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MICHAEL APPLER
Rio de Janeiro - BRAZIL
GEM CREATION AND ENHANCEMENT
Gem Creation and Enhancement
Historically gem possession has been reserved for wealthy, royalty,
or high religious leaders. It has always been human nature to want
what others possess, so imitation gems have been common for some 4,500
years, in the form of glass, plastic, composites, and treated gems. It
is not against the law to imitate, as long as the true identification
is given. It is only fraud when imitations, natural or synthetic, are
passed off as a more valuable gem at an inflated price.
Is It Real? Created Imitations Synthetic Gemstones
Composites Treated Stones
Is it real?
"Is it real?" is a question often posed to jewelers or the
knowledgeable gem enthusiast, when people view gems. You do not have
to be an expert to answer this question, of course "it" is real! The
"real" question should be, is this gem natural or material created in
a laboratory? After the inital answer is given, one should ask, "What
difference does it make?" Imitations and synthetics simulate the
genuine gems and minerals and can be quite beautiful. Part of the
definition of a gem is the beauty and this is a subjective attribute.
If these created stones and imitations are properly labeled as such,
and priced accordingly, they can be an affordable alternative to the
"real thing!"
The definition of synthetic is material created in a laboratory using
basically the same ingredients found in the natural products (Matlins
and Bonanno, 1998, p. 123). Some synthetics have no natural
counterpart. Synthetic gems have identical physical, chemical, and
optical properties as the natural gem material, for the most part. An
exception to this, is in the coloring chemical for some synthetics,
which can be different from the natural coloring agent. Even though
synthetics may replicate the natural gem, they must be identified and
prefaced with "synthetic," "created," or some origin indicator.
An imitation is an artificial likeness or copy, which could mean a
synthetic material or natural gemstone. Imitations are not exclusively
synthetics and not all synthetics are meant to imitate some gem. Some
synthetics are marketed as a "gem" in their own right, such as CZ or
cubic zirconia (usually advertised without a "synthetic" preface; it
does have a counterpart in nature, but it is extremely rare). The term
imitation is usually applied to glass and plastic although it can
refer to natural minerals too. Golden-colored quartz or citrine has
imitated topaz in birthstone rings for so long, many people have a
difficult time accepting the natural colors of topaz, which are
colorless, pink, pale brown, sherry-colored (reddish-orange), and less
commonly "yellow."
Created Imitations
Imitations usually resemble the gemstone in color only and are easy
to identify as an imitator. "Ancient Egyptians were the first who
feigned gemstones with glass and glaze, because genuine were too
expensive and/or too rare" (Schumann, 1997, p. 242). One of the
earliest imitations to resemble turquoise, prized by Egyptians, and
some 7,000 years ago they constructed a turquoise-colored ceramic
substance, termed faience, that was used for beads, amulets, pendants,
and rings (Matlins and Bonanno, 1997, p. 227). Also, blue glass gems
were found in King Tut's tomb (Matlins and Bonanno, 1997, p. 227).
Glass is amorphous or a created, inorganic substance which is mixed in
a molten form and cooled to a rigid form without crystallizing. There
are two main types of glass: crown and flint. Crown glass is made with
silica, soda, and lime. It is used for bottles, window and optical
glass, and costume jewelry. Flint glass is composed of silica and
soda, and lead oxide or other metal oxides replacing the lime. This
type of glass has been called strass (or stross) after the Austrian
who is credited with its discovery, Joseph Strasser. Flint glass was
used to substitute for diamond and because of this, was prohibited in
the 18th century by Empress Maria Theresa (Schumann, 1997, p. 242).
Glass imitations have been referred to as "paste," which is from the
Italian "pasta" meaning dough ..."because the ingredients are mixed
wet to assure uniformity of the batch" (Hurlbut and Kammerling, 1991,
p. 150).
Stones cut from flint glass resembles the gems they are meant to
imitate because lead gives a greater dispersion and higher refractive
index. Coloring glass is accomplished using a metallic oxide with a
purple color associated with manganese; blue with cobalt; red with
selenium or gold; yellow and green with iron; red, green, blue with
copper; green with chromium; yellow-green with uranium; and "amber
glass" with a combination of manganese and iron, and no amber at all!
"The final color of the glass is also affected by such factors as the
type of glass used, the oxidizing or reducing conditions used during
manufacturing, and annealing after manufacture. Colorless glasses are
made by adding decolorizing agents called glassmaker's soaps; these
reduce the greenish tint that otherwise ensues from iron impurities."
(Hurlbut and Kammerling, 1991, p. 151) Many cheap glass imitations are
"foiled", that is the pavilion facets covered with a thin metallic
film that acts as a mirror to enhance brilliance and sparkle.
Colorless glass can be given a face-up color, or color looking down
at the crown, by covering the pavilion with a colored film. A
translucent look can be achieved by adding tin oxide.
Glass "Opal"
The Slocum stone, developed by John Slocum, is an interesting
imitation of opal. It is glass that has various body colors of white,
black, near colorless, or orange (fire opal). The "flashes" of color
are produced with metal foils (looks like colored cellophane in
transmitted light) that resemble parts of a puzzle (Hurlbut and
Kammerling, 1991, p. 153). Opal synthesis succeeded in the US. in 1970
(Schumann, 1997, p. 152). Enhancements can be made by coloring black
or matrix opal or impregnating opal with artifical resin (Schumann,
1997, p. 152).
Goldstone
Goldstone is colorless glass with flecks of precipitated copper
crystals, which result in the glittery aventurescent phenomenon. Deep
blue and green "goldstone" can also be found.
Cat's Eye Glass
Fire Eye is made of ..."parallel, tubular gas bubbles produced by
aeration, the same process used to carbonate soft drinks" (Hurlbut and
Kammerling, 1991, p. 153). Other glass cat's eye material is produced
by fused optical glass fibers, some with distinct hexagonal cross
sections for the "fibers" giving it an overall honeycomb effect.
"Still another chatoyant glass, Victoria Stone, is partially
devitrified and exhibts a silky texture in the recrystallized areas"
(Hurlbut and Kammerling, 1991, p. 153).
Color Change Glass
Alexandrium is a trade name for glass that changes from pink to
violet in incandecent to fluorescent lighting; Tourma-like is a trade
name for glass that changes from pinkish orange to gellowish green in
incandescent to fluorescent lighting (Hurlbut and Kammerling, 1991, p.
153).
Glass Pearls
Some 300 years ago, hollow glass beads were lined with essence
d'orient, an iridescent material from fish scales, and filled with wax
(Hurlbut and Kammerling, 1991, p. 153). Translucent white glass beads
with coatings of essence d' orient serve as imitations today. Glass
and imitation plastic "pearls" will feel smooth when rubbed lightly
against front teeth, while cultured and natural pearls feel gritty
(Hurlbut and Kammerling, 1991, p. 153). "Until 1945, Gablonz and Turnau
in Czechoslovakia were important centers for the glass-jewelry
industry. Then this tradition was taken over by Neugablonz in Allgau,
Bavaria." (Schumann, 1997, p. 242). Porcelain, enamel, resins, and
plastics also serve as gem imitators. Plastics are formed by heating
and/or molding, and called celluloid (cellulose lastic), bakelite
(phenol-formaldehyde), plexiglass or lucite (methyl methacrylate
resins), polystyrene and polyvinyl resins. The plastic is constructed
of long, chainlike molecules called polymers and have a very low
hardness. They are sometimes faceted but usually cut en cabochon to
imitate gems such as amber, turquoise, jade, to name a few.
Synthetic Gemstones
The first gemstones to be synthesized occurred in 1838, although they
were only of scientific interest (Schumann, 1997, p. 243). A French
chemist, A. V. Verneuil, succeeded in producing gem quality synthetic
rubies in 1888, termed a flame fusion process (Schumann, 1997, p.
243). The method melts a powdered aluminum oxide with dye additives,
and the molten material forms in a pear-shaped "boule." Although it
has no crystal faces, the crystalline structure is identical to the
natural gem. Synthetic blue sapphires were produced by 1910 and
sometime later, colorless, yellow, green, and alexandrite-colored
sapphires were perfected (Schumann, 1997, p. 243). Star rubies and
sapphires were created, by adding rutile to the smelting, in 1947.
Synthetic spinels have been produced since 1910, with the verneuil
process, although the chemical composition varies from the natural
spinel; synthetic emeralds have been produced since the 1940s
(Schumann, 1997, p. 246). Industrial quality, diamond synthesis
occurred in Sweden and the United States by 1953-4; gem quality
synthetics were perfected in the 1970s. A German chemist, I.
Czochralski, developed another synthesis method in 1918, where the
boule is drawn out of the smelting after a crystal nucleus has been
created. While rotating the boule is continually drawn upward and
grows on the underside also. In recent years crystals have been
"flux-grown," a created method that more closely resembles natural
crystal growth. These laboratory-grown synthetics are more expensive
to produce than other methods, but can still make a good alternative
for consumers who are unable to afford natural gemstones (Matlins and
Bonanno, 1998, p. 124).
Some synthetic imitations of diamond include: synthetic rutile (also
known as titania or diamonite, created in 1948); fabulite
(occasionally called diagem, created in 1953), stronntium titanate
(SrTiO3); YAG (also called diamonaire, created in 1969), yttrium
aluminum garnet (Y3Al4O12); GGG or galliant, a gadolinium gallium
garnet, (Gd3Ga5)O12; djevalite, a calcium zirconium oxide (ZrO2/CaO),
linobate, a lithium niobate (LiNbO3), cubic zirconia (also known as
fianite, phianite, or KSZ), and yttrium zirconium oxide (ZrO2/Y2O3)
(Schumann, 1997, p. 242-3, 246). Most recently moissanite, silicon
carbide, has become a popular diamond imitation (developed in
colorless gem quality in 1996, produced by Cree Research Inc.,
distributed by C3 Inc.) (Nassau, McClure, Elen, and Shigley, 1997, p.
261).
Composites or Assembled Stones
Doublets, triplets, and foil backs are composite stones, or assembled
from two or more components. Although they can be assembled to
deceive, some composite stones were devised to overcome low hardness
or durability of a gem. Doublets are made of joining two pieces with a
colorless cement or fusion. Triplets are two layers of colorless
material joined by colored cement that imparts the overall color, or
three layers with a colorless cement. Foil backs are made by applying
a mirror like back to the stone, foil or metallic paint, to enhance
the dispersion and brilliance or produce a star-like effect. Genuine
doublet or triplets are composed of the same stone on the top and
bottom, such as a light-colored beryl joined by a layer of deep green
emerald cement. The genuine assembled stone was composed of two pieces
of the same gem and used to imitate that gem (e.g., a beryl triplet
may consist of two pieces of colorless beryl joined by a green colored
cement and meant to imitate emerale). Semi-genuine doublet or triplet
has only one portion genuine (usually the crown) or of the species it
imitates, such as an emerald imitation with a colorless beryl crown,
quartz pavilion and deep green cementing agent. False doublet or
triplet is when one (or more) portion is a natural material but none
is the gem it is meant to imitate, such as the garnet-glass doublet
meant to imitate a ruby or quartz joined with green cement to imitate
emerald.
Garnet and glass doublet was once a commonly encountered composite
stone, especially before synthetics became routine. Glass is fused to
a slice of garnet (usually almandine). Garnet is usually found in the
crown for color and durability. Garnet and glass doublets have been
constructed to imitate garnet and diamond. Other doublet imitations of
diamond include: foil-backed glass, rhinestones (foil-backed rock
crystal quartz), and colorless spinel or corundum with a pavilion of
strontium titanate. Corundum doublets, meant to imitate ruby and
sapphire, can be natural corundum crown glued to a synthetic corundum.
Emerald triplets, meant to imitate emerald, consist of natural
colorless beryl, colorless quartz, or colorless synthetic spinel,
joined with a green cement.
Opal and ammolite (fossilized shell of ammonites in form of
aragonite) are found in thin veins or structures. When used as
jewelry, these two gems are commonly found as doublet or triplets to
increase its durability and make to most of the rough material
recovered. It is common to cement a thin slice of opal or ammolite to
a backing. The backing could be a piece of common opal, black glass,
or black dyed chalcedony. The triplet would be assembled the same way,
except with a convex cap of clear quartz, glass, synthetic spinel, or
synthetic sapphire is cemented to the top of the opal or ammolite
section.
Rare Composites
Diamond and diamond doublets are called "piggy-back" diamonds.
Another diamond doublet involves a diamond crown and colorless quartz,
synthetic sapphire, synthetic spinel, or glass on the pavilion.
Jadeite triplets are constructed of a colorless jadeite hollow
cabochon glued to a flat base, with the hollow dome filled with a
green jellylike substance (Hurlbut and Kammerling, 1991, p. 162).
Imitation cat's eye could be assembled from a hollow cabochon of
synthetic corundum, filled with fibrous ulexite (often called TV
stone!), glued to a base of a shallow cabochon of synthetic corundum.
The opal imitation could be a cabochon of colorless glass or plastic
glued to a base of mother-of-pearl shell.
Treated Stones
Enhancing natural colored gemstones has been going on for hundreds of
years. Treatments are frequently applied to enhance the color,
although practices are also common to disguise clarity imperfections
also. Changes can be temporary or permanent. Treatments may involve
heating, diffusion, irradiation, fracture and cavity filling, coatings
and impregnations, dyeing, bleaching, and laser drilling.
Heating
Heat altered gem material is changes or improves the color. Some heat
treatment is permanent and can lighten, darken, or completely change
the color of the gem. Some heat treatment is unstable and can revert
to the original pretreated color with time. Zircon can be unstable and
after heat treatment the stones can be exposed to sunlight for several
days and then stored in the dark up to a year to remove the unstable
stones (Hurlbut and Kammerling, 1991, p. 169).
Heat treatment may change crystal inclusions within the gem, causing
them to melt or explode. This may be detected with magnification by a
skilled person, although it may be difficult to definitively state any
color is natural when the gem material is flawless.
Temperatures used for heat treatments vary, depending on the material
and desired color. Sometimes low temperature, such as that from an
alcohol lamp, will change brown topaz to pink; very high temperatures,
as high as 2050 degrees C, are needed for other alterations, such as
titanium-rich milky sapphires to blue.
Amber
Amber is heated to change water bubbles to discoid fractures
(disk-like or radiating), known as sun spangles; heating can also
change lighter yellow amber to darker reddish amber. Cloudy amber,
with tiny gas bubbles, may be clarified with heating while it is
immersed in an oil (e.g., rapeseed or linseed oil).
Beryl
Heating aquamarine, blue-green variety of beryl, will remove "yellow"
and turn the stone to a more desirable blue; this same treatment is
done with morganite, turning the stone from peach to a pink beryl. "In
both these cases it is believed that the heating converts
yellow-color-producing Fe3+ to Fe2+, the latter having no effect on
body color when it occurs in the structural sites in which the Fe3+
produces the yellow coloration" (Hurlbut and Kammerling, 1991, p.
166). This process is not easy to detect, nor is the heating of yellow
to light brown chalcedony (which contains iron) to produce red
carnelian (converting limonite to hematite).
Corundum
"The heat treatment of corundum is one of the most widespread and
commercially significant of gemstone enhancements. It is generally
believed that the vast majority, if not all, of the blue sapphires and
rubies seen in the jewelry trade today have been subjected to one or
more high-temperature heatings" (Hurlbut and Kammerling, 1991, p.
166). Heating is done to induce or intensify the yellow in golden
sapphire; these treated sapphires lack the typical, strong orange
fluorescence (long-wave UV) of untreated yellow sapphires. Heat
treated blue sapphires could be detected by presence of discoid
fractures, patchy color zoning, or a chalky greenish fluorescence
(short-wave UV). Heating titanium-rich corundum and cooling slowly
may result in acicular rutile to exsolve to create asterism.
Quartz
Heating quartz is common, to lighten purple and brown coloration
(reversing the radiation-induced crystal structural damage), or to
produce citrine (yellow to orange quartz). Bi-colored quartz can
result, termed ametrine, with both purple and yellow quartz. Heating
purple quartz can create green, marketed as prasiolite. Heating golden
tiger eye can produce a red variety (dehydrating the limonite to
produce hematite).
Topaz
Brown to orange topaz is colored in part because of chromium, and
also because of crystal structure damage. Heating this topaz repairs
the structural damage, reducing the yellow component, and turning the
brown to orange topaz pink. The material has stronger dichroism than
untreated pink topaz. Topaz that is irradiated produces a crystal
structural damage, creating a yellow and blue color; heating follows
irradiation, reducing the yellow component, and leaving blue as a
final color.
Zircon
Reddish-brown zircons can be heated to 900-1000 degrees C, in a
reducing atmosphere, to produce blue, colorless, or some undesirable
color. The undesirables are then heated in an oxidizing environment,
converting them to colorless or yellow, red, or orange colors.
Tanzanite
Tanzanite, an important gem variety of zoisite, is strongly
pleochroic, exhibiting violet, blue, and yellow to green. The
yellow-green component is removed with heating, resulting in the blue
or purple final color. It is assumed that all tanzanite is heat
treated.
Smoking
Smoking is a technique used exclusively on opal. Opal is wrapped in
brown paper and charred, which causes a thin dark brown coating that
intensifies the fire or play-of-color. When the coating wears off, the
"black" opal appears brown. It is easily detected with wetting the
gem. Whereas natural opals show the same fire wet or dry, the smoked
opal's fire diminishes when wet but returns when dry.
Diffusion
Diffusion treatment is a process which alters the color by exposing
the surface to certain chemicals and heating. It has only been
successful with corundum, especially with blue sapphire. Faceted
stones that did not respond to heat treatment alone, are coated with a
slurry of aluminum oxide plus iron and/or titanium (if want blue),
chromium oxide (if want red or pink), nickel compound (if want
yellow). The stones are heated to temperatures that approach melting
and the color-causing agents diffuse into the stones, creating a thin
layer of color (Hurlbut and Kammerling, 1991, p. 169). The color is
confined to the surface and does not penetrate throughout the gem,
which could present a problem if the gem was chipped and needed to be
recut (Matlins and Bonanno, 1998, p. 126).
Radiation
Artifical irradiation is the most controversial process used to alter
a gems appearance and many times the colors are not stable in light or
low heat. Health risk is a concern, as there are still questions about
the acceptable levels of radioactivity a gem can carry. The Nuclear
Regulatory Agency is currently working on establishing standards.
"Commercially three types of facilities are used to treat gemstones:
gamma ray facilities (often using cobalt-60), linear accelerators
(producing high-energy electrons), and nuclear reactors (producing
high-energy neutrons) (Hurlbut and Kammerling, 1991, p. 170). The GIA
Gem Trade Laboratory can test gems and grade for acceptable or
unacceptable radiation levels (Matlins and Bonanno, 1998, p. 126).
Radiation is energy emitted in the form of particles or
electromagnetic rays. Ionizing radiation creates crystal structure
defects, which can take colorless beryl and turn it to golden beryl or
heliodor and intensify the pink or red in tourmaline. Intense yellow
or orange colored sapphire is irradiation induced, but the color is
not stable.
"The first documented artificially irradiated gemstone was diamond,
in which a green color was induced by burying the stone in radium
salts" (Hurlbut and Kammerling, 1991, p.170). Unfortunately this
produced residual radioactivity, making the stone too radioactive to
be safe. Neutron and electron irradiation are preferred methods today
for coloring diamonds. It may be very difficult to diagnose
irradiation vs. natural color in diamond with the exception of blue.
Natural blue diamonds are colored by boron and are electrical
semiconductors, while irradiated blue diamonds are electrical
insulators.
Irradiation is also used on quartz for a smoky brown to black color.
Pink spodumene can be irradiated to produce the green variety, known
as hiddenite, but it is not a stable color. Blue topaz is the most
commercially produced irradiated gemstone in today's market. Natural
blue topaz is pale but radiated material creates a deep blue, referred
to as "Electra Blue," "Swiss Blue," and "Max Blue," among other names.
Irradiating topaz may produce a secondary yellow to brown color that
is converted to blue with heat treatments. "Linear accelerator (linac)
treatment is a preferred enhancement method for topaz today (Hurlbut
and Kammerling, 1991, p. 171). Darker blues are attained, called sky
blues, and the process must be followed by heating. The "London Blue"
coloration is created using irradiation from nuclear research
reactors, which produces residual radioactivity causing the material
to be stored until the induced radioactivity decays to acceptable
levels.
Fracture and Cavity Filling
Filling fractures and cavities with a substance having a refractive
index closer to that of the material (as opposed to air), makes breaks
less noticeable, which improves transparency and/or clarity but not
color. Fracture filling can be colored but this is considered under
dyeing.
Emerald
Emerald has the longest history of fracture filling, due to its
popularity and its tendency to be highly included and fractured.
Natural oils have traditionally been used for fillings, such as Canada
balsam, cedarwood oil, mineral oil, cooking oil, and even motor oil!
Cleaning the stone and heat can remove these oils. Recently synthetic
resins have been used, such as Opticon, which is more permanent than
the natural oils. Treated surfaces are best detected with
magnification, in reflected light; dark-field illumination is best for
internal break fillings. A flash effect, blue (indicates epoxy resin),
orangey-yellow (probably epoxy resin), or yellow (sometimes the
residue left after the filling has come out), can confirm the
prescence of resin. Flattened gas bubbles can be trapped in the
filling material, slight colored outline of the fracture, and/or areas
of low relief can be clues to fracture filling.
Diamonds
Fracture filling, or clarity enhanced diamond, effects the clarity
grading of diamonds and is a concern in the trade. The process was
begun in the 1980s and is a method of filling cracks with a glass-like
substance to improve the overall appearance. The filling material is
stable with routine cleaning, but not at temperatures and conditions
needed for jewelry repair. The fillings might up the clarity grade but
have been slightly yellow, lowering the color rating. Some of the time
laser drill holes were made to reach an internal fracture in order to
fill it, or introducing a "fracture" that was not originally there!
Detection of fracture fillings in diamond include: an orange flash or
blue or green flash interference effect with dark-field illumination;
a melted or flow structure in filled breaks; flattened trapped gas
bubbles in the filling material (fingerprint pattern); crackled
texture in the filling resembling cracks on a dry riverbed (Hurlbut
and Kammerling, 1991, p. 173-4).
Other Material
Opal can dehydrate producing surface crazing. These breaks can be
concealed with oil or wax. Chatoyant tourmaline has parallel tubes
creating the phenomenon, that can fill with debris from the fashioning
process or from wear. The stone can be cleaned with acid and then
tubes filled with wax or Opticon resin.
Another filling enhancement introduced in the 1980s was filling
cavities and pits on the surface of ruby, sapphire, and emerald. These
fillings were not oils or waxes, but a glassy material that served to
conceal the cavity and also add weight to the reported caratage of the
stone.
Colorless Coatings and Impregnations
The purpose of coatings is to protect dye treatements, to improve the
polish by masking small scratches, grainy textures, or surface
irregularities, and to stabilize porous gemstones (Hurlbut and
Kammerling, 1991, p. 174-5). These treatments are used on gem material
composed of more than one mineral, such as jadeite, nephrite, or lapis
lazuli, to aid in polishing. Aggregate gem surfaces may be uneven and
vary in hardness. Gems coated because of low hardness include
alabaster, marble, rhodochrosite, soapstone, turquoise, serpentine,
and amazonite feldspar. Besides low hardness, some gems are porous and
the coatings keep the surface from accumulating skin oils and dirt.
Colorless coatings include waxes, paraffin, and plastics. To detect
coatings, a hot needle may cause wax and paraffin to liquify and
flow, whereas platics will have an acrid odor.
Colored Coatings and Impregnations
Colored surface coatings usually add a superficial color layer that
does not penetrate the gem's surface. This enhancement can be detected
with magnification if scratches, pits, or nicks appear in the coating.
Some blue or purple substances have been used to treat yellowish
tinted diamonds to make the stone appear more colorless. The color is
usually applied to the pavilion, just below the girdle, a kind of
treatment like the material used to coat or tint optical lenses.
Another surface coating applied to quartz crystals is a thin layer of
gold, which creates a greenish blue color with iridescence. Colored
impregnations have been employed to change white opal into black opal
and to change the colors of marble and soapstone.
Dyeing
Dyeing is a treatment that alters the body color of a gem and has
been done for thousands of years. For the dye to penetrate, fractures
must exist. If the gem is not porous or fractured naturally, the
opening for the dye to enter the stone is produced by "quench
crackling," a heat-induced thermal shock, that creates a network of
fractures (Hurlbut and Kammerling, 1991, p. 175). The stability of
dyed gems is dependent upon the type of dye, which varies from natural
organic material to synthetic or precipitations of metallic salts.
Emerald and Ruby
Emerald and ruby is dyed using a colored oil, which fills in
fractures and enhances the depth of color. To detect this enhancement,
examine the stone in diffused transmitted lighting and look for color
concentrated around fractures. Some green colored oils will fluoresce
a greenish yellow.
Quartz and Chalcedony
Colorless quartz can be "quench crackled" and placed in the dye
simultaneously or after drying. Magnification can show the result of
the quench crackling. Chalcedony, a cryptocrystalline quartz, has many
varieties including agate, onyx, carnelian, chrysoprase, and
pseudomorphs after bone and wood. The stone is simply soaked in a
solution for penetration, then soaked in another solution to arrive at
the desired color. Chrysoprase is a natural green colored by nickel,
whereas the solution to dye chalcedony green has chromium oxide. This
can be detected by spectroscopy or using the color filter (chromium
colored will be red and nickel colored will remain green). Blue
chalcedony is dyed with cobalt and again can be detected with the
color filter, which will show red. Blackening is a technique using a
sugar-acid chemical reaction that produces carbon to blacken the color
(Matlines and Bonanno, 1997, p. 208). The method is to soak the stone
in a sugar solution, then in concentrated sulfuric acid. This
treatment produces "black" opal and dyed black chalcedony, sold as
black onyx. Ths treatment cannot presently be detected but because
natural gem-quality black chalcedony is extremely rare, this dye
treatment is the norm (Hurlbut and Kammerling, 1991, p. 177). Jasper
may be dyed blue to resemble lapis lazuli.
Jadeite and Nephrite
Green and lavender jadeite is routinely enhanced with dying inferior
material. Green enhanced jadeite can be detected with spectroscopy.
Lavender jadeite, created by dying white jadeite, has no conclusive
tests to detect the enhancement although some fluoresces a strong
orange with long-wave UV radiation. Nephrite has a more compact
texture and is not dyed as often as jadeite.
Lapis Lazuli
Lapis lazuli is an aggregate of minerals which include white calcite
and pyrite. The white calcite can take a dye to create a more uniform
blue. Some dyes can be detected by rubbing the gem with an
acetone-dipped cotton swab, unless the gem has been surface coated
after dying.
Other Gems
Alabaster, coral, banded calcite, marble, and magnesite are dyed to
enhance their color or to imitate. Howlite, a hydrous calcium
borosilicate, is a white mineral frequently found with black veins
that is dyed to imitate turquoise as seen below.
Bleaching
Bleaching is used to lighten or remove color and is done with
chlorine compounds or concentrated hydrogen peroxide (Hurlbut and
Kammerling, 1991, p. 179). This enhancement is done to pearls, black
coral, and chatoyant tiger's eye (in an effort to imitate cat's eye
chyrsoberyl).
Laser Drilling
Laser drilling is used to remove dark inclusions primarily from
diamonds. If the heat does not vaporize the inclusion, the hole is
flushed with hydrofluoric acid. These holes may appear as whitish
channels or as light flashes if a high refractive index material is
used to fill the cavity.
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