Synthetics are man-made gem products. The Federal Trade Commission
is quite specific in forbidding the use of the term "gem"
or "gemstone" (or any recognized species or variety thereof),
unless that product is solely and exclusively the work of Nature.
All other products offered for sale must be clearly identified with
a readily understood adjective that indicates their synthetic status.
Acceptable terminology for synthetics is variable, but would include
product labels similar to the following: "synthetic gemstone",
"laboratory-grown ruby", "cultured pearl", "created
emerald", "man-made sapphire", "reconstituted
Synthetics can be exact copies of natural gems, or they can be unique
materials which are not found in Nature.
1. Examples of the former include the synthetic rubies and emeralds.
Such creations have virtually the same optical, chemical and physical
properties as their natural counterparts.
the most common example is pearls. These gems, which are already in
beautiful shapes as found, are occasionally put into their mountings
without even drilling a hole in them.
metalsmiths mount an unfashioned gem, strategically placed prongs, or
special adhesives are used to make attractive and secure settings. The
pictures below show some of the ways in which unfashioned gems are used:
Chatham brand, emerald crystal cluster set as a pendant
(Also placed in this category are those created materials which are
accurate copies of natural gems, except that they are produced in colors
not found in Nature. Examples would be blue quartz, and white spinel
except for color, these give all the same test results as the natural
versions of that gem.)
a popular synthetic widely used in industry and as a gem, can
be made in a variety of colors from white to pink to green,
and has no analog in Nature
and fakes, synthetic gems are a relatively modern development. Although
there were some successful laboratory experiments earlier, the economically
viable commercial production of a synthetic gemstone began with synthetic
ruby produced in France in 1902 by Auguste Verneuil. By 1907 production
was 5 million carats per year.
that synthetic gems were produced so early often comes as an unpleasant
surprise to those who inherit or purchase a vintage jewelry item.
The heir, or buyer, is expecting that the age of the piece, alone,
guarantees natural origin. Although in more recent years synthetics
are, at best, found in "entry level" jewelry, in the first
two or three decades of the 20th century, synthetics were sometimes
used by noted designers, and high end jewelers, who appreciated them
as signs of "scientific progress" or "modernity".
1910 gold, natural pearl and synthetic ruby ring
their use as synthetic or simulant gems, physicists and chemists make
large quantities of both copies of natural gems, and totally artificial
ones, for industrial and research purposes.
over 90% of the diamond abrasives ("bort") for industry,
used in everything from the saws that cut through pavement, to dentists'
drills, are synthetics produced in a laboratory. Laser and electronic
technologies depend strongly on the properties of laboratory created
crystals. Even a cheapie "quartz" watch has, at its heart,
a synthetic quartz crystal. Lasers based on synthetic crystals are
used in medicine in a wide variety of ways from surgery to removing
tattoos to improving vision.
Beyond these practical applications, laboratory study
and production of synthetic mineral crystals allows scientists to test
hypotheses, and extend knowledge in many areas of the physical sciences.
picture of synthetic diamond crystals used as abrasives
Crystal Formation Processes :-
in Nature, and in the laboratory, there are three basic ways in which
1. Melt (a molten material solidifies)
2. Solution (a solid is precipitated from a liquid in which it was dissolved)
3. Vapor (a solid material condenses from a gas in which it was dissolved)
each of these we can think of everyday examples: if you have ever made
hard candy, you will be familiar with the melt/solidification process,
the calcium deposits on faucets and the water spots on dishes are examples
of crystals derived from a solution, and frost on the window pane is
a commonplace example of the vapor mechanism.
this class we will survey the most widely used gem crystallization processes,
and the types of gems they produce:
1. Flame Fusion
2. Czochralski "Pulling"
each of the melt processes the powdered solid ingredients necessary
to make the gem are brought to their melting point and then allowed
to cool in such a way that a single large crystal or cluster of large
crystals is formed. The three processes, each suitable for making different
materials, differ primarily in the temperatures used, the type of container,
the heat source and the nature of the surface on which crystallization
Flame Fusion :
The process commercialized so successfully by Verneuil, is termed "flame
fusion". It is simple in theory and in practice. Corundum is Al2O3,
crystallized in the trigonal system. All that is necessary is to melt
the raw material, aluminum oxide powder, and allow it to crystallize.
If you want ruby, you just need to add a small amount of chromium oxide
to the mix (Cr is the chromophore that creates red in ruby). Although
the process has been scaled up for today's large factories, it is, in
essence. unchanged since Verneuil's time. Synthetics produced in this
manner are the least expensive, and most commonly used types. So much
so, that over one billion carats per year of flame fusion synthetic
corundum, synthetic star corundum, and synthetic spinel are made.
Verneuil "flame fusion" process for production of synthetic
ingredients fall into a chamber heated to 2200 degrees Centigrade by
an oxygen-hydrogen torch flame. As they fall they melt. Upon reaching
a ceramic rod in the bottom, cooler, area of the chamber, they crystallize.
Slowly the ceramic rod is turned and lowered creating from the melted
corundum a carrot shaped crystal called a "boule". The shape
of the boule is characteristic, and is not one that is found in Nature.
This unnatural curved shape results in severe strain in the crystal
lattice which necessitates splitting the boule in half before it can
be cut. This somewhat limits the size of synthetic gemstones. It is
possible (at considerable extra expense) to use a special slow cooling
regimen, (similar to that used in glass blowing factories) to reduce
strain, so that whole boules can be cut.
Verneuil process takes about 4 hours and results in boules, at maximum,
of about 20 x 70 mm (3/4" x 2 3/4"), weighing approximately
4-500 cts. Various elements can be added to create different colors
(Ti and Fe for blue, for example) and rutile (titanium dioxide), can
be added to create star stones. A special heating and cooling regimen
is necessary for the star stones in order to force the rutile to exsolve
into needles, rather than remaining dissolved.
Flame fusion synthetics are among the easiest types to
identify. Their most characteristic feature is curved growth rings (called
curved striae) that can be seen under magnification with appropriate
lighting. In addition, sometimes coloring is uneven and follows the
growth, making for curved color zoning. In the single crystal gems made
by Nature, there are never any curved growth features or curved color
zoning, so their presence is a dead give away. The presence of bubbles
is also occasionally a tell-tale sign.
Wouldn't you know it?
striae seen in a cut synthetic ruby at 25X, under diffused lighting
It is sad but true that, as consumers and marketplace
watchdogs become more knowledgeable and sophisticated about gems,
the deceivers get trickier. This is the case with flame fusion synthetics
which are being passed off as natural by reheating the cut gems to
near their melting point the growth layers can be partially fused
with the result that the appearance of the curved striae is diminished,
making these pieces harder to identify.
2. Czochralski "Pulling" :
It was the needs of science and industry, rather than those of the
jewelry trade, which prompted the development of the Czochralski "pulling"
melt process. Emerging laser technology demanded larger diameter,
strain-free, higher clarity crystals than could be produced by the
flame fusion process. Only later did the jewelry market begin to eagerly
absorb some of the production.
In this process, the gem source materials are melted
in a metallic (usually platinum) crucible using radio frequency energy.
A thin, flat, seed crystal (either natural or synthetic) is lowered
to just touch the surface of the melt, then slowly rotated and withdrawn
("pulled"). The slower the rate of pulling, the larger the
diameter of the resulting crystal boule.
The seed gives the solidifying materials both a surface
on which to crystallize, and an an atomic scale "pattern"
to follow. This seed area is generally removed before the rough is
Although many exotic materials (like gallium arsenide)
are made for exclusively for industry, YAG, corundum, Alexandrite,
and cat'seye Alexandrite are the major gem materials produced by this
method. Production expenses are much higher than those of the simple
flame fusion process, so the products are more costly as well.
are very difficult to identify microscopically as the crystal that forms
on the seed is usually flawless, and the large diameter of the boule
makes observing the curved striae difficult. On occasion, they may contain
triangular or hexagonal platinum crystals eroded from the walls of the
crucible, which will conclusively identify the piece as synthetic.
simulant for Emerald and Tsavorite Garnet, and a durable, brilliant
material in its own right
The very subtly curved striae seen on a magnified photo (25X)
of the pear shaped green YAG shown above, would be easy to mis-identify
triangular platinum crystals in this magnified synthetic Alexandrite
are a dead giveaway, though
Skull Melting :
The commercial production of cubic zirconia, first accomplished by Russian
scientists in the 1970s, required some ingenuity. The melting point
of CZ is well over 2300 degrees C, which rules out the use of metal
or ceramic crucibles. The problem was solved by using an externally
cooled crucible filled with the powdered ingredients and then heating
it with focused radio energy that melted only the center. The unmelted
material formed its own insulation, or "skull". As the melt
slowly cooled, large, usually flawless, crystals were formed.
present, CZ is the only material produced in this way, and costs are
kept down by the large yields from each batch (currently the retail
price of CZ rough is about $.05 per carat). Various colors are produced,
but for the great majority of CZ is sold in its colorless form as a
it is easy to identify by its optical and physical properties like density,
thermal conductivity, and dispersion, microscopically, there are few
signs of CZ's synthetic origin. Rarely, tell-tale bubbles can be seen.
(I had to examine quite a few CZ pieces before finding this one lone
bubble to photograph).
Colorless CZ, today's diamond simulant of choice, few inclusions
or growth features, other than an occasional bubble, give clue
to the synthetic origin of CZ
Solution processes :-
characteristic feature of these processes is that rather than being
melted, the source materials are dissolved in a solvent (not always
water), and put under high temperature and pressure. The supersaturated
solution is slowly cooled, and the gem crystallizes onto a natural or
synthetic crystal "seed". If the solvent is water, the process
is termed "hydrothermal", if it is another substance, then
the process is called "flux". Because of the high temperatures
and pressures involved, strong sealed metal containers are used to hold
gems, like emerald and quartz, can only be made by solution methods.
In other cases, such as with ruby and sapphire, solution methods are
an alternative method of production.
some of you remember crystal-forming demonstrations in junior high school
science class. If not, the basics of this idea can be summarized by
thinking of the formation of "rock candy".
old fashioned treat is simply very large crystals of table sugar (sucrose)
on a string. It is made by dissolving sugar in hot water until the solution
is supersaturated (more sugar than will dissolve at room temperature).
A wet, rough surfaced string, is rolled in dry table sugar, then hung
in the solution, which cools and from which the water slowly evaporates.
The dissolved sugar then crystallizes on the string. (If no string is
present, the sugar will simply crystallize as a mass on the bottom and
sides of the container.)
As the name indicates, this type of process uses water as the solvent.
The vessel in which the gems form is lined with silver and referred
to as a "bomb". (One can only speculate as to how it got this
nickname, however, if you've ever misused a pressure cooker in your
kitchen, you might have an idea!).
synthetics are relatively expensive, as the equipment used is pricey,
and the yields are small and slow to form (weeks to months). Because
this process so closely mimics what occurs naturally in the Earth's
crust, the majority of inclusions in such gems are natural looking,
making them hard to identify. Occasionally, cut gems will show part
of the seed plate or a distinctive non-natural looking inclusion called
a "nailhead spicule". The primary gems produced by this method
are emeralds, corundum (especially ruby) and quartzes in a variety of
colors including blue.
In some cases the solvent in which the gem source materials are dissolved
is not water, but another material like lead fluoride or boron oxide,
called a . These materials have in common that they have a lower temperature
of cystallization than the gem. As the temperature in the crucible is
lowered, then, the gem crystallizes first, separating out of the still-liquid
flux. The process is slow and expensive. The highly corrosive nature
of the fluxes means that crucibles must be made of a very resistant
metal like platinum, iridium or gold, and the process can take months.
Ruby, sapphire, quartz, emerald, Alexandrite,
YAG and red spinel are the major gems produced in this way. Although
expensive as synthetics go, the resultant gems have natural looking
inclusions, the most notable of which are sometimes called "wispy
veils". Consisting of crystalized flux within minute cracks in
the gem, they are so like natural fingerprint inclusions in their appearance
that it takes a well-trained eye to discriminate them.
"wispy veil" inclusions in a flux grown Synthetic Ruby
Vapor process :-
third possible way to make gems synthetically is by vapor deposition.
At present only diamonds (see below) have been made this way.
"Synthetic" Cabochon Gems :-
discussing the following types of man-made materials, I will be putting
the term, synthetic, in quotes. Although these gem substitutes are chemically
and physically as close to the real thing as it is currently possible
to make them, they still lack some of the crucial attributes of their
natural counterparts. To strictly observe the niceties of gemological
jargon, I should call them simulants, but as they are sold and generally
discussed as synthetics, I'll simply use the quotes.)
this category go "synthetic" corals, turquoise, and opals
all of which, (compared to the true synthetics above) are relatively
easy to separate from natural. Under magnification each of them reveals
its man-made characteristics: the coral lacks the characteristic biological
ultrastructure of natural coral, the turquoise has a slightly bumpy
surface, reminiscent of Cream of Wheat cereal that is most unlike that
of natural stones, and the opal, shows an unnatural and distinctive
"chicken-wire" hexagonal structure that gives it away.
"Synthetic" white Opal, characteristic "Chicken
pattern of "Synthetic" Opals, 25X magnification
first successful synthesis of diamond was accomplished in 1955 by scientists
at General Electric Corporation. These were tiny, .15 mm. crystals meant
for industrial use. By 1958 the cost of synthetic diamond "bort"
was competitive with natural, and today industrially produced diamond
abrasives dominate the market. Besides their obvious superiority as
abrasives, industrial diamonds find other applications as heat sinks
and corrosion protectors. GE is still a major player, but shares the
world market for industrial diamonds with Sumitomo and DeBeers Corporations.
General Electric was also the first to produce gem synthetic diamonds
in 1970. These were small and quite yellow. The nitrogen in atmospheric
air incorporates into the diamond during the formation process, and
acts as a chromophore giving the resulting crystal a yellow color. GE's
method, in essence, attempts to replicate the conditions deep within
the Earth's mantle where diamonds form naturally. Called HTHP (high
temperature, high pressure), this, still somewhat secret process, involves
a metal solvent/catalyst, 60,000 atmospheres of pressure, and temperatures
of at least 1500 degrees C. The machines in which the diamonds are formed
are called "presses". For the last thirty years or so, synthetic
gem quality diamonds have been largely a laboratory curiosity as they
cost more to produce than it would cost to obtain equivalent stones
All this is about to change! Several companies are now involved in producing,
or gearing up to produce, gem synthetic diamonds for the jewelry market.
Gemesis and Chatham are two manufacturers of note : Gemesis is already
in the retail sales mode, specializing in intense yellow colors with
gems nearing 2 cts, while Chatham is poised to enter the market shortly
with pinks and blues as well as yellows.
To date, the high expenses and difficulties in attempting to keep the
yellow color out, have given little motivation for the HTHP manufacturers
to try to compete in the colorless diamond market. Fancy color diamonds
are a much more profitable product. It remains to be seen if the public
will be willing to pay the, still very high, prices (about 30 - 40%
the price of natural fancy color stones) for synthetics.
Gemesis created fancy color Diamonds
created fancy color Diamonds
"Presses" engaged in producing synthetic diamond by
the HTHP method
CVD, Chemical Vapor Deposition
The third of the possible gem synthesis processes (condensation from
a vapor) has been pioneered, by Apollo Corporation, for the production
of diamonds. In this approach, a vacuum chamber (at .1 atm of pressure)
containing a thin diamond seed crystal is filled with methane gas (CH4)
at 1000 degrees C. At that temperature and pressure regime, the carbon
in the gas separates from the hydrogen, and crystallizes upon the diamond
Early on, the resulting crystals, which
were wafer thin, were intended for industrial applications, primarily
as the future generation of heat resistant computer chips. As the methodology
has improved, thicker and thicker crystal wafers have been formed. At
present, Apollo gem quality diamonds of .25 ct have been cut. Compared
to HTHP diamonds, they are relatively white and have high clarity. It
looks as if it won't be long until gem synthetic diamonds are a profitable
side-line for this company.
chamber used by Apollo Corporation for CVD Diamond synthesis
chamber used by Apollo Corporation for CVD Diamond synthesis
does the Diamond world think of all this :-
of the hottest topics of discussion in gemological and jewelry marketing
circles these days, is synthetic diamonds and their potential impact
on the natural diamond market. Although some analysts have been quick
to cry doomsday, and predict the fall of the natural diamond industry,
the majority opinion is that created diamonds were inevitable, and having
arrived, should be viewed as a positive development. Enhanced and man-made
diamonds are expected to share the market with natural origin/natural
color stones, as have synthetic and enhanced rubies, sapphires and emeralds
with their natural counterparts.
major concerns within the industry have been those of 1. disclosure
2. identification and 3. cost.
1. Disclosure :
At present, the major companies producing gem synthetic diamonds have
taken pains to identify their products as synthetic, and are selling
them only through reputable and licensed jewelers. Gemesis for example,
puts a laser inscription on the girdle of all its .25 ct or larger gems.
(Unfortunately, it is a relatively simple matter to remove this ID after
the gem leaves the store, and there is evidence that this is already
2. Identification :
The conclusion that the market is large enough for both synthetics and
natural stones is based on the assumption that the two can be reliably
discriminated. Although HTHP gems have tell-tale features that enable
a well trained and well equipped gemologist or jeweler to identify them,
CVD diamond recognition currently is possible only for major laboratories.
The statement below was issued as part of official press release by
"The major laboratories can conclusively
identify gem synthetic diamonds" William Boyagian, President of
3. Costs : Unlike diamond
simulants which can be detected with a simple, inexpensive electrical
conductivity tester, synthetic diamonds, are diamonds and therefore
pass all the standard physical and optical tests, as diamond.
DeBeers Corporation (the company that
controls the majority of worldwide diamond rough sales) has been in
the forefront of synthetics detection, and offers two table model devices
(costing over $20,000) that can identify HTHP stones. The DiamondSureTM
which tests for a specific 415 nm absorption line, and gives a reading
of either: "natural" or "refer", and the DiamondViewTM
which detects characteristic strain patterns and can conclusively identify
the HTHP synthetics amongst the "referrals".
for sale through GIA-UK, this "DiamondView" TM instrument
can be used to conclusively identify HTHP Diamonds
CVD diamonds cannot be reliably detected
even with these instruments. The average neighborhood jeweler is understandably
concerned about the costs that will inevitably ensue as verification
of natural origin in diamonds becomes the sole pervue of the big labs.
(Testing with Raman Laser Spectroscopy and Fourier Transform Infrared
Spectroscopy at the temperatures of liquid nitrogen, doesn't run cheap).
To grade or not to grade,
that is the question :-
Very heated arguments can be started
among those involved in the diamond business over whether synthetic
diamonds should be graded (for color and clarity) or not. GIA, AGTA
and most other big gem labs have taken the position that they will identify
synthetics, but will not grade them. It is their assertion that synthetics,
have no inherent value, and, as such, should not be graded. EGL (European
Gem Labs) and its American subsidiary, EGL-USA are grading the synthetic
stones for clarity and color. Their philosophy is that customers want
their stones graded, and they are providing a desired service.
Cultured Pearls :
Before discussing cultured pearls, let's
take a brief look at natural pearls. Natural pearls are very rare today,
but they were always rare. The product of a mollusk's reaction to an
irritant, such as a stray bit of shell or a parasite, they take many
years to grow to useable size, and few individuals within a population
of mollusks will ever make them. Beyond that, the majority of pearls
in Nature are small, baroque in shape, and few are blemish free. Throughout
most of history, natural pearls were the rarest and most highly valued
of all gemstones.
Here are some examples of natural pearls
and how they were used. As the vast majority of pearls that were collected
were tiny, those who could afford pearls, but didn't have the budget
of Cleopatra or a Roman Emperor, often used seed pearls (2 mm or under).
Matched strands of larger round pearls, though quite expensive, were
very small by today's standards, and not perfectly uniform in either
size or color.
1870's seed pearl necklace, the tiny pearls are sown onto a mother-of-pearl
backing with horsehair to make the pendant, and strands of them
were twisted for the chain: this was a popular style among elite
brides in Victorian England, a 16" Art Deco Era natural pearl
strand, the pearls grade from 3 mm to 4.5 mm
along came Mr. Mikimoto :
the turn of the 20th century, there were several individuals experimenting
with culturing pearls, and in 1906 the first batch was grown. It remained,
however; for Kokichi Mikimoto to both scale up the process to mass production,
and market the products successfully to an initially skeptical world.
By the end of the 1920's cultured pearls were an accepted part of the
pearl marketplace, and today they are the marketplace. Except for those
found in some antique and vintage jewelry items, and a few natural pearls
sold to collectors, all the pearls in commerce are cultured. "Cultured"
was a term that was hotly debated initially, with many feeling that
the term "synthetic" should be used to clearly specify their
non-natural origin, but Mr. Mikimoto won that fight. (Regardless of
terminology, though, cultured pearls are not natural gems, their origin
is the result of human intervention.).
Types of Pearls :-
are two basic types of pearls (be they cultured or natural). A pearl
that forms within the body cavity of the mollusk, and has a three dimensional
shape, sometimes round, is a "cyst" pearl. One that forms
attached to the shell of the animal, and therefore has a flat back surface
is known as a "blister" pearl. Possible colors of pearls vary
with the species of mollusk, but usually are some shade of the color
of the shell lining of the animal.
assembled, cultured, blister pearl product is known as a "Mabe"
pearl. They are grown by gluing a plastic or shell half dome or other
shape (nucleus) onto the inside surface of a mollusk's shell. Once the
nucleus is coated with nacre, the blister pearl is cut away from the
surrounding shell. The nucleus is removed and the cavity is filled with
an epoxy resin, and backed by mother-of-pearl. Mabe pearls are quite
attractive, less expensive alternatives to cultured pearls of the same
Natural pearls come from mollusks native
to both saltwater (oysters) and freshwater (mussels), and cultured pearls
can be produced from both types of mollusks. Two different strategies
are used in culturing: bead and tissue nucleation.
Saltwater cultured pearls are "bead nucleated", meaning that
a round bead of shell is used as the "irritant" around which
the oyster secretes the nacre. The company that Mikimoto founded is
still going strong, and specializes in the highest quality saltwater
cultured pearls from the Akoya oyster. Such pearls are white to silver
or cream, often with pink overtones. They tend to top out at about 8
mm in size, and those pieces with relatively thick nacre layers due
to long cultivation periods, have a fine luster.
Larger pearls, such as Tahitian blacks
and Indonesian golds, are cultured in oyster species from the tropics,
and can attain sizes of 20 mm or greater. Saltwater cultured pearls
can be rather expensive depending on size and quality.
Akoya saltwater cultured pearls : this 18" strand of 8 mm
round pearls retails for about $3000
mm cultured Tahitian black pearl ring, 10mm is considered small
for a Tahitian and this piece can be had for under $200
the picture below an oyster is being nucleated with a shell bead. You
can see the animal in the holder, and the dish of beads. Expert nucleators
command respect within the industry as skilled professionals, and are
very highly paid.
Freshwater cultured pearls are almost always "tissue nucleated"
which means that only a slice of mantle tissue from a donor mussel is
used to start the culturing process, there is no shell bead. As is the
case with natural pearls, a tissue nucleated freshwater pearl is virtually
all nacre. Historically, freshwater pearls were first produced from
Lake Biwa in Japan, but today most come from China. The original "Biwa"
pearls, introduced in the 1970's were small with flat, baroque shapes
they were sometimes referred to, dismissively, as "rice crispies".
can see in the second photo below that things have changed, and today's
freshwater cultured pearls are large and approach a perfectly round
shape. Freshwater pearls remain inexpensive: the strand at the left
retailed when new (1980's) for about $30 and the 18", 7.5 mm strand
to the right currently retails for under $200.
Original-type Biwa Pearl strand
near round 7.5 mm strand
saltwater cultured pearls can be identified by microscopically viewing
the drill hole and observing the demarcation between the shell nucleus,
and the nacre layer on top of it. In difficult cases, and with freshwater
cultured pearls, Xrays will do the job. The bead nucleus shows up clearly
in the radiographs, as does the smaller area where the mantle tissue
was placed in a freshwater cultured pearl. There is actually little
chance, though, that today's fresh or saltwater cultured pearls would
be mistaken for natural pearls. To anyone who has studied natural pearls,
today's creations are so large, so round, and so well-matched in color,
that the difference is obvious. Making the call between enhanced and
unenhanced is another matter though. As you recall from Lesson 8, most
cultured pearls are enhanced in one way or another.
known as imitation or faux gems, simulants look like what they imitate,
but they don't have the chemical, physical and optical properties of
the gem they mimic. (simulants are only fakes if they are not properly
disclosed.) Some are man-made, and some are natural gems in their own
The history of gem simulation goes back every bit as far as that of
gem enhancement. Since before 3000 years ago Egyptians have been making
faience, a beautiful blue to green non-clay ceramic material. The colors
are derived from copper or other metals and, although used and admired
for its own sake, it has also commonly been used to imitate turquoise
and lapis lazuli.
Faience "mummy" beads, circa 300 BCE (newly re-strung
Victorian "Egyptian Revival" brooch featuring "plique
a jour" enamel and an ancient faience scarab
technology required to make faience is similar to that necessary to
make glass, which the Egyptians also mastered. Glass making skills are
believed to have traveled to the Greco-Roman world from Egypt, and by
1000 BCE, the Romans began casting glass. (Glass blowing came along
fragment of circa 500 CE Roman glass made by blowing molten glass
into a mold (the iridescent surface patina was not a glaze or
paint put on by the Romans, but has been slowly created by chemical
reactions, between the glass and soil, occuring over centuries
of burial, these reactions creates a thin layer of metal oxides)
glass beads and cabochons were in used in jewelry in fact they were
enjoyed only by the wealthy, as these technological marvels of the day
were more valuable than most natural gems.
Circa 1000 CE Chinese glass bead (on modern chain)
bronze and glass cabochon ring Circa 100 CE
Gems as Simulants :-
is very common for one natural gem to be used to imitate another of
similar appearance. For example serpentine, aventurine quartz and hydrogrossular
garnet, all have long histories as jade simulants. Likewise, bone is
a common substitute for ivory, and white zircon has long been enjoyed
as a natural diamond simulant. Red spinel commonly is substituted for
ruby, sodalite for lapis lazuli, and copal for amber.
Bone Carving (ivory)
Red Spinel (ruby)
Copal, a natural, geologically younger, partially fossilized tree
Simulants: Glass and Plastic
Although its historical roots go way back, glass is still one of the
most popular gem simulants today. Glass, itself, is an amorphous material,
but its main raw material, silica sand (quartz), is crystalline. In
glass-making sand is mixed with certain other materials and melted;
then it is cooled so quickly that crystallization doesn't occur. Some
scientists describe glass as a liquid that is so stiff that it behaves,
superficially, like a solid. This assertion is supported by the observation
that very old glass windowpanes are thicker at the bottom than at the
top, and the older they are, the more this effect is seen.
quite different forms of glass are used to simulate gems: crown glass
and flint glass.
Crown Glass: is used for ordinary windows and bottles, and is also known
as common, or silica glass. When gems are made from it, it is often
called "paste". This sort of glass is relatively soft, has
a low refractive index, a low specific gravity, and virtually no dispersion.
Due to its lack of brilliance (a consequence of the low refractive index),
a metallic foil or paint was often applied to the back facets of such
gems (called "foilbacks") to increase reflectivity.
Flint Glass :
Is also known as "crystal", "strass" (named after
the 18th century inventor), or "leaded glass". This very soft,
easily scratched glass has a high refractive index, high specific gravity,
and high dispersion.
natural color of glass is a light green (perhaps you have seen or remember
the color of the original "Coke" bottles), but it can be de-colorized
or colorized chemically. By adding different colorants (chromophores),
spectacular hues can be achieved, like purple (manganese), dark blue
(cobalt), and red (gold).
Identifying glass :
Many paste gems are molded rather than faceted, and as such, have notable
surface characteristics, such as sunken facets, an orange peel surface,
or mold lines. Even if glass is faceted, its softness often results
in facet edges that are slightly, to noticeably, rounded compared to
the knife-edge facets of harder gems.
Physical and optical characteristics are also useful in identifying
glass. The typical bubbles and swirls, seen under magnification, have
already been mentioned in Lesson 5. Added to this are the low hardness
(4-6, depending on the type of glass), the characteristic brittleness,
and the conchoidal fracture with its vitreous luster. Furthermore, the
relatively low thermal conductivity of glass makes it feel somewhat
warmer in the hand than crystalline materials. As an amorphous substance,
glass will give a polariscope reaction of SR, and in terms of density
the specific gravity of crown glass is less than most common gems, while
the specific gravity of flint glass is higher.
glass has been used to imitate just about every kind of gem. Today,
however, glass is most commonly used to simulate translucent gems such
as opal and chalcedony, and opaque gems like jet, lapis and coral. (Over
the last 100 years or so, the availability of synthetic gems has dramatically
decreased the popularity of glass "rubies" and other faux
transparent gems). Even phenomenal gems such as moonstone, sunstone
and pearls have glass simulants. Faux pearls had their heyday of popularity
before the advent of pearl culturing, but many types are still made
today. Commonly they are made of translucent glass beads that get a
many-layered coating of lacquer containing pearly looking "essence
d' orient" (made from ground fish scales!).
moral of the story for the gemologist is: "Always suspect that
the "gem" you are looking at is glass and test for this possibility."
Foil-backed glass "Rhinestones" Circa 1950
glass Jade simulant showing typical bubbles under magnification
Man-made Aventurine glass, "Goldstone"
Obsolete glass Opal simulant"Slocum Stone"
made of a modern glass opal simulant, "Opalite"
A glass faux Pearl showing scratches in the painted-on surface
Most people would be surprised to learn how far back the manufacture
of plastics goes. By the late 1800's the "plastic age" was
well into its beginnings. The earliest plastics, like vulcanite, Bakelite,
celluloid and lucite were used for a wide variety of purposes, including
among them gem simulation. Some of these early materials found use as
imitations of jet, ivory and tortoise shell, making copies of these
luxury organic gems available to a large audience. Plastic jewelry peaked
in popularity in the 1950's, but still finds use today, mainly in the
cheapest of simulants (the sort you might get from a gumball machine,
or as a prize at a carnival).
plastics can be recognized by the greasy to sub-vitreous luster, rounded
facet edges, surface craters or pits, and the presence of mold marks.
The surface of its fracture has a dull luster. Microscopically, plastics
have swirls and bubbles similar to those seen in glass. They give an
SR reaction to a polariscope test.
are quite soft, with hardnesses ranging from 1.5 to 3, and both the
refractive index and specific gravity are low. Even more so than with
glass, the low thermal conductivity of plastics makes them warm to the
touch. When touched to the surface of plastic, a "hot point"
tester will release an acrid chemical smell that is quite distinctive.
(Here's a method of identification that I wouldn't recommend with a
prize antique: drop the piece from about 5 inches onto a hard surface
like a desk top. Plastic makes a hollow sound compared to the higher
pitched, sharper sound made by either glass or crystalline gems.)
is a more convincing simulant of transparent gems, but plastic does
a good job imitating translucent and opaque stones like amber, turquoise
and coral. (A sizable percentage of the least expensive Southwestern
sytle "turquoise" jewelry is actually plastic.) Certain optical
properties of some types of plastic can be utilized do a good job of
simulating phenomenal gems like opal and moonstone.
PLASTIC GEM SIMULANTS
Faux Pearl (note mold mark)
plastic Moonstone drops on a glass "crystal" bead bracelet
AND VINTAGE PLASTIC SIMULANTS
Circa 1870's Vulcanite brooch (jet)
1890's Celluloid brooch (ivory)
plastic "moonstone" dress clip
bad news in regards to diamond simulants is that there are a multitude
of them, no other gem has been so often imitated. The good news is that
all of these mimics can be discriminated by either simple observation,
or by basic gemological testing no big labs needed.
oldest diamond simulants were glass, and colorless natural gems. With
glass, first came the older crown type (usually with a foiled back to
increase reflectivity), and later the more brilliant and dispersive
flint glass. The natural gems white topaz, sapphire, zircon and quartz
were also used, but at a higher cost than glass.
(If you are skeptical that glass or quartz could make a reasonable approximation
of a diamond, consider that with the simple early diamond cutting styles,
and the polishing technologies available prior to the 20th century,
diamonds were not the blindingly brilliant gems of today.)
diamond simulants enter the picture around 1910 when colorless sapphire
was first produced by the flame fusion process. This was followed by
the introduction of colorless synthetic spinel (1920), synthetic rutile
(1948), strontium titanate (1955), YAG (1960), CZ (1976), and Moissanite
SIMULANTS NATURAL AND SYNTHETIC
Identifying Diamond Simulants :-
Crown glass is notably softer, less dense, less brilliant, and less
dispersive than diamond. Flint glass though dispersive, is more dense,
and much softer. Both types have a vitreous luster, as opposed to the
adamantine luster of diamond.
Natural Gems :
Depending on the species, the RI, the density, or the dispersion would
be the give away, and all the commonly used colorless natural gems are
DR, so a polariscope test would easily separate them from the SR diamond.
Zircon, the closest to diamond in appearance is not only DR, but so
strongly birefringent that it shows doubled rear facet images when viewed
with a loupe.
Synthetic Sapphire/Synthetic Spinel :
Although hard, corundum is a DR gem and its RI of 1.76 (diamond's is
OTL), and lack of dispersion is telling. As spinel is an SR gem a polariscope
test wouldn't help, but its RI of 1.72, hardness (8), and low dispersion
would be the best indicators.
Synthetic Rutile/Strontium Titanate :
These gems enjoyed a period of brief popularity after their introductions,
and are sometimes seen in vintage pieces. Indentification is a simple
matter though, as their extremely high dispersion makes them very easy
to spot, and their softness makes them noticeably fragile compared to
Although hard (8.5) and SR, YAG is so lacking in dispersion that it,
too, can be easily separated from diamond.
The remarkable popularity of CZ is, in my opinion, well deserved: hard
(9), SR, and not too noticeably more dispersive than diamond, it passes
most visual tests well, but testing for density will reveal it every
time, as it is much heavier than diamond.
(In addition, all of the simulants above will "fail" a thermal
This is the latest contender, and like CZ, it is hard (9.5), and not
so overly dispersive as to be obvious. It will pass a thermal conductivity
test as diamond, but its electrical conductivity will invariably identify
it. In light of this, a new generation of "diamond testers"
is being highly promoted as indispensable to those concerned with guarding
against bogus "diamonds".
Such equipment not really necessary though, as Moissanite is DR, and
will flash "on and off" with the polariscope test. Even without
fancy gemological equipment, all that is needed is a loupe, and a little
knowledge. Moissanite gems are deliberately cut on an optic axis so
that when you look down through the table you see sharp facet reflections
(no doubling) as if the stone were SR. By tilting the gem on its side,
and viewing the back facets with a loupe, the strong birefringence of
this DR gem will reveal itself by the presence of doubled facet images,
something you'd never see in a diamond no matter which direction you
view of doubled facet reflections in Moissanite
Assembled Gems :
Also known as composite gems, assembled
gems are made of two or more pieces of gem material joined together.
They can be used as to simulate (or fake) another gem, or just for their
own sake, for example to make an artistic gem creation, or to make a
particular gem material more durable or useable.
Assembled Gem Art :
Intarsias, insets, inlays, pietra dura and micro-mosaics fall into the
category of making something beautiful out of what would otherwise have
been waste products. These lovely works of gem art are often made of
the small bits and pieces left over from, or too small for, other lapidary
Black Onyx/precious Opal intarsia
Black Onyx/rock crystal assembled carving
Citrines with Garnet insets
18th century "pietra dura" (hard stone) style intarsia
Micro-mosiac (glass) brooch
close up of micro-Mosaic
Increasing Durability :
Doublets and triplets are generally made either to increase the durability
of a fragile gem or to support and protect a thin slice of gem material.
Usually a doublet consists of a thin layer of some valuable, fragile,
or rare gem material backed with a thicker layer of something sturdy,
and less expensive. If the piece is unmounted, or set in prongs, it
is usually very easy to see the demarcation line between the top and
the bottom. Sometimes the backing is simply used to provide contrast
or create an artistic effect. A triplet is a doublet with a third, top,
layer made of a tough transparent material like colorless quartz.
Black Opal doublet
piece black Opal doublet viewed from the
side at 10X
Triplets (note black bottom layer and colorless top layer)
Quartz doublet with a green Gaspeite bottom layer
Gems as Simulants and Fakes :
Historically, assembled gems were more important as gem simulants and
fakes in the days before synthetics became widely and inexpensively
available. You are more likely to see them in vintage and antique jewelry
pieces., but there are still a few cases, where assembled stones are
used as gem stand-ins, and some unscrupulous folks are still trying
to pass some types off as something they aren't.
for Deception :
Mabe pearls, as described in the cultured pearl section above, are examples
of assembled gems which are produced with no intent to deceive. They
always have flat backs and mother of pearl bases which easily distinguish
them from regular cultured pearls.
Tahitian Mabe Pearl earrings
The green stone below is a simulated
"Soude" emerald such as is regularly used in the marketplace
today. Usually, at least at the retail level, there is no intent to
deceive, and these are sold widely and openly as an imitation May birthstone
Soude is actually a three piece assembled gem a triplet. The top and
bottom layers are made of colorless synthetic spinel created by the
inexpensive flame fusion process. The middle layer, depending on the
manufacturer is either green glass or, as in the stone below, green
glue. Because the stone is faceted, when viewed from the top with light
reflecting throughout its interior, selective absorption from the green
layer makes the stone look uniformly green.
It is not uniformly green, though, as
you can see in the second photo, where the stone has been immersed in
liquid and is viewed from the side. The colorless top and bottom are
clearly visible. Once the stone is set however, such a test is difficult
Another "tell" for an unmounted
or prong mounted piece of this type, is the magnified view of the girdle
area. As the third photo below shows, the "join" or seam between
the crown and pavilion, is visible. In a single-piece gem, no such line
would be there, the girdle area would be unbroken.
Imitation "Soude" Emerald (a synthetic spinel triplet)
Immersed side view
Deception Intended :
The classic case of deception with
an assembled stone is the "garnet and glass doublet" which
was used throughout the 19th and early 20th centuries to mimic various
colored transparent gems. In these clever concoctions, the bottom and
most of the top of a piece of "rough" is constructed from
colored glass to which a thin slice of natural (red) garnet has been
fused or glued. The rough is then faceted so that the thin sliver of
garnet forms some of all of the crown area of the gem. The color of
the glass pavilion is all that shows face up, especially when the doublet
is mounted. The garnet top provides high luster and good durability
that the glass bottom lacks.
By microscopic examination, or immersion
and viewing from the side, the deception can be seen, but once mounted,
these frauds almost always escape detection.
today's marketplace there are still a few doublets and triplets being
manufactured to fool the unwary, but due to the low cost and easy availability
of synthetics, they are not as common as they once were. Some examples
that jewelers and auction houses occasionally still see are YAG/strontium
titanate doublets (as diamonds), synthetic ruby/ruby doublets (as ruby),
and beryl triplets (as emerald).
Contemporary synthetic Ruby, Ruby doublet showing "join"
at the girdle
Vintage garnet and glass "sapphire" shown under immersion
and as a microscopic view of the crown area
1910 Garnet and glass "emerald" ring
Assembled Stones :-
assembled stones can be as easy as simply looking at them, as in the
case of intarsias or inlays, but in other cases careful testing is necessary.
The best bet for a gemologist, jeweler or collector is to always check
the RI of both the crown and pavilion of the stone, and observe both
the crown and girdle area under magnification and under immersion if
possible. Prong mounted gems can usually be examined adequately as is,
but bezel set stones (especially those with completely closed backs)
often must be dismounted if their identity is to be conclusively verified.