Cubic Zirconia - Defined
Cubic Zirconia (CZ), a diamond simulant, is not only
the oldest diamond substitute, but also the most popular. Composed of
zirconium oxide (ZrO2) the mineral is extremely rare in
natural form. Discovered by German mineralogists in 1937, zirconium
wasn’t considered economically feasible. That changed in the 1970s,
when a Soviet scientist learned how to grow zirconium in a laboratory.
First marketed in 1977 under the trade name "Djevalite", Cubic
Zirconia didn’t become widely popular until Swarovski & Co., the
world-renowned producer of leaded crystal, began mass producing it the
1980s.
Today, CZ is considered by gemologists to be the best
available diamond substitute. The similarities of cubic zirconia to a
diamond are so remarkable that even gemologists can’t always tell
the difference when viewed with the naked eye.
Cubic zirconia possesses less brilliance (less sparkle), but has more
fire (flashes of rainbow color.) CZ is also very hard, not quite as
hard as a diamond, but like a diamond can scratch glass. Though
measured in carats like diamonds, a more accurate measurement of cubic
zirconia would be in millimeters.
Cubic zirconia is much heavier, weighing in at 75% more than diamonds.
For example, a 6.5mm cubic zirconia is equal in size to a one-carat
diamond, but actually weighs 1.75 carats. Additionally, and an
important measure of the difference, cubic zirconia is a thermal
insulator, whereas diamonds are thermal conductors.
What made it possible in the 1970s to produce cubic
zirconia was the invention of the microwave. Yes, the technology that
created the now common household appliance was used to create cubic
zirconia.
Specific heat (the temperature required to melt a substance) of cubic
zirconia is 2,750 degrees centigrade. The extremely high melting
temperatures prevented using a conventional crucible (a vessel made from
a high temperature metal for melting materials at high temperatures). No
crucible in existence could handle the heated zirconium.
As a result of microwave technology, the then USSR perfected a method to
contain CZ in its molten state, such that the material formed its own
crucible. In a process called the skull melt, the material heats up from
the inside outwards. The outside remains relatively cool while the
inside melts, forming its own outer crust or “skull”. When the heat
is switched off, the product cools under rigidly controlled conditions
and hardens. As it hardens, cubic zirconia crystals are formed,
typically 5 cm long by 2.5 cm wide. They are then cut and faceted to
produce the finished gemstone.
At the time, the Russians, at the time didn’t posses enough natural
rubies, which were essential in the manufacture of lasers. Producing
cubic zirconia was an experiment to create a stone with the optical
properties similar to those of a ruby to prevent the need of importing
the expensive stones.
The production of cubic zirconia was an attempt to reduce the cost of
laser technology, not to produce a diamond substitute. The Russians
published their breakthrough in 1973, and commercial production of cubic
zirconia began in 1976. Four years later, global production had reached
50 million carats, 10,000 kilograms, annually.
During their attempt to create a cheaper laser, the Russians discovered
an important detail. If synthesized without heat, zirconium oxide will
create elongated rectangular style crystals. Only with extreme heat is
the preferred cube form obtained. Once cooled, however, the zirconium
wants to return to its natural form, so a metal oxide stabilizer is
added to the process to ensure isometric or cubic crystals.
The amount and type of stabilizer used depends on the individual
manufacturer. As a result, the brilliance and hardness of the finished
cubic can vary, so measurements for color, etc., are given in ranges.
- Color
C - F (on the diamond scale)
- Hardness
8-8.5 (Mohs hardness scale)
- Specific Gravity (Relative Density)
5.5 - 6.0
- Crystal Form
Cubic (Isometric)
- Refractive Index
2.15
- 2.18
- Dispersion
0.058 - 0.066
Because they’re grown in a lab in a controlled
environment, the cubic zirconia crystals are also perfect in structure,
without feathers or inclusions. If an imperfect crystal is formed, it
simply isn’t used. If a colored stone is desired, oxides can be
introduced into the production process to create a rainbow of cubic
zirconia. The greatest market value, however, is in simulating diamonds,
so the majority of cubic zirconia is left colorless.
Due to the hardness and clarity of cubic zirconia, it can be cut using
the same proportions used in cutting fine diamonds. Faceting, too, is
intensive and precise, creating hundreds of facets, mimicking the
brilliance of diamonds.
In recent years, however, manufacturers have tried different ways to
distinguish their product by attempting to “improve” cubic zirconia.
Amorphous Diamond is one such innovation, coating finished cubic
zirconia with a film of diamond-like carbon (DLC). The result is defined
as harder, more lustrous, and more diamond-like. Thought to dim the
excess fire of CZ, DLC supposedly improves the refractive index--more in
line with diamonds--and having a diamond signature under Raman
spectroscopy, a device which identifies an object’s crystal structure.
Another technique is vacuum-sputtering an extremely thin layer of metal
oxide (usually gold) onto the stones to create iridescence. Marketed as
“mystic” the material is unlike DLC, in that it isn’t permanent.
The metal oxide layer is easily removed by abrasion.
Because of its hardness and durability, caring for cubic zirconia
doesn’t require any special cleaners or brushes. A good liquid jewelry
or ultrasonic cleaner will do. Detergents and soap can leave a film on
the stones, as can skin oils, but if care is taken to thoroughly dry and
to minimize contact with the skin; cubic zirconia can last a very long
time.
Though often considered to be less fine because it’s created instead
of found, cubic zirconia can be a fine stone on its own. It’s
colorless (or white in diamond terminology), it’s pure and it’s
durable. Not a diamond, certainly, but definitely a beautiful and
economical alternative.
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