What Are
Gemstones?
Gemstones
are generally minerals that have been, or may be, fashioned to
use for personal adornment.
A
gemstone is a mineral, rock , or petrified material that when
cut or faceted and polished is collectible or can be used in
jewelry. Others are organic, such as amber, which is fossilized
tree resin, and jet, a form of coal.
What Makes Color?
Color is the most obvious and
attractive feature of gemstones. The color of any material is
due to the nature of light itself. Daylight, often called white
light, is actually a mixture of different colors of light. When
light passes through a material, some of the light may be
absorbed, while the rest passes through. Those that are not
absorbed pass through or are reflected back, giving the gem its
color. Each gem has a unique color "fingerprint" (known as its
absorption spectrum) but this is only visible when viewed
through a spectroscope. To the naked eye, many gems look the
same color.
Faceting
The most usual method of
fashioning a gem is to cut the surface into a number of flat
faces, known as facets. This gives the stone its final shape, or
cut. The gem cutter, or lapidary, tries to show the stone's best
features, taking into account its color, clarity, and weight.
Brilliant Cuts The
brilliant cut is the most popular for diamonds and for many other
stones, particularly colorless ones. It ensures that maximum light is
reflected out through the front, giving brightness and fire. Variations
in the outline give the oval, the pear-shaped pendeloque, and the
boat-shaped marquise or navette.
|
 |
|
|
Step Cuts
The step cut (or trap cut) shows colored
stones to advantage, having a rectangular or square table facet and girdle,
with parallel rectangular facets. The corners of fragile gems may be
removed, making octagonal stones (for example, most emeralds).
|
Mixed Cuts Mixed-cut stones
are usually rounded in outline, with crowns (above the girdle) cut as
brilliants and the pavilions (below the girdle) step cut. Sapphires,
rubies, and most transparent colored stones are cut in this style.
|
 |
.
|
Fancy Cuts
These have several possible outlines, such as triangular,
kite-shaped, lozenge-shaped, pentagonal, or hexagonal. The cut may be used
for rare gems or to make the most of a flawed or irregularly shaped gem.
 |
Clarity
Clarity refers to
the internal flaws (inclusions) or the external blemishes of a
stone. A flawless colored gemstone is rarer than a flawless
diamond. However, even though clarity is important, it does not
carry the premium that perfection has with diamonds. For
example, a valuable emerald will be heavily included because of
the natural formation process, resulting in many natural flaws
in even the most expensive of emeralds. In addition, lighter
colored stones need to be cleaner, as their flaws show up more
easily. Darker colored stones can hide their defects easier
because of the depth of their color. Most gemstones will have
tiny natural irregularities called inclusions. Most inclusions
are not visible with the naked eye, usually you need to use 10X
magnification to see these inclusions, however larger ones can
be seen with the unaided eye. These irregularities may be
substances such as an unfilled cavity, a small crystal, a
fracture, or a growth pattern within the gem.
The location and
the type of the inclusion or blemish is what are important with
colored stones. If there is a large crack on the surface of the
stone, it may weaken the stone's durability. A large crack would
probably detract from the stone's beauty and reduce its value.
However, if the crack is small and positioned in a less
noticeable area in the stone, then it will not affect
durability, beauty, or price as much as a prominent flaw.
Click here to see gemstone
grading chart
Diamonds
Colored Stones
Carat
Weight is an important quality of gemstone
value. Often the larger the stone, the more valuable it is. An
important thing to remember is that qualities such as color and
saturation are also important in determining a stone's value.
Around 1920, the metric carat was adopted as an international
standard. One carat equals a fifth of a gram (0.20 gram), or
five carats to the gram. Since the late 14th century there has
been a law for diamonds that is known as the 'Indian Law' or
'Tavernier's Law': Wt² x C = Price per Stone.
Pricing in the real world is not that simple because other
qualities such as clarity and color factor in to determining the
price of a gemstone. Remember that size and weight are
different. Size refers to the physical space or volume that a
stone occupies, while weight refers to the gravitational pull of
the object.
The Story of Chatham
Chatham created
gemstones are considered to be nearly identical to natural gems.
The chemical, optical, and physical characteristics are exactly
the same. The only difference is that one comes from the earth
and the other from a lab.
In 1938, Carroll F. Chatham, a young
scientist from San Francisco, California, discovered the secret
to growing gems after much hard work and research. By
duplicating the conditions deep within the earth, such as the
appropriate temperatures, chemical solutions, and pressures,
Chatham realized that he could be capable of growing gems in his
laboratory. Ever since his discovery, he pushed forward and was
determined to continue experimenting and research. In 1949 he
began doing research on the secret of growing Ruby and after
almost ten years he introduced the Chatham Created Ruby. The
ruby was so identical to a natural stone that the only way to
make a positive identification was by conducting tests on the
stones. Chatham Created Gems, now ran under Carroll’s son
Tom, has perfected methods for creating Alexandrite, Sapphire,
Opals, and in 2004, Diamonds.
Resources:
- Stuller, Inc.
“The Diamond and Gemstone Book” Volume 46, Pg. 144
- Applefield Direct
Westminster, Maryland USA
http://www.applefielddirect.com/adj_library.cgi?dlt=on&tt=2790
Gemstone Criteria
Cut
Carat
Clarity
