Enhancement is defined as any processing (other than
fashioning) which improves the appearance or durability of a gem. Determining
whether or not a gem is enhanced is part of the previously discussed
aspects of gemological investigation:
1. Species: What is this gem?
2. Origin: Is it natural or synthetic?
3. Treatment: What enhancements, if any, has it received?
Just to think about: Does it matter if a gem is enhanced?
So what, if a gem is enhanced? If enhancement makes it prettier,
or more durable, what's the big deal, and why do we even need to know?
Here are some of the major issues to consider:
Enhancement can alter the value of a gem up or down. If it makes
an unuseable piece of gem material useable, or an ugly one pretty,
then it has increased the value of that particular piece. On the
other hand, the reality of the marketplace is that "absence
of treatment" in itself, has value. (Why this is so has to
do both with rarity, and with a certain philosophical value many
accord to the unaltered products of "Mother Nature".)
The general feeling among gemologists and ethical gem merchants is
that there is nothing wrong with any type of enhancement, as long
as it is fully disclosed (including care instructions), and the gems
are appropriately priced to reflect their treatment status. Unfortunately,
there are many "ethically challenged" companies and individuals
which seek to profit by doing neither of these.
Two Important Organizations with an Interest in Gem Enhancement
FTC: The Federal Trade Commission regulates many
basic aspects of marketing, advertising and commerce in general. For
gems and jewelry, the pertinent regulations regard certain aspects
of advertising and describing gems, as well as issues of gem weights
AGTA: The American Gem Trade Association is an industry
organization of carefully screened colored gemstone dealers who are
based in the USA. Attaining membership in this organization involves
a lengthy and rigorous vetting process meant to assure that only dealers
who ascribe to the highest standards of ethical business practices
can belong. This organization has had extreme influence, world-wide,
primarily by developing and publicizing standards of ethical business
practices for colored stone dealers, especially as regards disclosure
AGTA guidelines for gem advertising and marketing go well beyond
the generalized and generic ones found in the FTC regulations. Because
more and more countries are adopting the AGTA guidelines and their
coding system, or patterning their own after it, we will be covering
portions of it in this class.
Think of knowledge about gem enhancement to be as a series of positions
on a continuum from 100% known to be enhanced, to 100% known to be
the one end are gems that we know, 100% for sure, are enhanced. This
might be because the treater has presented the material to us as enhanced,
for example: the invoice says "heat treated sapphire" or "dyed
chalcedony". It could also be because in examining the goods we
find incontrovertible evidence of enhancement. For example: microscopic
examination of a diamond reveals the characteristic tunnels made by
lasers for purposes of clarity enhancement, or testing the surface of
a gemstone bead with a swab dipped in acetone removes some of the blue
dye from it.
the opposite end are gems that we know, 100% for sure, are unenhanced.
This category is pretty small actually, as unless you "dig it yourself",
you are taking the word of someone else as to the gem's treatment status.
(Even in this case, it is possible that the enhanced gem rough could
have been "salted" into the natural source!)
all enhancements can be revealed by current testing methods, so in some
cases a thorough (and costly) examination by a trained professional
might only give the equivocal result of: "no evidence of enhancement
found", which is not the precisely the same thing as "unenhanced".
Many low temperature heating processes, and some forms of irradiation
are literally undetectable with today's technology. They leave no tangible
signs distinct from those which might have been the result of natural
these extremes, lies our degree of knowledge of the treatment status
of most gems: three major stopping points on the continuum might be
to be enhanced
- Probably/Possibly enhanced
not to be enhanced
which are assumed to be enhanced are those species in which enhancement
is the standard practice, or those which don't exist, to any extent,
in Nature in the treated color or form . Examples would be blue topaz,
and black onyx which are found in only tiny quantities in Nature, but
produced in huge amounts by irradiation, and dyeing, respectively. This
category would also include oiling of emeralds, a process used on more
than 90% of emeralds in commerce.
which are probably or possibly enhanced are those for which known treatments
exist, but range from being commonly to occasionally used. Examples
would be resin "stabilization" of turquoise, bleaching of
pearls, dyeing of jade, and heating and/or irradiation of beryls , quartzes
and tourmalines. It is in this situation that familiarity with the detectable
signs of enhancement can be most useful. A major goal of this lesson
is to acquaint you with some of the most important of these.
which are assumed not to be enhanced include those for which no treatment
has yet been discovered for the material (or at least none that is cost
effective and non-destructive). This category is highly provisional
as new enhancement processes may be developed or their safety or economics
improved at any time. Examples of gem species which currently can be
assumed to be unenhanced are: spinel, iolite, sunstone and most types
2 general and 12 specific AGTA codes to be familiar with
of Gem Enhancement :-
quest to make gems look better, last longer, or sell at a higher price
is nothing new :
far back as 2000 BCE the Minoans applied thinly beaten gold foil to
the back of transparent stones to make them more reflective.
the treasures buried with "King Tut", circa 1300 BCE, were heat treated
the Elder (23 - 79 CE) in his famous work "Natural History" gives
recipes for oiling and dyeing gems.
early "consumer advocate", Camillus Leonardus, an Italian physician
and scholar, in a work called "Mirror of Stones" published in 1502
gives tips on spotting treated gems, like using a file to test for
hardness, and hefting a gem to determine its specific gravity.
1932 a gemological paper had been published listing fourteen known
as is true today, some of the motives of the gem treaters were honorable,
and some were not.
Major Gem Enhancements :-
The surveys that follow show a few examples (there are many, many, more)
of some of the most common and economically important gem treatment
processes. In some species the treatment is used occasionally, in others
it is common, and in still others it is standard. The organization of
the species presented, within each of these treatment type surveys,
is simply alphabetical, not in order of dollar value, or frequency of
(AGTA Code = H) The most versatile and widely used treatment for gems
is heating. Depending on the gem and the desired effect, temperatures
used vary from those provided by placing the gems in direct intense
sunlight, to near melting point temperatures of 2000 degrees C; periods
of heating range from minutes to several days, and oxygen may be present
or excluded from the heating atmosphere.
The atmosphere in which the gem is "baked" is important, as
it will influence whether its ions gain or lose electrons. That is,
it will determine if a chromophore ion will be changing from Fe3+ Fe2+
or vice versa. A "reducing" atmosphere (one without oxygen)
which can either be supplied via a high tech furnace, or simply by placing
the gems to be treated in a closed container with charcoal), causes
the number to go down (+3 to +2 for example). In an "oxidizing"
atmosphere (oxygen present) the number goes up.
Heating Amber :
Amber is heated for three main purposes: to darken it, to clarify it,
and to deliberately add stress fracture inclusions.
When heated at low temperatures the surface of amber gradually darkens
over time. Much of the clear amber found in nature is a light yellow
to gold color, but shades from tan to gold to orange to dark brown can
be obtained by heating. The color is usually confined to a surface layer
and so is often done after the gems have been fashioned. If desired,
the surface layer can then be partially polished or carved away to provide
contrast or create a design. (Similar low temperature heating of ivory
has been used, by unethical antique dealers, to darken its surface and
create the illusion of great age). Low temperatures must be used on
these gems as due to their organic nature, they will char, melt or burn!
In its natural state, much amber is cloudy or milky, an effect caused
by suspended air bubbles. (If you have ever seen "whipped"
honey, the appearance is very similar). Heating such pieces in oil can
clarify them to a great extent (solid inclusions, if present, will remain
Finally, when amber is heated in oil and then "quenched"(plunged
quickly into a cold liquid), characteristic stress fractures, that look
like flat disks, form. These have been euphemistically called "sun
spangles", and to some tastes, are an attractive enhancement.
The brooch photo below shows clear and cloudy amber of a variety of
colors. The carving illustrates the surface nature of the heated color
(where some of it has been removed by the carving process), and the
close up shows the "sun spangles" in a piece of amber jewelry.
Two species of beryl gems are commonly heat treated. Aquamarine and
Morganite occur naturally in shades of slightly greenish blue, and slightly
yellowish pink, respectively, but the "market preferred" colors
are pure shades of blues and pinks. Heat is used to obtain these preferred
(The temperatures necessary to accomplish the removal of yellow tones
by changing one iron ion to another using a reducing atmosphere, are
low, and therefore, generally leave no obvious signs.) Therefore, aqua
and Morganite of pure blue or pink color should be assumed to have been
heated, unless otherwise stated.
change is subtle and hard to capture with a camera, especially in Morganite
as its color tone is so light, but the images below may give a general
idea of the effect.
Unheated and heated Aquamarines
Unheated and heated Morganites: Morganite images
Heating chalcedony :
Of the many forms of chalcedony, carnelian is the only one which is
likely to be heated.
orangey brown color of carnelian comes from its iron oxide content,
which, when unheated, is hydrated (chemically, it has loosely attached
water molecules bound to it). This form of iron oxide is known as limonite
and is yellow to orange to brown in color. The amount of limonite which
stains the chalecdony will differ, making carnelian naturally highly
variable in tone and hue. Heat removes the bound water from the limonite
and converts it to the unhydrated form, hematite, which, as its name
suggests, is blood red in color.
to the low temperatures involved (the Ancients simply put it in the
sun to bake) it is not possible to discriminate natural heating which
might occur underground during, or after, gem formation, from that which
is man-made. Therefore, if the color is significantly on the red side,
assuming it to be heated, is erring on the side of caution.
Virtually all corundum gems (sapphires and rubies) have been heated.
Many different outcomes from the heating processes are possible depending
on the temperature, atmosphere, and the particular chemistry of the
material being treated.
in corundum, heat : 1) can either increase or decrease color intensity,
2) it can dissolve rutile to clarify a piece, or 3) exsolve it to create
or emphasize chatoyance or asterism. 4) It can be used to partially
heal fractures improving clarity, and 5) it can diminish the tell-tale
appearance of "curved striae" in synthetics by paritally melting
these layers into each other.
learned that heating can remove yellow tones in aqua, but by changing
the conditions, it can emphasize them in sapphire. By using high heat
and an oxidizing atmosphere, a pale yellow sapphire can acquire a deeper,
tones in corundum can be increased or decreased: which way it goes is
controlled by altering heating and atmospheric conditions. High temperature
and rapid cooling under reducing conditions can change the ions of iron
and titanium in pale blue sapphires to a form which results in a stronger
blue color, for example.
the other hand, some corundum suffers from too much blue color like
certain quite purplish rubies and those "midnight" sapphires,
so dark they virtually look black. Some of these gems are susceptible
to conditions (oxidizing at high temperature) which removes some of
the blue, making them much more attractive and saleable.
VARIOUS COLOR ALTERING RESULTS OF HEAT TREATING CORUNDUM GEMS
Blue, therefore correctlng Purple to Red
is also heated to change its clarity status. This is accomplished in
two ways. Rutile is a mineral which, depending on conditions under which
the gem was formed, may be dissolved within the corundum, and therefore
not visible to the eye, or may have crystallized within the corundum
as discrete needles affecting clarity and the chatoyance phenomenon.
"Silky" corundum can be heated and cooled under precise conditions
which will cause the rutile needles to dissolve into the corundum thereby
greatly clarifying the gem; or conversely, gems with significant dissolved
rutile can be subjected to heat and temperature regimes which encourage
the dissolved rutile to "exsolve" into solid needles.
Due to the possibility of clarification, an increased percentage of
potentially chatoyant corundum is now sold as transparent material,
and the number of available star gems has decreased.
with significant fracturing that causes loss of transparency can be
subjected to very high heat which, by melting the thin edges of the
fractures causes partial healing and, therefore, clarification to occur.
A ruby whose originally modest star potential was enhanced by
A pair of once silky Blue Sapphires, clarified by heating
for heating in sapphires includes discoid stress fractures, singed (partially
melted) surface facets, internal crystals with rounded, melted edges,
and partially reabsorbed silk.
against heating is shown by intact silk, highly angular included crystals,
and lack of discoid fractures.
Discoid fracture in Sapphire
Proof of no high temperature heating
corundum gems cannot be called either way, so it is prudent to assume
heating, as it is so prevalent in the marketplace.
After diamonds have first been irradiated to green and blue green, they
are often heated (a process termed "annealing") to further
alter their color. Generally, such stones change to yellow or brown,
but, rarely, some pieces with slightly different chemistry or crystallography,
heat to highly desirable pink, purple or red colors.
brown diamonds shown below are examples of annealed stones. The second
photo shows an irradiated blue stone before and after annealing. The
annealing takes place at relatively low temperatures (well within the
range of that produced by a jeweler's torch).
cases of annealing have taken place when jewelers neglected to remove
irradiated blue or green diamonds from their settings before repairs
were made customers were not happy to find their diamonds had turned
yellow or brown.
Diamonds that have been irradiated then heated to change their
color, the brown stones were deliberately changed
The yellow one was an accident
New Process to be Aware of :
new high pressure/high temperature process for color enhancing diamonds
is beginning to impact the market. It uses the same equipment and conditions
that are have long been used to synthesize diamonds, but the treatment
time is far shorter than that used for synthesis. AGTA (Code = HP).
HPHT for short, it can produce colorless, pink, and blue gems from some
types of off-color rough or cut stones. Due to the very high temperatures
used, only high clarity stones can be treated.
all diamonds react to this treatment, but when they do the results are
stunning and the value of the stone jumps significantly. About 5% of
diamonds can be made colorless, and a larger percentage can be made
into "fancies". The fancy colors, are more subdued and natural-looking
than those produced by irradiation, and unlike the case with irradiated
stones, there are no obvious signs to help identify them as enhanced,
so laboratory analysis is required.
HPHT "Press" used by Sundance, Inc. to color treat Diamonds
An example of a "before and after" showing a dramatic
improvement in color
Sundance, Inc. is doing business honestly, and attempting to prevent
fraudulent representation of its goods, you can see, I think, how tempted
some might be to try to pass off these relatively inexpensive enhanced
gems as the higher priced "real thing".
As with corundum, heating quartz can have various effects. Gentle heating
of dark or muddy amethyst lightens the purple, and can reduce unattractive
grey and smokey tones. At higher temperatures amethyst converts to yellow
or orange citrine or, rarely, to yellow-green prasiolite. (Chemical
or physical factors present in amethyst mined in only a few sites are
of the sort that create prasiolite when heated, so it is much rarer
than citrine. Citrine does occur naturally, in which case Nature has
already supplied the heat, but in general, natural color stones are
notably lighter in tone than those produced with human help.
quartz when heated can turn yellow, also making citrine although this
is less commonly done than heating amethyst. Tiger'seye which is usually
a golden yellow color will become red upon heating.
OUTCOME OF HEATING AMETHYST
Citrine from heated Smokey Quartz
Enhanced Red Tiger's Eye
Two types of topaz are routinely heated. 1) White topaz, as a first
step in its color enhancement, is irradiated to brown, and it must then
be heated to create a stable blue color. 2) Much natural ("precious")
topaz of a yellow or orange color, some with subtle pink overtones,
is unattractively muddied with brown, which can usually be removed or
reduced by heating, a process traditionally referred to as "pinking".
As can be seen in the photo of the four stones on the right below, the
results are variable.
processes use relatively low temperatures, so there is little evidence
left behind. Once again, it is prudent to assume that any blue or precious
topaz has been heated unless it can be proven otherwise. Natural blue
topaz is very rare, and when found it is generally quite pale, and pinking
of precious topaz rough is standard practice virtually everywhere that
it is mined.
Heated (sky, Swiss and London blue topazes) blues are heated post-irradiation
Pinked precious Topaz
Heating can be useful in lightening the color of some dark blue and
green tourmalines that without such treatment, look almost black. Unfortunately,
not all dark stones respond to the heating. In some cases, as with amethyst,
muddy tones also can be lightened or removed. For these reasons, the
majority of blue and green tourmaline rough is heated, so it is prudent
to assume it. Some red tourmalines (rubellites) can be improved in color
by heating, and though not common practice, it is occasionally done.
As with topaz, the temperature used
for tourmaline is fairly low, so there are few telltale heat-altered
inclusions to leave evidence of it. Such stones, however, can be more
brittle than unheated ones which can sometimes be deduced by noticing
facet junctions that are abraded more easily than the norm.
Zircon which occurs naturally in orangey brown shades, has both a long
history of use as a gem, and a long and creative history of enhancement
same stones are sometimes put through a series of heat/atmospheric enhancement
regimens in an attempt to induce a change to a more desirable color
such as blue, blue-green, red, yellow, orange, or red. Individual stones
(based on their own unique chemistry) react in various ways. The description
that follows applies to the majority of zircon gems:
the first step of treatment, rough zircon is exposed to temperatures
of around 1000 degrees C, in a reducing atmosphere where many brown
stones turn blue, some turn white and others don't change.
1st Round : before, brown, and after : blue or white
which do not respond may then be re-treated at slightly lower temperatures
of about 900 degrees C, in an oxidizing environment. Results can vary
from yellow to white to red.
2nd Round : before : brown stones which didn't respond to initial
heating, after : yellow, white, or rarely, red
may sometimes go through several cycles of heating, and can get rather
brittle, which may make facet edges susceptible to abrasion.
Although shades of orange, red and yellow
are occasionally found in Nature, white and blue occur so rarely that
heating must be assumed for these colors.
Heating Zoisite :
When a transparent variety of zoisite was first found in Tanzania, Africa,
there was little excitement due to its dull, brownish yellow color.
Experiments with heating, though, soon yielded gems of a beautiful blue-violet
color. As it turns out, heating was turning one of the color axes of
this naturally trichroic gem from yellow-green to colorless, and allowing
the less dominant blue and violet colors to be clearly seen. "Tanzanite"
was born. As is so commonly true of gem rough, some individual pieces
have atypical chemistry or crystallography, and react differently to
treatment than most. In the case of this type of zoisite a very small
percentage of the gems heat to an attractive green to blue green color.
Dubbed "Green Tanzanite" (a misnomer, but one that stuck),
such specimens have high value as collector stones, and are quite beautiful
in their own right.
Typical unheated color of Tanzanian zoisite, the usual blue-violet
result of heating, the rare green result
you want your gems unheated :
There are two major groups of gems that aren't heated: 1) heat sensitive
gems like opal, apatite, pearls, and turquoise, and 2) those for which
heating makes no improvement, or isn't economical such as garnet, spinel,
chrysoberyl, iolite, peridot, sunstone, moonstone, jade, and most collector
stones. If unheated is what you want, that is fine, but outside of the
groups listed, you can expect to pay a premium for unheated goods, and
some types of gems like blue zircon and Tanzanite will be off limits
Another point to keep in mind is that "unheated" doesn't mean
the same thing as "unenhanced", although there are those who
can profit from implying it does!
I have seen several dealers on independent websites, online auctions,
and at gem shows that proudly advertise their wares as "unheated"
when their goods have been, dyed, coated, irradiated, oiled or in some
other way enhanced. Naive buyers can be deluded into thinking they've
purchased an unenhanced stone.
(AGTA Code = R) After heating, the most commonly used treatment for
gem enhancement is irradiation. With some important exceptions (like
diamonds), treated stones are usually not distinguishable from untreated
ones, as gems are often subject to similar, but natural, irradiaton
effects during, and after, their formation.
variety of sources of, and processes for, irradiation have been tried,
some, proving unsatisfactory, have been abandoned, others are still
in use. The earliest experiments with irradiating gems used alpha particles
(helium nucleii) which worked as desired, but left the gems with strong
and highly persistent residual radiation. Today, beta particles (electrons)
generated in linear accelerators, neutrons from nuclear reactors, and
gamma rays usually from radioactive cobalt sources are used.
the bombardment with neutrons and, to a greater extent, with electrons,
can leave some residual radioactivity, its duration is relatively short.
Government agencies in the USA, and other gem irradiating nations, have
strict regulations for the holding and testing of irradiated gems to
assure that they are not released to the public until they are safe
to handle and wear.
we saw to be the case with heating, different types and durations of
irradiation produce different results. Combining this fact with the
idea of individual variation in gem chemistry, and that irradiation
may or may not be followed by some sort of heating process, and we can
begin to appreciate the tremendous diversity of possible results.
Irradiating beryl: Colorless beryl (variety = Goshenite) can be irradiated
to stable shades of yellow to gold (variety = golden beryl or heliodor).
Unenhanced golden beryl is also common, and it is essentially impossible,
outside of a large gemological laboratory, to tell whether it was man
or Nature that supplied the color producing irradiation.
boondoggle perpetrated on the gem buying public several decades ago,
is still remembered by some wary dealers and buyers. Some beryls, with
an unusual chemistry, turned a vivid and attractive blue when irradiated.
They were rushed into the market with much fanfare under the tradename
"Maxixe" beryls. The fly in the ointment was that these stones
were unstable in light, and reverted to their intially colorless state
relatively quickly under normal use conditions.
There would be little point in bringing up this unsavory memory, except
that in 2003 explorers in Canada unearthed a bright blue deposit of
beryl reminiscent of the Maxixe color. This material is colored by iron
(not irradiation), and the color is stable. As of yet, the mining efforts
have not yielded any facet quality rough, but exploration is proceeding.
The only known deposit is presently owned by "True North Gems"
and their material, already popular with collectors, has been christened
Unstable irradiated "Maxixe" Beryl, natural color, stable
True Blue Beryl
As presented in the section on heating gems, diamonds irradiate to green
or blue green. Another color which is commonly produced via irradiation
is "black". Well, actually, it is not black but a very, very,
dark green, and the visual impression is definitely black.
do occur naturally in black (if they are highly included), but irradiated
"black" diamonds, when subjected to very concentrated light
source, like a fiber optic light, show green color at the extreme edges
where the girdle or facets are thinnest, whereas this is not true of
unenhanced black diamonds. Virtually all the black diamonds used in
jewerly today are the irradiated type.
Typical blue-green color of many irradiated Diamonds
Very dark green "black" irradiated rose cut Diamond
You will recall that these irradiated
stones can then be annealed (heated) to brown, yellow or, less often,
some of the rarer fancy colors like red. These heated and/or irradiated
colored diamonds tend to have more vivid (some might even say "garish")
colors than naturally colored fancies.
Unlike what is seen with the majority
of species which are irradiated, the process does tend to leave tell-tale
signs in most diamonds. Patterns of color zoning that show up microscopically,
with certain lighting conditions, can usually give the trained observer
evidence of the treatment.
enhanced blue colored diamonds, though, there is a definitive test electroconductivity.
Diamonds that come by their blue color naturally contain boron impurities
which allow them to conduct electricity, irradiated blues get their
color by the effect of irradiation on their crystal structure, and like
all other diamonds, don't conduct.
One of the many possible enhancement processes that are used to change
color in cultured pearls, the use of gamma irradiation has different
effects on fresh and saltwater cultured pearls.
When saltwater pearls, like Akoyas,
are irradiated, it turns the bead nucleus (made of shell) dark, which
then shows through the unaffected translucent nacre layer making the
pearl look grey or perhaps grey-blue. In the case of cultured freshwater
pearls, the irradiation actually affects the nacre layers creating silver,
gold, black and even multi-hued, often intensely metallic looking colors.
(This difference is due to the slightly different trace element chemistry
of nacre produced in fresh vs saltwater.)
treatment in both cases is stable. With saltwater pearls it is usually
possible to get a magnified view down a drill hole which will reveal
the darkened bead nucleus. Identifying irradiated freshwater cultured
pearls (which usually have no bead nucleus) can be as simple as becoming
familiar with the natural color range of these gems. Once that is accomplished,
the completely unnatural looking irradiated stones jump out at you and
Irradiated freshwater Cultured Pearls
Irradiating Quartz :
Colorless quartz, rock crystal, is irradiated to produce smokey quartz
in shades from light to very dark brown or grey-brown. The smokey quartz
found before modern irradiation techniques were developed, and a proportion
of that mined and sold today, comes pre-irradiated by Mother Nature.
A relatively recent discovery of a unique
type of rock crystal at a particular series of mines in Brazil gives
quite different results when irradiated. The resulting material known
variously as "neon" "lemon" and "oro verde"
quartz has a highly saturated, slightly greenish yellow color. Due to
its striking color and its availability in inexpensive, large, clean
pieces, it has become the recent darling of carvers, concave facetors
and fantasy cutters, as well as a staple of the home shopping channels,
and internet gem auctions.
Once again, with smokey quartz, we have
a case where it is difficult to impossible to determine the origin of
its color, and it is best to assume it has been irradiated by man, in
the absence of proof to the contrary. Not so, with the yellow material,
as its only known source is from the irradiator's factory.
Irradiating scapolite and spodumene
Although these two gem species are likely to be unfamiliar outside of
gem circles, they provide some interesting examples of the effects of
irradiation. Scapolite is found naturally in light to medium shades
of yellow, and also in pale lavender. The yellow material can be irradiated
to a much deeper, and more brownish, shade of lavender than that which
Spodumene occurs naturally in colorless,
light to medium pink/lavender (Kunzite), and very rarely in a chromium
colored, grass to emerald green stable variety known as Hiddenite. Kunzite
can be irradiated to a light to medium green color which is often given
the misnomer of Hiddenite, and sold for inflated prices to naive collectors.
Not only is the irradiated material not Hiddenite, as its color does
not come from chromium, but it fades quite noticeably in the light,
a fact too rarely included in the sales pitch.
Irradiated Purple Scapolite
The world's supply of attractively colored pink to red tourmaline has
recently been greatly increased by new discoveries. Some Brazilian tourmalines,
formerly rejected due to poor color, and the majority of the large new
deposits being found in Africa, are irradiated to diminish brownish
tones. The permanent improvement in appearance (alas, not all pieces
are susceptible) is similar to that displayed in the two stones below:
Typical "before and after" colors of some low grade
tourmaline that is susceptible to drastic improvement in color
In terms of sheer carat weight, and probably also in terms of economic
value, blue topaz is the most important irradiated gem. Colorless topaz
is plentiful and inexpensive, but not all of it will irradiate successfully.
Treaters generally screen the rough with an inexpensive gamma ray treatment
which identifies the rough which will benefit from further irradiation,
before proceeding with more costly and time consuming treatments.
"good candidates" then go to either a linear accelerator to
be bombarded with electrons, or to a nuclear reactor to be exposed to
neutrons. Depending on the duration and type of irradiation, and the
sort of heating process used afterward, the results vary from sky, to
Swiss to London blue. Other slight color variations have been produced
and given their own tradenames like "electric blue" and "neon
blue is the scarcest and most expensive type because it requires neutron
exposure (most expensive process), and the longest holding times. Now
that so many other types of gem materials are being irradiated, topaz
treaters are having to pay more to "book" accelerator or reactor
time, and prices for these once quiet inexpensive gems have correspondingly
most gem materials, much, if not most, of the cost of the finished gem,
is associated with the gem rough itself. Blue topaz is an interesting
exception to this, as the rough is the least expensive part, with fashioning,
and even more so, treatment, responsible for the bulk of the costs.
irradiated colors are stable, and the gems are perfectly safe to wear,
but the dual heat/irradiation processing does leave them somewhat more
brittle than unirradiated stones. Added to the natural tendency for
cleavage, this makes blue topaz one of those gems which, despite its
hardness of 8, is not a good choice for daily wear rings or bracelets.
/ HEATED TOPAZES
Unenhanced White Topaz
introduction of huge amounts of blue topaz into the market place in
the last several decades has had some interesting side effects on other
1. For a time, it depressed the prices of aquamarine, as sky blue topaz
made a pretty good aqua simulant at about 1/10th the price. With time,
though, most aquamarine lovers went back to their original gem choice,
with the ironic twist of a noticeable decrease in the traditional preference
for heated "pure blue" stones. More and more aqua fanciers
are now seeking out the greenish blue unheated stones possibly because
these are less likely to be mistaken for the ubiquitous and inexpensive
2. The other effect has been to literally wipe out the identification
of the word topaz with the color yellow. Yellow, or precious topaz,
was, until the advent of irradiated blue, the most common and familiar
type, and is still the traditional birthstone for the month of November.
For centuries, these were the colors that the word "topaz"
(AGTA Code = W) When the surface of a gem is coated with colorless wax,
(or oil) the process is termed waxing. Generally, this treatment is
used with stones with a vulnerable, porous surface, or those with microscopic
surface imperfections whose polish luster can be boosted with it. Porous
materials like turquoise that have been waxed, are thereby, at least
partially, protected from absorbing skin oils and other environmental
Although, not permanent, the gem community
tends to adopt an extremely forgiving attitude toward this treatment,
as it is both a very long standing tradition, and a simple matter to
re-wax the gem. (Paraffin and beeswax are the traditional materials
used, and re-doing a gem can be as simple as painting on melted wax
and buffing off the excess).
Most of the world's highest grades of
turquoise and jadeite can be assumed to have been given this treatment.
It is also occasionally used with lapis lazuli, rhodocrosite, serpentine,
variscite and Amazonite.
(AGTA Code = D) Dyeing is relatively easily accomplished with porous
gems and those crystalline gems which are aggregates. The pores and
the spaces between the microcrystals allow the dye to be taken up. Single
crystal gems, however, are not good candidates for dyeing as they will
only take up dye where they have surface reaching fractures.
is really only one case in which dyeing is an "accepted industry
standard", and has no effect on the value of the gem: black onyx.
All other instances of dyeing (when disclosed) negatively affect the
value of the gem, in some cases, dramatically.
of porous and aggregate gems which are frequently dyed are chalcedony,
jade, coral, pearls, and howlite.
are some cases where the absorption spectrum of a gem can identify specimens
which are dyed, but they are rare. The usual ways of detecting dyed
1. By microscopic examination: looking at pores, bead drill holes, and
surface fractures for dye accumulations.
2. Testing with a solvent, a destructive test, yes, but one which can
usually be done in an inconspicuous area. Useful solvents are acetone
and denatured alcohol, but not all dyes are soluble in them, so a negative
test in not conclusive.
3. Comparison to the normal range of gem colors and evaluation of the
avialability and cost --> naturally colored chalcedony in unknown
in hot pink for example, and Nature doesn't yield neon green pearls.
Saturated, medium dark, lavender natural color jade is worth a King's
ransom, so pieces of that color seen on ebay for $10 are very likely
to be dyed. (Compare the color of the inexpensive jade beads below with
the picture of the very expensive natural color lavender jade ring above).
Dyed Coral beads
Dyed freshwater Cultured Pearls
Typical natural color of Chalcedony
Typical non-natural color achieved by dyeing
of the most commonly dyed materials in today's marketplace is howlite,
an inexpensive, porous, white mineral that generally has grey to black
veining. It has been used to simulate turquoise, lapis, rhodonite, and
other opaque gems. The dye penetrates only a short distance into the
gem, so scratches and chips are revealing, but when undisturbed, a piece
can be quite convincing.
Howlite in its natural color
Dyed to imitate Lapis Lazuli
Dyed to imitate a turquoise nugget, the nugget sawn apart to reveal
the undyed interior
single crystal gems are dyed, they must be fractured first. In order
to achieve this, the age old method is "quench crackling".
Generally this is done by heating the gem, and plunging it in cold water,
but strong ultrasonic vibrations have been used to accomplish the same
thing. Dye can then be absorbed into the fractures which, when numerous
enough, give the piece an overall color.
Two pieces of quench crackled, dyed rock crystal quartz
The pink one has been magnified and shows clearly that the dye
is only in the fractures
In the great majority of cases, the dye is a chemical or pigment of
either natural or synthetic origin. An example is the use of silver
nitrate, a chemical that darkens on exposure to light, which has been
used on pearls for many years.
are a couple interesting cases, however, which involve "carbonization".
Chief among these is the production of "black onyx". Here's
one of those cases where a misnomer continues in use, just because of
familiarity and convenience. (Onyx by definition is has color bands,
so a solid black material just doesn't qualify). There are very small
amounts of black chalcedony found in Nature, but the virtually all of
that in commerce is carbonized chalcedony.
to light grey chalcedony is soaked in a sugar solution until its internal
pores are filled with it, then it is boiled in sulfuric acid which "carbonizes"
the sugar turning it black. There are now microscopic sized black specks
throughout the piece, giving it a uniform and stable black color. When
I was first learning about gems, I just couldn't believe that this primitive
method, developed hundreds of years ago, was still the major mode of
production but it is.
"Black onyx" ring, technically "carbonized chalcedony"
similar process is used to color certain matrix opals (particularly
those from Australia's Andamooka region), whose matrix is a light color,
giving little contrast to the patches of color of the opal within the
matrix. The result of the darkening of the matrix is an improvement
in contrast and therefore in the appearance of the color play.
(AGTA Code = B) Probably the most routinely bleached gem, is pearl.
Historically, long before cultured pearls were invented in the early
20th century, pearl fisherman would spread their treasures out in the
bright sunshine, carefully rotating them over a period of time, which
tended to lighten and even the color, and diminish some unsightly dark
spots. Light is still used in some pearl processing facilities. (Anyone
whose hair gets lighter in with long exposure to sunshine, or whose
window drapes have faded over time, will realize how effective a bleach
light can be.
its use in removing blemishes and evening out color, bleaching is a
tremendous aid to manufacturers in matching pearl colors. Today's pearl
consumer demands that each and every pearl in a strand, is exactly the
same shade. Mother Nature prefers to make a wide variety of shades,
even within the same species of oyster or mussel, living in the same
body of water.
In addition to light, chemicals such
as hydrogen peroxide (Lady Clairol, anyone?) and chlorine (as in Clorox
bleach), speed up the process, but on delicate organic gems like pearl
and coral, must be used at low strength and with care.
Large scale bleaching of pearls with chemicals and/or under lights
coral is rare and valuable, so is black coral. Depending on the ups
and downs of the market, the vagaries of supply, and prevailing public
tastes, there are times when black coral is bleached to gold (peroxide
Bleached Black Coral beads
is another frequently "bleached" gem, but in this case strong
acids are used which really aren't bleaching the color to a lighter
shade, they are literally dissolving away discoloring inclusions. Such
bleached jade requires further treatment to seal the cavities formed
by bleaching. (See below.)
Acid bleaching is also used in conjunction
with laser drilling in diamonds to remove "carbon" spots and
other discolorations. The laser creates a narrow channel by which the
acid can penetrate the interior of the diamond and do its work. As with
jade, this process is generally followed by one which "fills"
the cavity. (Again, see below)
(aka "stabilization") : (AGTA Code = I) :-
a colorless, hardened, resin is suffused throughout a porous stone to
make it more durable or improve its appearance, it has been impregnated.
A common market term for such gems is "stabilized". There
is only one imporant type of gem for which this treatment is essential
without impregnation, ammolite is too fragile to withstand fashioning
or wear. Unenhanced specimens, exist, but are suitable only for display.
Other gems like jade or turquoise are
commonly treated in this manner. Low grades of highly porous turquoise
that may have nice color, but are excessively fragile, or near impossible
to polish, can be greatly improved by resin impregnation. "B"
and "C" jades, after being acid bleached have resin infused
into the resulting cavities (if the resin is colored, then the piece
is considered dyed, "C" jade).
(AGTA Code = O) and Filling :-
(AGTA Code = F) Both of these types of treatments involve the filling
of surface reaching fractures or cavities with colorless oils, resins,
or glass. They are done for the same reason: to clarify a gem, by decreasing
the relief of the fracture or cavity. The difference between them hinges
on whether the filling material is essentially a liquid (oil or unhardened
resin) or solid (hardened resin or glass).
Of the two, oiled gems are more accepted
in the gem marketplace and do not depress value greatly. Even though
the oil treatment is temporary, the favorable viewpoint comes both from
the long standing and widespread use of gem oils, and the fact that
it can be successfully be re-done if necessary. Virtually all emeralds
are oiled, some as rough at the mine site, others only after they are
cut. Certified unoiled emeralds bring a 10% - 20% price premium. If
the oil is colored, then the emerald is considered to be dyed, and its
price is much more severely affected.
Emeralds : Routinely oiled to improve clarity
gems are another matter. Although it can be argued that the filling,
being hardened, is less likely to evaporate or be dislodged by cleaning
and wear, several factors create a generally negative impression that
translates to a drastic effect on gem prices.
The solid resins can discolor and become
more opaque with age, and since they cannot be removed, will then permanently
degrade the gem's appearance. Fairly large areas can be filled with
solids, which are less durable than the host gem and can become scratched,
chipped or dulled with wear. This process is primarily used with rubies
and diamonds, both very valuable gems, so it must not be forgotten that
these chunks of glass or plastic resin are adding weight to the gem.
That is, adding weight of a material which is not valuable, but which
the customer is paying for.
Until just recently, diamonds were the
only major gem for which glass filling was a concern. Now, however,
the number of glass filled rubies in the marketplace has risen to the
point where gem professionals and alert buyers need be wary. Glass or
plastic filled gems are worth only a small fraction of the value of
their unenhanced equivalents.
Fortunately, there are several ways
to detect glass or plastic areas in gems. Under reflected light, the
luster difference between a ruby or diamond, and its glass filler are
easy for the trained observer to spot. Some fillers fluoresce and give
themselves away. For those which are confined to thin fractures, the
"flash effect" is a tell-tale sign.
Flash Effect :-
As a gem is rocked and tilted under
appropriate lighting and magnification, these thin filled areas will
first flash one solid color like orange and then, at a different angle,
a different color like purple. Novices may confuse this with the cleavage
rainbow seen in unfilled fractures, but in the flash effect, only one
color is seen at a time.
Fracture filled Diamonds showing the "flash effect"
which are properly disclosed as oiled or filled, should include appropriate
care instructions. For example, oiled emeralds should not be steam or
ultrasonically cleaned. Jewelry containing filled rubies and diamonds
should not be repaired or resized without removing the gems from the
settings, as heat from a torch or immersion in metal cleaning solutions
can cause melting or etching of the filler.
Laser drilling :-
(AGTA Code = L) Thus far, this treatment, a type of clarity enhancement,
has been seen only in diamonds, and is virtually always combined with
acid "bleaching" and fracture filling. The purpose of the
tunnel created by the laser is to provide a channel for the acid and
glass, or resin, to enter. The entry points are tiny, as seen in first
photo (red arrows) and can be easily overlooked, but microscopic examination
(usually 10x is sufficient) makes this treatment one that can be positively
Laser drilled diamond, surface view and magnified view
Laser drilled Diamond, note flash effect being shown by filled
fracture at the base of the laser tunnel
(AGTA Code = U) When gems are diffused, they are heated to very high
temperatures, just to the verge of their melting points. This heating
is done in the presence of a material which contains chromophores such
as titanium, chromium or other atoms, which are then able to diffuse
into the stone's surface or interior to change color or create phenomena.
Two such processes are currently in use: 1. Surface diffusion, and 2.
Bulk or "lattice" diffusion.
Surface diffusion has been around for decades and, until recently, was
pretty much confined to use on blue sapphires and the occasional ruby.
By packing already faceted, light colored stones into a container with
powdered titanium and iron, and heating to very high temperatures, a
thin surface layer rich in these chromophore elements is formed, which
through selective absorption, greatly darkened the apparent blue color.
Such stones must always be repolished afterward as the high heat tends
to mar the surface. In the repolishing process it is inevitable that
some of the thin layer is unevenly removed, so that when viewed under
immersion and/or in diffused light, an uneven pattern of color-->
paler on some facets than others and darkest at the edges of the facets,
can be seen.
If the diffused stone has inclusions at all, these will also show the
typical signs of high heat, such as partially resorption of silk, partial
melting of crystals, or stress fractures. With such obvious signs of
treatment, only the unschooled or unwary buyer is likely to be duped.
Below is a picture of a 1.53 ct. sapphire. A beautiful stone: top color,
eyeclean, and reasonably well cut. In today's market one might expect
to pay between $1000 and $1500 per carat, retail, or even more in an
upscale jewelry store for a sapphire with this kind of appearance. This
stone's actual retail price was $150 for the piece, or less than $100
per carat. What a bargain, you say --> and why so cheap? (No, it
is not a synthetic!)
An attractive, color enhanced, natural Sapphire
price paid, was, however, appropriate to the stone. It is a natural
origin sapphire, but it is has been color enhanced by surface diffusion.
The lovely color layer has a thickness of much less than one millimeter,
the rest of the stone is either colorless or an unappealing pale blue
stones represent a bargain, as long as the customer understands the
limitations inherent to them. Any scratch, chip or nick will remove
the color layer revealing a light spot, and the stone cannot be recut
or it would lose its color entirely. As a stone to be used in a pendant
or earrings or even a ring worn once in a while, it will look beautiful
for many years, but it is not an appropriate choice for a frequently
worn ring or bracelet.
can see from the photo, that looking at the stone in ordinary light
doesn't tell you the source of its color. Below are two 10x magnified
photos of this same gem, (you can do this kind of observation with your
loupe, no fancy microscope is necessary).
the first, the gem is seen in diffused light, in the second, it is immersed
in water and viewed with diffused light. Both photos give unequivocal
evidence of surface diffusion. Look closely and note the color differences
from facet to facet (natural color zoning does not follow facet shapes),
especially telling is the way the color is darker along the keel and
at many of the facet boundaries.
Magnified views of a surface diffused blue Sapphire
diffused light, under immersion in water with diffused light
Making Stars :-
When titanium dioxide (rutile) is surface
diffused into a sapphire, and the heating and cooling is controlled
so that it exsolves into needles, asterism is created in the stone.
Again, you are looking, in the photo below, at a natural sapphire, but
one that has been surface diffused with rutile. Such gems are very inexpensive
compared to unenhanced, natural star sapphires. In comparison to an
unenhanced star stone, the star figure is stronger, more even, and seems
less mobile as the light source shifts direction.
A surface diffused Star Sapphire
recent entry into the world of surface diffused gems is topaz, now available
in bright colors such as green and red as well as bi-colors. The advertisement
below is from an ethical company (RioGrande), which is one of the major
suppliers of gems to jewelers: notice the enhancement code (U) and the
appropriate warning about recutting.
In 2004 Leslie and Company introduced the first surface diffused bi-colored
topazes to complement their existing line of tradenamed diffused topaz
Surface diffused Topazes
Bulk or lattice diffusion was discovered to be occuring in 2003 when
stones that began appearing the market in 2002 were critically examined.
The gems were sapphires of an extremely rare and valuable color called
"padparashah" (orangey pink). The inexplicably large numbers
of fine colored stones suddenly available, raised questions that led
to a fervor of activity among the staff gemologists in organizations
such as AGTA and GIA.
Athough the treaters were freely acknowledging that the gems had been
heated, they insisted that that was the end of the story. Adding to
the confusion, the stones did not fit the profile of diffused gems as
the color penetrated well into the interior in many causes completely
throughout the stone.
Suffice it to say that they were finally demonstrated to be the result
of a new diffusion process using the light element beryllium (Atomic
number = 4) as colorant. With its small atoms, the beryllium chromophore
was able to diffuse much further into the heated stones than titanium
or chromium with their much larger atoms. The source stones were primarily
light pink African sapphires which were then being were treated in Thailand.
Bulk diffused "padparashah" Sapphires
The "pre-discovery" prices
were extremely reasonable for naturally colored, or simple heat treated
paparashahs, but outrageously inflated for diffused goods. In the interim
between the time the stones were stealthily introduced into the market,
and the time their true nature was understood, quite a few greedy collectors
and dealers re-learned the old lesson "If it seems too good to
be true, it probably is".
Viewed under diffused light and /or
immersion, most of these gems show normal color patterns. Although they
do have inclusions typical of high heat, positive identification of
a particular gem as being beryllium diffused, requires the services
of a large gemological laboratory.
Although they are considerably more
durable than surface diffused stones, recutting could still be a risky
proposition, especially on larger stones.
(AGTA Code = C) Coated gems are those that have been treated with surface
enhancements such as laquering, inking, painting, foiling, or sputtering
of a film to enhance color, improve appearance or add phenomena.
Coating has a long history: from use
of gold foils in antiquity, to the painted back Rhinestones of the 19th
century, to today's iridescent metallic coatings. Coatings are usually
fairly easy to detect, but can escape notice if they are applied only
to back of the gem (as in a "foilback") and the gem's setting
is fully closed. The coatings of foilbacks range from crude and obvious,
to sophisticated and well hidden, as seen below.
Contemporary "gumball machine" quality foilback ring
(glass with metallic paint)
1910 high quality Rhinestone brooch (glass with metallic paint)
Perhaps the most nefarious of the fraudulent
uses of coating is an old (but still in use) trick of putting a tiny
drop of indelible blue ink or paint underneath the prongs holding an
off-color diamond in its setting. The prong hides this dot of color
from all but the most experienced eyes. The effect of the light reflecting
off those blue areas and mixing with the generally yellowish light emerging
from the gem, makes the yellowish stone appear shades whiter. (As an
example, this technique might raise a stone's apparent color grade from
M to F allowing the seller to make an undeserved profit.)
The most common coatings in today's
gem market are the metallic vapor films that create iridescent gems.
Metallic vapor coated iridescent quartz ("aqua aura")
view of metallic vapor coated "mystic topaz"
of Enhanced Gems :-
are no overall rules, as some enhancements increase durability, while
others decrease it. But these general precautions will protect almost
any enhanced gem: avoidance of solvents, ultrasonic and steam cleaning,
gentle wear, protective settings, avoidance of recutting, and removal
of gems from their settings prior to jewelry repair.