

Avoid heat, steaming, chemicals and ultrasonic

Orthoclase (aka ’moonstone’)

 

N

None

-

-

Care needed

Avoid heat, steaming, chemicals and ultrasonic

Oligoclase (aka ’sunstone’)

 

N

None

-

-

Care needed

Avoid heat, steaming, chemicals and ultrasonic

Fluorite

4

 

 

 

 

 

 

 

 

I/M

Irradiated to improve color

Common

Fair

Care needed

Both naturally colored and irradiated fluorites may fade upon prolonged exposure to light; soft and brittle; handle with care; avoid heat, steaming, chemicals and ultrasonic

Gahnite
(see
 Spinel)

 

 

 

 

 

 

 

Garnet

6.5-7.5

 

 

 

 

 

 

All types except demantoid

 

N

None

-

-

Care needed

Avoid sudden temperature changes; avoid heat, steaming, chemicals and ultrasonic

Demantoid

 

H/L

Heated to improve color

Common

Good

Care needed

Avoid sudden temperature changes; avoid heat, steaming, chemicals and ultrasonic

Heliodor
(see
 Beryl)

 

 

 

 

 

 

 

Hematite

5-6.5

N

None

-

-

Care needed

Brittle

Hiddenite
(see
 Spodumene)

 

 

 

 

 

 

 

Idocrase
(see
 Vesuvianite)

 

 

 

 

 

 

 

Iolite (aka ’Tanolite’ or ’Cordierite’)

7-7.5

N

None

-

-

Care needed

Avoid thermal shock; damaged by acids

Ivory & Bone

 

 

 

 

 

 

 

All varieties

 

B/L

Bleached to whiten and remove discoloration

Common

Good

Care needed

Avoid heat, steaming, chemicals and ultrasonic; may discolor over time

 

 

FD/M-S

Dyed to improve appearance

Occasional

Good

Care needed

Avoid heat, steaming, chemicals and ultrasonic; may discolor over time

 

 

F/M-S

Impregnated with colorless hardened or unhardened filler to improve appearance

Occasional

Good

Care needed

Avoid heat, steaming, chemicals and ultrasonic; may discolor over time

 

 

B + F/M-S

Two-step bleaching and colorless impregnation to improve appearance

Common

Good to Fair

Care needed

Avoid heat, steaming, chemicals and ultrasonic; may discolor over time

 

 

B + FD/S

Two-step bleaching and dying to improve appearance

Common

Good to Fair

Care needed

Avoid heat, steaming, chemicals and ultrasonic; may fade with time

 

 

FD/S

Dyed to improve appearance; dye may be selective in coverage

Common

Good to Fair

Care needed

Avoid heat, steaming, chemicals and ultrasonic; may fade with time

 

 

H/L

Heated to intensify brown/orange color

Common

Good

Care needed

Avoid heat, steaming, chemicals and ultrasonic

 

 

H/L

Heated with or without chemicals to simulate age

Occasional

Good

Care needed

Avoid heat, steaming, chemicals and ultrasonic

Jadeite Jade

6.5-7

 

 

 

 

 

 

All varieties

 

F/L

Dipped in colorless wax to improve appearance

Always

Fair

Care needed

Avoid heat, steaming, chemicals and ultrasonic

 

 

B + F/S

Two-step bleaching and colorless impregnation to improve appearance

Common

Good to Fair

Care needed

Avoid heat, steaming, chemicals and ultrasonic

 

 

B + FD/S

Two-step bleaching and dying to improve appearance

Common

Good to Fair

Care needed

Avoid heat, steaming, chemicals and ultrasonic; may fade with time

 

 

FD/S

Dyed to improve appearance; dye may be selective in coverage

Common

Good to Fair

Care needed

Avoid heat, steaming, chemicals and ultrasonic; may fade with time

 

 

H/M

Heated to intensify brown/orange color

Common

Good

Care needed

Avoid heat, steaming, chemicals and ultrasonic

Jasper
(see
 Quartz-Chalcedony)

 

 

 

 

 

 

 

Kornerupine

6.5-7

N

None

-

-

Care needed

Brittle; handle with care

Kunzite
(see
 Spodumene)

 

 

 

 

 

 

 

Kyanite

4-7

N

None

-

-

Care needed

Somewhat brittle and softer in one direction; handle with care

Labradorite
(see
 Feldspar)

 

 

 

 

 

 

 

Lapis Lazuli

5-6

 

 

 

 

 

 

All varieties

 

FD/S

Dyed to improve appearance

Common

Fair

Care needed

Avoid heat, steaming, chemicals and ultrasonic; may fade with time

 

 

F/M

Coated or impregnated with colorless filler to improve appearance and durability

Rare

Good to Fair

Care needed

Avoid heat, steaming, chemicals and ultrasonic

Larimar
(see
 Pectolite)

 

 

 

 

 

 

 

Malachite

3.5-4.5

F/M

Impregnated with colorless hardened or unhardened filler to improve appearance

Occasional

Good to Fair

Care needed

Avoid heat, steaming, chemicals and ultrasonic

Marcasite

6-6.5

N

None

-

-

Care needed

Brittle; handle with care

Maw-sit-sit

6-8

N

None

-

-

Care needed

Avoid heat, steaming, chemicals and ultrasonic

Moldavite
(see
 Tektite)

 

 

 

 

 

 

 

Montebrasite
(see
 Amblygonite)

 

 

 

 

 

 

 

Mookite
(see
 Quartz-Chalcedony, Jasper)

 

 

 

 

 

 

 

Moonstone
(see
 Feldspar)

 

 

 

 

 

 

 

Morganite
(see
 Beryl)

 

 

 

 

 

 

 

Mother-of-pearl
(see
 Pearl)

 

 

 

 

 

 

 

Nephrite Jade

6-6.5

 

 

 

 

 

 

All varieties

 

FD/S

Dyed to improve appearance; dye may be selective in coverage

Common

Good to Fair

Care needed

Avoid heat, steaming, chemicals and ultrasonic; may fade with time

Cat’s eye

 

N

None

-

-

Care needed

Avoid heat, steaming, chemicals and ultrasonic

Obsidian

5-6

N

None

-

-

Care needed

Heat sensitive and brittle

Oligoclase
(see
 Feldspar)

 

 

 

 

 

 

 

Onyx
(see
 Quartz-Chalcedony)

 

 

 

 

 

 

 

Opal

5.5-6.5

 

 

 

 

 

 

All varieties except fire opal

 

F/S

Impregnated with colorless hardened or unhardened filler to improve appearance and/or durability

Occasional

Fair

Care needed

Avoid heat, steaming, chemicals and ultrasonic

Matrix

 

FD/S

Dyed via sugar solution infilling, then acid bath to dye background and enhance color play and intensity

Common

Good

Care needed

Avoid heat, steaming, chemicals and ultrasonic

Fire opal & moss opal

 

N

None

-

-

Care needed

Avoid heat, steaming, chemicals and ultrasonic

Pearl, Natural and Cultured

2.5-4.5

 

 

 

 

 

 

All varieties, including mother-of-pearl

 

FD/L-S

Dyed to improve color. May include use of colored nuclei and/or heat

Common

Fair

Care needed

Avoid exposure to UV light, heat, steaming, chemicals and ultrasonic

 

 

B/L

Bleached to improve color and appearance

Common

Good

Care needed

Avoid exposure to UV light, heat, steaming, chemicals and ultrasonic

 

 

C/M

Coated to improve appearance

Occasional

Fair

Care needed

Avoid exposure to UV light, heat, steaming, chemicals and ultrasonic

 

 

I/S

Irradiated to improve color

Occasional

Good

Care needed

Avoid exposure to UV light, heat, steaming, chemicals and ultrasonic

Pectolite (aka ’Larimar’)

4.5-5

N

None

-

-

Care needed

Somewhat soft; handle with care

Peridot

6.5-7

N

None

-

-

Care needed

Avoid heat, steaming, chemicals and ultrasonic

All varieties

 

H/L

Heated to improve color

Occasional

Good

Care needed

Avoid heat, steaming, chemicals and ultrasonic

 

 

F/L

Impregnated with colorless hardened or unhardened filler to improve appearance and/or durability

Occasional

Fair

Care needed

Avoid heat, steaming, chemicals and ultrasonic

Petalite

6-6.5

N

None

-

-

Care needed

Brittle; handle with care

Pezzottaite

8

F/L-S

Impregnated with colorless hardened or unhardened filler to improve appearance and/or durability

Occasional

Fair

Care needed

Avoid sudden temperature changes, heat, steaming, chemicals and ultrasonic

Phenakite

7.5-8

N

None

-

-

Care needed

Brittle; handle with care

Prehnite

6-6.5

N

None

-

-

Care needed

Brittle; handle with care

Pyrite

6-6.5

N

None

-

-

Care needed

Brittle and heat sensitive; handle with care

Quartz

7

 

 

 

 

 

 

Cat’s eye, rutilated, tourmalinated, rose, rock crystal

 

N

None

-

-

Normal

-

Amethyst

 

H/L

Heated to improve color

Occasional

Good

Care needed

Whether treated or not, may fade with prolonged exposure to light or heat

Ametrine, translucent blue (aka ’blue moon’), green (aka ’prase’ or ’prasiolite’)

 

H/L

Heated to improve color

Common

Good

Care needed

Whether treated or not, may fade with prolonged exposure to light or heat

Citrine

 

H/S

Produced by heating various types of quartz

Common

Good

Care needed

Whether treated or not, may fade with prolonged exposure to light or heat

Amethyst, green (aka ’prase’ or ’prasiolite’), lemon quartz, smoky quartz, blueberry quartz

 

I/M

Irradiated to improve color

Common

Fair

Care needed

May fade in light or heat; avoid heat, steaming, chemicals and ultrasonic

Quartz-Chalcedony (aka ’Cryptocrystalline’ Quartz)

6.5-7

 

 

 

 

 

 

Agate, banded, blue, green, jasper

 

FD/S

Dyed to improve appearance

Common

Good to Fair

Care needed

May fade in light or heat; avoid heat, steaming, chemicals and ultrasonic

Black (onyx)

 

H/S

Impregnated/acid treated to alter color

Always

Good

Care needed

May fade in light or heat; avoid heat, steaming, chemicals and ultrasonic

Carnelian, sard; sardonyx

 

FD/S

Dyed to improve appearance

Occasional

Good to Fair

Care needed

May fade in light or heat; avoid heat, steaming, chemicals and ultrasonic

 

 

H/M

Heated to improve appearance

Common

Good

Normal

-

Chrysoprase, bloodstone

 

N

-

-

-

Normal

-

Quartzite & Microcrystalline Quartz

6.5-7

 

 

 

 

 

 

Aventurine

 

FD/S

Dyed to improve color

Common

Fair

Care needed

Dye may fade; avoid heat, steaming, chemicals and ultrasonic

Black

 

I/M

Irradiated to improve color

Common

Good

Care needed

May fade in light or heat; avoid heat, steaming, chemicals and ultrasonic

Other quartzite

 

FD/S

Dyed to improve or completely change color

Common

Fair

Care needed

Dye may fade; avoid heat, steaming, chemicals and ultrasonic

Tiger’s eye

 

H/L

Heated to improve color

Common

Good

Normal

-

 

 

B/L

Bleached to improve color

Common

Good

Normal

-

 

 

FD/S

Dyed to improve or completely change color

Common

Fair

Care needed

Dye may fade; avoid heat, steaming, chemicals and ultrasonic

Rhodonite

5.5-6.5

 

 

 

 

 

 

All varieties

 

FD/S

Dyed to produce various colors

Common

Fair

Care needed

Dye may fade; avoid heat, steaming, chemicals and ultrasonic

Ruby
(see
 Corundum)

 

 

 

 

 

 

 

Sapphire
(see
 Corundum)

 

 

 

 

 

 

 

Sard
(see
 Quartz-Chalcedony)

 

 

 

 

 

 

 

Scapolite

6

N

None

-

-

Care needed

Brittle; handle with care; yellow gems may fade in light or heat

Serpentine

4-6

 

 

 

 

 

 

All varieties

 

F/M

Impregnated with colorless filler to improve appearance

Common

Good to Fair

Care needed

Avoid heat, steaming, chemicals and ultrasonic

 

 

FD/S

Dyed to alter color

Rare

Fair

Care needed

Dye may fade; avoid heat, steaming, chemicals and ultrasonic

Shell

4

 

 

 

 

 

 

Pink

 

FD/S

Dyed to improve color

Common

Fair

Care needed

Dye may fade; avoid heat, steaming, chemicals and ultrasonic

Sillimanite (Fibrolite)

6--7

N

None

-

-

Care needed

Brittle; handle with care

Sodalite

5.5-6

FD

Dyed to improve color

Rare

Fair

Care needed

Dye may fade; avoid heat, steaming, chemicals and ultrasonic

Spectrolite
(see
 Feldspar-Labradorite)

 

 

 

 

 

 

 

Sphene

5-5.5

N

None

-

-

Care needed

Soft and brittle; handle with care; avoid heat, steaming, chemicals and ultrasonic

Spinel

7.5-8

 

 

 

 

 

 

All varieties

 

F/L-M

Impregnated with colorless filler to improve appearance

Rare

Fair

Care needed

Avoid heat, steaming, chemicals and ultrasonic

Spodumene

6.5-7.5

 

 

 

 

 

 

Kunzite

 

H/L

Heated to improve color

Common

Fair

Care needed

Natural and/or treated material may fade; avoid heat, strong light, ultrasonic

 

 

I/M

Irradiated and heated to improve color

Common

Fair

Care needed

Natural and/or treated material may fade; avoid heat, strong light, ultrasonic

Green (aka ’hiddenite’) and yellow

 

I/S

Irradiated to produce green color

Rare

Poor

Special caution

Color fades in light or heat

Sugilite

6-6.5

N

-

-

-

Care needed

Avoid heat, steaming, chemicals and ultrasonic

Sunstone
(see
 Feldspar)

 

 

 

 

 

 

 

Tanolite
(see
 Iolite)

 

 

 

 

 

 

 

Tanzanite
(see
 Zoisite)

 

 

 

 

 

 

 

Tektite

5.5-6.5

 

 

 

 

 

 

Brown, green (aka ’moldavite’)

 

N

None

-

-

Care needed

Brittle; handle with care

Topaz

8

 

 

 

 

Care needed

Somewhat brittle; handle with care

Blue

 

HI/S

Irradiated to a brown color, followed by heating to blue

Common

Good

Care needed

If neutron irradiated to produce blue color, refer to NRC for safety requirements; somewhat brittle; handle with care

Brown, yellow, orange

 

H/L

Heated to improve color

Common

Good

Care needed

Somewhat brittle; handle with care

Pink, red, orange

 

I/M

Irradiated to improve color

Occasional

Poor

Special caution

Color fades in light or heat; somewhat brittle; handle with care

All colors

 

C/S

Coated in various colors

Common

Fair

Care needed

Avoid repolishing, which removes coating; some coatings also damaged by chemicals and ultrasonic; somewhat brittle; handle with care

Tourmaline

7-7.5

 

 

 

 

 

 

Various colors

 

H/L

Heated to improve color

Common

Good

Care needed

Avoid heat, steaming, chemicals and ultrasonic

 

 

I/L-M

Irradiated to improve color

Common

Good

Care needed

Avoid heat, steaming, chemicals and ultrasonic

 

 

F/L-M

Impregnated with colorless filler to improve appearance

Occasional

Fair

Care needed

Avoid heat, steaming, chemicals and ultrasonic

 

 

FD/S

Dyed to improve color

Rare

Fair

Care needed

May fade in light or heat; avoid heat, steaming, chemicals and ultrasonic

Turquoise

5-6

 

 

 

 

 

 

All varieties

 

F + I/S

Impregnated with colorless filler to improve appearance and durability; irradiation may be used to harden filler

Common

Good to Fair

Care needed

Avoid heat, steaming, chemicals and ultrasonic

 

 

FD/S

Dyed to improve color

Rare

Fair

Care needed

Avoid heat, steaming, chemicals and ultrasonic

Vesuvianite
(aka Idocrase)

6-7

N

None

-

-

Normal

-

<PZircon

6.5-7.5

 

 

 

 

 

 

Blue, yellow, orange, green, colorless

 

H/L-S

Heated to improve color

Common

Fair

Care needed

Color may fade with time; can be restored by reheating

Zoisite

6-7

 

 

 

 

 

 

Tanzanite, green tanzanite & chameleon tanzanite

 

H/L-S

Heated to improve color

Common

Good

Care needed

Avoid sudden temperature changes, heat, steaming, chemicals and ultrasonic

Tanzanite

 

C/S

Coated to improve color

Rare

Fair

Care needed

Avoid repolishing, which removes coating; some coatings also damaged by chemicals and ultrasonic

Zultanite
(see
 Diaspore)

 

 

 

 

 

 

 


Gem Enhancement & Care Chart-Other Gems

Gemstone

Hardness

Code & Degree

Enhancement Method

Fre. Used

Stability

Care Req’d

Special Advice

Anatase

5.5-6

N

None

-

-

Care needed

Avoid chemicals and ultrasonic

Anglesite

2.5-3

N

None

-

-

Care needed

Avoid chemicals and ultrasonic; brittle and soft; avoid thermal and physical shock

Apophyllite

4.5-5

N

None

-

-

Care needed

Avoid chemicals and ultrasonic; brittle and soft; avoid thermal and physical shock

Aragonite

3.5-4

N

 

 

 

 

 

Axinite

6-7

N

None

-

-

Care needed

Brittle; avoid shock

Barite

2.5-3.5

N

None

-

-

Care needed

Fragile; handle with care

Bastnäsite

4-4.5

N

None

-

-

Care needed

Fragile; handle with care

Boracite

7-7.5

N

None

-

-

Normal

-

Burbankite

3.5-4

N

None

-

-

Care needed

Fragile; handle with care

Bustamite

5.5-6.5

N

None

-

-

Care needed

Fragile; handle with care

Calcite

3

N

None

-

-

Care needed

Fragile; handle with care

Cassiterite

6-7

N

None

-

-

Care needed

Brittle; handle with care

Celestite

3-3.5

N

None

-

-

Care needed

Fragile; handle with care

Cinnabar

2-2.5

N

None

-

-

Care needed

Fragile; handle with care

Creedite

4

N

None

-

-

Care needed

Fragile; handle with care

Datolite

5-5.5

N

None

-

-

Care needed

Somewhat fragile; handle with care

Dolomite

3.5-4

N

None

-

-

Care needed

Fragile; handle with care

Dumortierite

7-8.5

N

None

-

-

Normal

-

Ekanite

5-6.5

N

None

-

-

Special caution

May be radioactive; should not be worn in jewellery or kept near skin

Eosphorite

5

N

None

-

-

Care needed

Somewhat soft; handle with care

Euclase

7.5

N

None

-

-

Care needed

Brittle; avoid heat, steaming, chemicals and ultrasonic

Eudialyte

5-5.5

N

None

-

-

Care needed

Somewhat soft; handle with care

Genthelvite

6-6.5

N

None

-

-

Normal

-

Haüyne

5.5-6

N

None

-

-

Care needed

Fragile; handle with care

Hemimorphite

5

N

None

-

-

Care needed

Somewhat soft; handle with care

Herderite

5-5.5

N

None

-

-

Care needed

Somewhat soft; handle with care

Howlite

3-3.5

 

 

 

 

 

 

Blue

 

FD/S

Dyed to improve color

Always

Good to Fair

Care needed

Avoid heat, steaming, chemicals and ultrasonic; may fade over time; Somewhat soft; handle with care

White

 

N

None

-

-

Care needed

Somewhat soft; handle with care

Leifite

6

N

None

-

-

Care needed

Brittle; handle with care

Leucite

5.5-6

N

None

-

-

Care needed

Brittle; handle with care

Manganotantalite

5.5-6.5

N

None

-

-

Care needed

Somewhat brittle; handle with care

Mellite

2-2.5

N

None

-

-

Care needed

Soft and brittle; handle with care; avoid heat, steaming, chemicals and ultrasonic

Milarite

5.5-6

N

None

-

-

Care needed

Brittle; handle with care

Monazite

5-5.5

N

None

-

-

Special caution

May be radioactive; should not be worn in jewellery or kept near skin

Natrolite

5-5.5

N

None

-

-

Care needed

Soft and brittle; handle with care; avoid heat, steaming, chemicals and ultrasonic

Nuumit (Nuumite)

5-6

N

None

-

-

Normal

-

Painite

8

N

None

-

-

Normal

-

Parisite

4.5

N

None

-

-

Care needed

Soft and brittle; handle with care; avoid heat, steaming, chemicals and ultrasonic

Pollucite

6.5-7

N

None

-

-

Care needed

Brittle; handle with care

Poudretteite

5

N

None

-

-

Care needed

Somewhat soft; handle with care

Pyroxmangite

5.5-6

N

None

-

-

Care needed

Brittle; handle with care

Remondite

3-3.5

N

None

-

-

Care needed

Soft and brittle; handle with care; avoid heat, steaming, chemicals and ultrasonic

Rhodochrosite

3.5-4

N

None

-

-

Care needed

Soft and brittle; handle with care; avoid heat, steaming, chemicals and ultrasonic

Rhodonite

5.5-6.5

 

 

 

 

 

 

All varieties

 

FD/S

Dyed to produce various colors

Common

Fair

Care needed

Dye may fade; avoid heat, steaming, chemicals and ultrasonic

Rutile

6-6.5

N

None

-

-

Care needed

Brittle; handle with care

Scheelite

4.5-5

N

None

-

-

Care needed

Soft and brittle; handle with care; avoid heat, steaming, chemicals and ultrasonic

Scolecite

5-5.5

N

None

-

-

Care needed

Soft and brittle; handle with care; avoid heat, steaming, chemicals and ultrasonic

Sellaite

5-5.5

N

None

-

-

Care needed

Brittle; handle with care

Senarmontite

2-2.5

N

None

-

-

Care needed

Soft and brittle; handle with care; avoid heat, steaming, chemicals and ultrasonic

Serandite

4.5-5

N

None

-

-

Care needed

Soft and brittle; handle with care; avoid heat, steaming, chemicals and ultrasonic

Shortite

3

N

None

-

-

Care needed

Soft and brittle; handle with care; avoid heat, steaming, chemicals and ultrasonic

Siderite

4

N

None

-

-

Care needed

 

Sinhalite

6.5-7

N

None

-

-

Normal

-

Smithsonite

4-5

N

None

-

-

Care needed

Soft and brittle; handle with care; avoid heat, steaming, chemicals and ultrasonic

Sphalerite

3.5-4

N

None

-

-

Care needed

Soft and brittle; handle with care; avoid heat, steaming, chemicals and ultrasonic

Staurolite

7-7.5

N

N

-

-

Care needed

Brittle; handle with care

Thaumasite

3.5

N

None

-

-

Care needed

Brittle; handle with care

Thomsonite

5-5.5

N

None

-

-

Care needed

Soft and brittle; handle with care; avoid heat, steaming, chemicals and ultrasonic

Titanium

7

 

 

 

 

 

 

Druzy

 

C/S

Coated to produce rainbow effect

Common

Good

Normal

-

Tremolite

5-6

N

None

-

-

Care needed

Brittle; handle with care

Unakite

6-7

N

None

-

-

Normal

-

Villiaumite

2-2.5

N

None

-

-

Care needed

Soft and brittle; handle with care; avoid heat, steaming, chemicals and ultrasonic

Willemite

5.5

 

 

 

 

 

 

Blue

 

H/S

Heated to change color from white to blue

Rare

Unknown

Care needed

Brittle; handle with care

Wilsonite

3-4

N

None

-

-

Care needed

Soft and brittle; handle with care; avoid heat, steaming, chemicals and ultrasonic

Wulfenite

2.5-3

N

None

-

-

Care needed

Soft and brittle; handle with care; avoid heat, steaming, chemicals and ultrasonic


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