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". New treatments involving
bleaching and polymer impregnation have replaced the simple dying
that jade underwent for decades. An inexpensive tool (around $30)
called a Chelsea Filter and supplement emerald filters can be
useful in detecting simple dyed jade but are not reliable in detecting
ploymer impregnation. 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.
Disclosure
With
some gemstones enhanced by specifically defined treatments according
to the guidelines of the CIBJO, it is a requirement of the Trade
in the US to make such disclosures and in any case a vendor should
always disclose any known treatments or enhancements (remember,
they may not always know themselves, with imported Gems) and record
it on your bill of sale. Most vendors are very honest and forthcoming,
but it is YOUR RESPONSIBILITY TO ASK.
Caveat Emptor !!!
