Glimmering
Gems offers the following information to our visitors to assist them in
making educated decisions about gemstones and Metals. Please contact us
should you have any question about the material provide below.
The most
commonly used concepts in grading diamonds are Cut, Clarity, Carat, and
Color. Each one of these is addressed in more detail below. NOTE: The
so-called 4C's of diamonds are not enough to completely value a diamond, and
the information provided here is for reference only. We recommend you
consult a jewelry professional before purchasing high end diamonds.
Color - All diamonds are graded on a color scale ranging from D to Z,
with D being colorless, and Z being very yellow. For example, see the color
scale and table below. The most common diamond colors are G and H. (Note. due to limitations of computers, these colors are only
approximate)
Clarity - Diamonds are also judged by the size and
amount of inclusions (defects) in the stone. Geologically, an
inclusion is "a solid fragment,
liquid globule, or pocket of gas
enclosed in a mineral or rock."
In gemmology, this definition is
usually extended to include any
other feature of the gemstone
which impedes the free passage
of light through the stone. This
includes changes in crystal
growth direction (e.g.
twinning), and external
features, such as fissures which
run from the surface into the
stone, naats , trigons, and
zones of color absorption (e.g.
the very common color banding
seen in sapphire). Not all inclusions are visible
either with the naked eye, or
under the standard 10 times
magnification used by
gemmologists. Many consumers
believe that inclusions are
things which are visible to the
naked eye, and that if no
inclusions can be seen, then the
stone is perfect. Some stones
contain many areas of
"twinning", where the growth
direction of the crystal has
changed during its formation,
and these areas can absorb or
refract light in such a manner
as to reduce the brilliance of
the stone. Other stones contain
large numbers of small
inclusions, some visible under
10x magnification, others not,
because they are too small.
These clouds of microscopic
inclusions can reduce the
passage of light through a stone
so severely that the stone looks
"dead", with no brilliance or
fire whatsoever. Such stones
usually have a slightly cloudy
look to the naked eye. In
recent decades, the GIA,
Gemmological Institute of
America, has influenced other
gemstone grading bodies, such as
CIBJO, throughout the world, and
most countries now use the same
standards as the GIA for diamond
clarity, so that the GIA scale
has become virtually an
international standard. There
still remain vast differences
between commercial grading and
laboratory grading. The European
Gemlogical Laboratory is also
recognized as a worldwide
standard.
Symbol
Name
Definition/Comment
Eye Clean
FI
Flawless
Completely flawless
inside and outside
viewed with 10x
magnification
IF
Internally Flawless
No inclusions viewed
with 10x magnification
VVS-1
Very
Very Small Imperfect
Some inclusions that
are very difficult to
see when viewed with 10x
magnification
VVS-2
Very
Very Small Imperfect
Some inclusions that
are very difficult to
see when viewed with 10x
magnification
VS-1
Very
Small Imperfect
Some inclusions that
are somewhat difficult
to see when viewed with
10x magnification
VS-2
Very
Small Imperfect
Some inclusions that
are somewhat difficult
to see when viewed with
10x magnification
SI-1
Slightly
Imperfect
Some inclusions that
are fairly easy to see
when viewed with 10x
magnification or the
naked eye
SI-2
Slightly
Imperfect
Some inclusions that
are fairly easy to see
when viewed with 10x
magnification or the
naked eye
Difficult to see with
naked eye
SI-3*
Slightly
Imperfect
Some inclusions that
are fairly easy to see
when viewed with 10x
magnification or the
naked eye *Not part of
the GIA scale, but often
used by the European
Gemlogical Laboratory
Carat - Diamonds are weighed and cataloged according to their
carat weight, often abbreviated as CTW. (one Carat = 0.20 Grams). Sometimes
a diamond is also weighed on a
point scale (100 points = 1
Carat). And as if that did not
add enough confusion, sometimes
the unit of Grain is used (1
Grain = 25 Points). Be sure to
not confuse the use of Points as
a unit of weight versus Points
used to describe the diamond cut
as described below. The size of
the diamond is related to the
carat weight, but it does not
scale exactly, meaning that a
2CTW diamond is not twice the
size of a 1CTW diamond.
The table below gives the
approximate diameter of a
perfectly proportioned brilliant
cut diamond and the approximate
carat weight.
Carat Weight
Diameter (mm)
Carat Weight
Diameter (mm)
0.05
2.4
0.9
6.3
0.1
3.0
1.0
6.5
0.2
3,8
1.25
7.0
0.3
4.4
1.50
7.5
0.4
4.8
1.75
7.9
0.5
5.2
2.0
8.2
0.6
5,5
2.50
8.9
0.7
5.8
3.0
9.4
0.8
6.1
5.0
11.2
It is possible to estimate the
carat weight from measured
dimensions of other cuts as
well, but the accuracy is
diminished. The carat weight of
a diamond can only be measured
precisely by weighing it,
however this is very difficult
to do once the stone has been
placed in a setting. Unless you
are obtaining jewelry direct from
the manufacturer, all carat
weight values are approximate,
and deviation of the estimated
value from the actual weighed
value by +/- 5% is considered
acceptable.
Cut - Diamonds come in many
different shapes, or cuts, some of which are indicated below. The choice of
cut is a personal preference,
with the round brilliant cut
being by far the most popular.
The cut of a diamond is one of
the things that influences the brilliance (or fire) of
the stone. More important is
that the stone is properly cut
so as to reflect light back out
of the diamond. Improperly cut
stones can significantly reduce
the brilliance or fire of the
stone.
The amount of reflected light is
controlled by the table depth, which is the measurement from the top of the
stone to the tip. Proportions determine a diamond's brilliance (amount of
light reflected back to your
eye), fire (the flashes of color
due to prismatic separation into
the colors of the rainbow) and
scintillation (sparkling
movement of light as you move
the diamond). Below are the
approximate proportions to
create a round diamond of
maximum beauty, achieving an
excellent balance between
brilliance, fire and
scintillation. (NOTE: These
proportions only apply to round
diamonds)
Gold is the most popular material used in jewelry
today. There are many different grades and colors of gold, and consumer
tastes vary widely around the world. In its purest form, gold is practically
unusable in making jewelry because it is much too soft. To make the gold
harder and thus workable into jewelry, it is alloyed with other metals. The
process of alloying is simply mixing metals together. Because the value of
the jewelry is controlled by the amount of gold in the alloy, a scale was
developed to keep track of the amount of gold and other materials, and today
this is known as “karats.” The table below indicates some common karat
values found in jewelry, and the amount of gold contained in the alloy. The
lower the karat value, the more durable, or hard, the jewelry will be, but
it will contain less gold.
Label
Parts Gold
Percent Gold
Fineness (European)
Comment
24k
24/24
99.9%
999
China, Hong Kong, Taiwan
22k
22/24
91.6%
916
India
18k
18/24
75.0%
75
Designer jewelry
14k
14/24
58.5%
585
Most common
10k
10/24
41.7%
417
US minimum
9k
9/24
37.5%
375
UK standard
8k
8/24
33.3%
333
Germany minimum
The choice of material used in the alloying process
not only affects the hardness of the gold, but it also affects the color of
the gold. The table below lists some of the commonly used metals in alloying
with gold, and their effect on color.
Metal
Color Effect
Copper
Reddening
Silver
Greening
Zinc
Bleaching
Nickel
Whitening
Palladium
Whitening
For example, to make white gold, a jewelry maker would
generally mix Gold with Copper, Nickel, and Zinc. White gold is also often
treated with a thin layer of Rhodium to keep its luster. It is important to
realize that the choice of alloying material has very little effect on the
value of the gold in the jewelry.
Platinum is a very rare material, and can be
considerably more expensive than gold. Like gold, platinum must be alloyed
with other metals to make it suitable for making jewelry. The choices of
alloying metals are Iridium, Ruthenium, and Palladium. The choice of
alloying metal has no effect on the value of the Platinum jewelry. The
amount of alloying material is closely regulated, and generally is limited
to 5 or 10% of the overall weight. 95% pure Platinum is labeled as either
PLAT 950 or PT 95. 90% pure platinum is labeled as PLAT 900 or simply PLT.
Palladium is part
of the Platinum family of metals. It has seldom used in jewelry making
because of its relatively low oxidizing temperature, but it is making a
fashionable recovery. Palladium jewelry can be
considerably more expensive than gold or other metals. Palladium must be alloyed
with other metals to make it suitable for making jewelry, typical choices
are Ruthenium and Platinum. The choice of
alloying metal has no effect on the value of the Palladium jewelry.
Unfortunately, the labeling of Palladium jewelry has not been standardized,
and it is typically just stamped Palladium. Watch out for the unscrupulous
jeweler who might sell Palladium jewelry as Platinum.
Silver is a common, inexpensive alternative to gold and
platinum jewelry. In its purest form, Silver will rapidly oxidize or
“tarnish” when exposed to air. For this reason, it is commonly allowed with
copper to form a mixture of 92.5% Silver and 7.5% Copper. This is commonly
labeled as 925, and nearly all silver jewelry is made from this alloy.
Titanium is a relative new comer to the jewelry
industry, but is gaining praise for its light weight, durability, and
hypoallergenic nature. Jewelry grade Titanium is often an allow containing
varying degrees of Aluminum, Vanadium, and Tin. The most common grades of
Titanium are listed in the table below.
