Gemstone Enhancements and Treatments

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Namaskaar

 

Found a nice article on Gemstone Enhancements and Treatment: A cut-paste

follows:

 

Thanks and Regards

Bharat

 

GEMSTONE TREATMENTS

 

The treatment and enhancement of gemstones has existed for hundreds of

years. Some enhancements improve on nature, cannot be detected and are

permanent; this provides the gem market with a larger supply of beautiful

gemstones. Other treatments produce dramatic changes in the gemstone itself

or it's clarity; the irradiation and heating of colorless topaz that

permanently transforms it into blue topaz is an excellent example. A few

treatments are less stable and should be avoided by the knowledgeable buyer.

Following is a description of some common treatments. This is just the tip

of the iceberg. Please refer to the recommended reading list at the bottom

of the page for further information.

 

Most often, treatments of gemstones are done by the cutter. The lapidary

wants the value of the finished product to be as high as possible.

Occasionally treatments are performed on the stones before getting to the

cutter. The heat treatment of corundum (rubies and sapphires) is an

excellent example. The heat treatments of corundum are routinely done where

the stone is mined, before cutting, and may not be disclosed to the lapidary

before cutting is done.

 

Treatments and Pricing

There are some gemstones that would not even exist if it were not for

treatments. The abundance of citrine, in shades of yellow, gold and orange

is the result of heat treating amethyst. Naturally occurring citrine is

quite rare in nature. If it was not for treatments the stone would be far

more expensive than it is!

Tanzanite in shades of violet and blue depends on heat treatment to produce

enough supply to meet the demands of the public.

Pink topaz is another example of a gem that would not be available without

heat treatment. Not only are these treatments acceptable, they are necessary

to keep these products affordable and available.

Recent demand for unheated sapphires and rubies has caused a price increase

of as much as 50%-100% for unheated material. Does this mean that the

untreated gem is more beautiful? NO! In most cases the heating enhances the

gemstone to make it more beautiful.

 

Heating

Heating is the most common treatment available. It can cause the color of a

stone to lighten, darken, or change completely. It can bring about an

improvement in clarity and brightness. Heating is detectable only by trained

observers in a laboratory setting and is usually irreversible under normal

conditions. Unheated rubies and sapphires will contain microscopic rutile

needles or tiny gas bubbles in pockets of liquid which are evidence that

laboratories can use to guarantee that these stones have not been heated. If

these gems are the finest color they will command premium prices due to

their extreme rarity.

 

The following gems are routinely heat treated:

tanzanite

citrine

pink topaz

aquamarine

ruby

sapphire

zircon (both blue and colorless)

 

Oiling

Oiling of emerald is universal, but not EVERY emerald is oiled, (fine

untouched specimens will command astronomical prices). When the rough

emerald is mined it is thrown into a barrel of oil; when it is cut, oil is

used as a lubricant on the cutter's lap. The colorless oil seeps into the

fissures on the surface of the emeralds. When the fractures contain the oil

they are less eye visible. To complete this process oil is pressurized into

the fissures of the polished stone. This is something that must be accepted;

it's the way it is! The only way you will find an emerald that isn't oiled

is if there are no fractures at the surface of the emerald, so no oil can

get inside the stone. If color is equal, obviously you will pay more for an

emerald if it has no fissures that reach the surface; they simply will have

fewer inclusions. If an emerald that originally had fissures that reached

the surface,is put into an ultrasonic or is steamed clean, then the oil may

be leached out and fractures. This will make the surfacing inclusions appear

whiter and more obvious. In this case, the stone can be re-oiled.

 

Recently, I have read articles that other colored stones such as rubies and

alexandrite have been treated with oils and resins to make surfacing

inclusions less visible. Occasionally colored oils are used on emeralds and

rubies. The idea is to add color while concealing fractures. You want to

avoid buying these because you can't judge the true color or know how bad

the fractures are. This is done to deceive the buyer. Fortunately this is

not common and it is unlikely you will encounter this if you buy from a

reputable source in the United States. Synthetic resins can be used to fill

in fractures in emeralds and other stones with fractures that reach the

surface of the gem. Hardeners are often applied to make the process

permanent.

 

Irradiation

Irradiation means pounding material with subatomic particles or radiation.

Sometimes irradiation is followed by heating to produce a better or new

color for the gem. Blue topaz is the most common example. Although blue

topaz occurs in nature, it is quite rare and pale in color. In the United

States irradiated gems are regulated by the Nuclear Regulatory Agency to in

an attempt to insure there is no harmful residual radiation.

You do not have this protection if you buy it out of this country. Today

irradiation of blue topaz has created shades not found in natural blue

topaz; prices are very reasonable for irradiated blue topaz since there is a

great deal of competition in the wholesale end of this market. If you could

find an untreated blue topaz, it would sell for a price comparable to

untreated Imperial Topaz. Tourmaline can be irradiated to darken pink stones

into red ones; these are indistinguishable from natural red ones. Off

colored diamonds can be irradiated and heated and turned into intense

greens, yellows, blues, browns & pinks. These stones are fairly common..

Irradiated diamonds will sell for much less per carat than the naturally

colored ones of comparable color, clarity grade, and size Cultured pearls

can be irradiated to produce gray or blue colors; but dyeing in these colors

is more common. Irradiated pearls will sell for about the same price as the

dyed pearls, this should be well below the prices asked for pearls with very

fine colors.

 

Dyeing

Without dyeing there would be no black onyx: this is not a natural color of

chalcedony! Chalcedony or more commonly known as agate, is often dyed blue,

green, or orange and carved into bowls, statues, or cut into beads. This is

fine, as there are some lovely pieces around using this stuff, especially

carved animals and the like and no one minds that it's not "natural".

Japanese cultured pearls, which are grown in an Akoya oyster that produces

pearls up to about l0 millimeters, grow into a limited selection of colors

with various overtones of colors. If they are dark gray, bluish, violet,

nearly black, or intense bronze, assume they are dyed.. To meet current

demand for pearls with rose overtones, some cultured pearls have been given

a pink tint; this can be detected by looking for concentrations of dye

around drill holes or around blemishes. On the other hand, South Sea

cultured pearls which are generally larger than the Japanese cultured

pearls, may grow into a variety of exotic colors naturally because they are

grown in a different variety of oyster.

Tahitian black pearls are a good example of naturally colored black pearls.

Cultured pearls with a natural exotic color will command a much higher price

than a dyed one. Dyeing of chalcedony and of pearls is prevalent, permanent,

and acceptable. These colors do not occur in nature; no deception is

involved. Dyeing of other materials, jade, lapis lazuli, turquoise, and

coral, may be less acceptable. Generally, dyeing of these materials is done

to disguise poor quality goods. Dyed lapis lazuli can be easily tested by

rubbing it with a piece of cotton soaked with acetone (fingernail polish

remover). If it is dyed, blue color will eventually rub off on the cotton.

Dyed lapis should be much less expensive than fine natural lapis. In the

case of lapis lazuli or turquoise, the natural material is not that

expensive, so why bother with inferior material unless it is irresistibly

cheap or you just love the color? Dyed lapis lazuli may bleed blue onto the

wearer or his or her clothing (not a fun thing to remove, trust me). Dyed

jade may be tricky to detect, so be careful if the price seems "too good".

An inexpensive tool (around $30) called a Chelsea Filter and supplement

emerald filters can be useful in detecting dyed jade and a worthwhile

purchase if you want to seriously collect natural jade. Coral beads may also

be dyed. Suspect coral that has a very intense color, coupled with an

inexpensive selling price.

Click Here for Information on Jade Treatments

 

Impregnation and stabilization

Impregnation and stabilization are common for turquoise. Impregnation is the

infusion of wax or paraffin into a porous material. Stabilization is the

introduction of a bonding agent, usually plastic, into a porous material. Of

the two processes, stabilization is the most permanent. Impregnated pieces

must be kept away from heat or the wax could melt & leak... not a pretty

sight !!. Some gems are waxed on the surface to enhance luster but this is

not very usual. The upside for stabilized turquoise, is that it will not

absorb oils and discolor as untreated turquoise may.

Opal can be stabilized with plastic to hide crazing, but this is not common

at all and would only be done to deceive the buyer.

 

Bleaching

Bleaching is a process for organic gem materials such as ivory, coral, and

for pearls and cultured pearls. It lightens the color and is permanent and

undetectable. No price difference exists as a result.

 

Coating

Coating is a process rarely utilized where a lacquer or film of some type is

applied to improve a gem's appearance. It is occasionally used on diamonds

to improve the apparent color of an off-colored stone and deceive a buyer.

Opals may have a black coating on the back to intensify the play of color or

to give the appearance of a black opal; this can take the form of a simple

coat of black laquer ot what is called a "doublet." A doublet is a thin

layer of opal cemented to a black onyx base.

Surface diffusion

Surface diffusion is used on sapphires. Chemicals, like berylium, are

infused into the surface at high temperatures. It can improve color or

create asterism (stars). If the surface becomes chipped or abraded, it

cannot be re polished without removing the color.

 

Filling

Filling is used on gems with surface fractures or cavities. Glass, plastic

or other materials are used to fill these holes. This is sometimes done to

rubies. With close examination with magnification you may be able to spot

differences in surface luster, or see a spectral effect in fractures when

viewed with dark-field illumination. The AIGS, The Asian Institute of

Gemological Sciences, has done extensive research on filled rubies.

 

Infilling Diamonds

Diamonds with inclusions are sometimes filled with glass to make them appear

clearer. Yehuda Diamonds have undergone this treatment. Filler can be

damaged by heat, ultrasonic cleaning, and by re-tipping. The filling does

not repair the inclusion, it just makes it less visible.

If you look at a filled diamond closely, rotate it under light, you should

be able to notice a bluish flash. Yehuda will usually refill your diamond

for free if it is ever damaged. Check for guarantees before buying such a

diamond.

 

Lasering

Lasering is sometimes used on diamonds. The process drills very tiny holes

into a diamond to provide access to an inclusion which detracts from the

beauty of the stone. The inclusion can then be, vaporized or bleached to

make it less obvious if it is not burned out by the lasering. Under

magnification laser holes are visible when viewed at the correct angle. A

lasered diamond would be classified in the slightly imperfect or imperfect

category regardless of the improvement in apparent clarity and should be

priced accordingly.

 

Gems that are Not Enhanced

There are some gemstones that are not known to be enhanced. These include:

Garnets, Peridot, Iolite, Spinel, varieties of Chrysoberyl, Catseye

Tourmaline , Malachite, Hematite, and all Feldspar including varieties of

Moonstones. Keep in mind that new technology in gemstone treatment is always

changing and new treatments are appearing.