GEMS - TRADING IN GEMS AND PRECIOUS STONES, MINING PROPERTIES.
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What is Diamond?
The difference is caused by the different types of bonding between adjacent
atoms to form different types of crystalline structure.
In diamond, each carbon atom is bonded to four other carbon atoms in
a tetrahedral structure, like a pyramid. Each link or bond is the same
length, and the tetrahedral formation is therefore completely regular.
It is the strength and regularity of this bonding which makes diamond very
hard, non-volatile and resistant to chemical attack.
Theoretically a perfect diamond crystal could be composed of one giant molecule of carbon.
Carbon is a non-metallic element with the atomic number of 6, and an
atomic Weight of 12. In combination with oxygen and hydrogen it is contained
by all living objects. In the form of graphite it appears black or dark
gray, opaque, and is very soft, whereas in the form of diamond is it clear,
colourless, and extremely hard. In fact diamond is the hardest known naturally
occuring substance.
Carbon has a density of about 2.3 and diamond about 3.5.
There are many different aspects of materials which could be considered
as a measure of hardness. Hardness can mean resistance to scratching, indentation,
bending, breaking, abrasion, cleavage, or fracture. It is easy to confuse
durability or toughness with hardness.
A very simple example is to consider a glass ball and a rubber ball.
Glass is harder than rubber, but rubber is more durable. Try bouncing both
on a hard floor, the glass ball will shatter, whereas the rubber ball will
bounce.
The aspect of hardness which is measured by Moh's test is the scratchability
of a mineral.
Other scales of hardness include Brinell's and Vicker's.
The hardness of each mineral relative to the others varies according
to which test is performed, and also hardness can vary according to the
grain direction, or crystallographic orientation, of the specimen. We have
given typical Brinell hardness figures for each of the minerals in the
table. Diamond's hardness cannot be measured on the Brinell scale, because
a diamond indenter is used for the test itself, but it is many times harder
than corundum.
Sapphire and ruby are the well known varieties of corundum.
Amethyst, citrine, rock crystal, and cairngorm are all varieties of
quartz.
Generally, high scratch resistance is desirable for gemstones, and a
Moh's hardness of 7 or higher is important. The principal reason is that
a common cause of abrasion is sand, which is silica grit (quartz), and
is commonly present in dust. Stones which are softer than quartz are not
suitable for everyday use as facetted jewellery gemstones, particularly
in rings, although many are beautiful and attractive.
Some gems, such as pearls, coral, turquoise, lapis lazuli, amber, and
opal are quite soft, but are usually polished into cabochons or beads,
rather than facetted, and therefore do not show scratches so easily. All
these gemstones have been successfully used in jewellery for many centuries.
ABOUT THE CUT
IDEAL CUT
This determines the "sparkle" of your diamond by reflecting light through
a complex prism of angular cuts. There is an industry standard "ideal cut,"
but simply looking over your stone should be enough: if it sparkles, it's
a good cut. Dull diamonds are often cut too deep or too shallow.
CLARITY
Clarity refers to the absence of inclusions (imperfections)
in the stone.
FL / IF Flawless or Internally Flawless.
VVS1 / VVS2 Very, Very Small Inclusions.
Requires 70X magnification to clearly see inclusions.
VS1 / VS2 Very Small Inclusions.
Requires 30X magnification to clearly see inclusions.
SI1 / SI2 / SI3 Small Inclusions.
Requires 10X magnification to clearly see inclusions.
I1 / I2 / I3 Imperfect-Eye-Visible
Inclusions
When you buy a diamond logically, you can avoid needless
expense. The difference between finding an inclusion in a diamond at 70X
magnification and one at 10X magnification is absolutely nothing to the
naked eye. However, this difference is likely to double or perhaps triple
the price of your stone. Since diamonds are marketed to be a direct reflection
of your love ... young couples are often persuaded to purchase a stone
that is beyond their means. Private Diamonds has the inventory to accomodate
all clarity demands, but we will never push a VVS1 when an SI1 looks the
same without the aid of a microscope.
CLARITY GRADING SCALES COMPARISON
COLOR
Color defines brilliance or purity of the stone's hue.
An absence of color is considered the purest, and most expensive.
Color is often seen differently depending on other factors.
For instance: by using a platinum setting , your diamond will look more
pure by a factor of 2 or 3 shades. Before you buy the purest stone, consider
where it will end up - you probably won't need the most expensive color
to get the best look.
COLOR GRADING SCALES COMPARISON
DESCRIPTION
EGL
GIA
ARGYLE
COLORLESS
0+
D
D
0 E
E
1+
F
F
NEAR COLORLESS
1
G
G
2 H
H
3 I
I
4
J
J
FAINT YELLOW
--------------------------------------------------------------------------------
FAINT BROWN
5
K
K
6 L
L
7
M
M
VERY LIGHT YELLOW
--------------------------------------------------------------------------------
VERY LIGHT BROWN
8
N Light Champange
C1
9
O
10
P
11
Q
LIGHT YELLOW
--------------------------------------------------------------------------------
LIGHT BROWN
12
R Light Champange
C2
13
S
14
T
15
U
16
V
17
W Medium Champange C3
18
X
19
Y C4
20
Z
YELLOW
--------------------------------------------------------------------------------
BROWN
FANCY YELLOW
--------------------------------------------------------------------------------
FANCY BROWN Dark Champange
C5
C6
CANARY
--------------------------------------------------------------------------------
COFFEE
FANCY INTENSE YELLOW
--------------------------------------------------------------------------------
FANCY INTENSE BROWN Fancy Cognac C7
Frequently Used Terms
Alluvial
All deposites laid down on land by the process of erosion
American cut
Same as Ideal cut
Appraisal
A monetary evaluation usually for insurance or estate purposes. An
insurance appraisal is based on an estimate of the retail replacement value.
An estate appraisal is an estimated realization from a quick sale.
Baguette
A style of step cutting for a small rectangular stone. May also be
tapered at one end.
Bearded girdle
If, during the cutting process, the girdle is rounded up too quickly,
tiny, numerous, hairlike fractures extending into the stone will result.
The surface of the girdle will lack the waxy luster and smoothness of a
finely rounded diamond. It will appear fuzzy.
Bezel
The small part of the top sloping surface just above the girdle.
Bezel facets
The eight large facets on the crown whose upper points join the table
and lower points the girdle
Blemish
Surface imperfection. e.g. nick, knot, scratch, minor cavity or poor
polish. An extra facet or a natural on the girdle are also considered blemishes.
Body color
The color of the diamond observed under diffused light against a colorless
background.
Bort
Industrial quality diamonds
Brilliant cut (round)
The most common cut of diamond consisting of 58 facets.
Canary diamond
A fancy yellow, greenish-yellow or orangy stone.
Carbon spots
A term used in the trade to refer to any black appearing imperfection
in a diamond. May be graphite or other dark mineral or even dark reflections
from cleavages or included transparent crystals.
Chip
Term used for a small single cut diamond.
A curved break on a diamond's surface.
Cleavage crack
Generally the most damaging type of imperfection affecting durability
as well as beauty. It is a break that usually extends to the surface although
sometimes they will extand a short distance from an inclusion.
Cloud
A group of tiny white inclusions that together give a cottony or cloudy
appearance.
Colorless
Devoid of body color.
Crown
the part of the diamond above the girdle.
Culet
The tiny facet at the lower tip of a diamond.
Cushion cut
A square cut with rounded corners. An older form of the brilliant cut.
Dispersion
The property of diamonds to seperate white light into spectral colors.
Emerald cut
A form of step cut. usually rectangular but may be square. the number
of steps can vary. Will emphasize color.
Facet
The plane, polished surface placed on a diamond.
Feather
A cleavage or fracture resembeling the shape of a feather.
Fire
Flashes of the spectral colors as a result of dispersion.
Fisheye
A diamond whose pavilion is very shallow, producing a glassey stone
with poor brilliance.
Flaw
A general term used to refer to any imperfection in a diamond.
Fluorescence
The property of changing one type of radiation to another. For example:
UV rays from natural light excite the atoms in certian diamonds causing
them to emit visible light (be lumimescent) .
Fluorochromatic
When fluorescence causes a diamond to change color when exposed to
two different kinds of light. A yellow stone (under incandescent light)
may appear bluish under daylight.
Full cut
A term for a diamond having 58 facets, consisting of 32 and a table
above the girdle and 24 and a culet below.
Girdle
The outer edge of a diamond usually grasped by the mounting.
Girdle facets
The 32 facets immediately above and below the girdle.
Inclusion
Any visible internal foreign object, or any crystal or grain of the
same material as diamond or any break in a diamond.
Irradiated diamond
A diamond that has been exposed to radiation. Irradiation causes the
color of a stone to change. Usually to greenish. May be from a natural
or man provided source.
Kimberlite
The host rock in all primary diamond deposites.
Knot
A diamond crystal embeded in the surface of a host diamond that has
been polished or cut.
Loupe
Small magnifying glass
Lumpy girdle
Unnecessarily thick girdle.
Macle
Flat, triangular, rough diamond which is a twinned crystal.
Melee
Diamonds under .20 carat.
Old English Cut
Single cut
Old European Cut
Early round cut characterized by a very small table, heavy crown and
great overall depth.
Old Mine Cut
An old cut that is square with rounded corners
Phosphorescence
Property of some diamonds to continue to emit visible light (be lumimescent)
in darkness after exposure to UV rays. To glow in the dark. This is a rare
property.
Point
100th of a carat.
Polished girdle
As implies, a polished surface of the girdle as opposed to a waxy one.
It may also be faceted.
Scintillation
Alternating display of reflections from the polished facets of a diamond
as seen by an observer as the stone, light source or the observer is in
motion.
Spread stone
A stone that has been cut with a large table and a thin crown.
Step cut
All facets in a step cut stone are four sided and in steps, or rows
both above and below the girdle. All facets are parallel to the girdle
and except for those on the corners are long and narrow.
DIAMONDS CUTS
Cut is one of the most important factors in a diamond's brilliance. Since it's all about light optics and the ideal angles to produce the maximum effect the cut is critical to a the beauty of the diamond. The closer a diamond is cut to ideal proportions, the greater brilliance the diamond will exhibit.
Many people confuse cut with the shape of a diamond. The shape you select is a matter of individual taste, and today your choice is only limited by the skill and imagination of the craftsman. It is their effort during every stage of the fashioning process that reflects the maximum amount of light back to the eye.
Most round, brilliant-cut or fancy-shaped diamonds possess 58 carefully angled flat surfaces, called facets, whose placement will affect the fire, brilliance and ultimate beauty of your diamond.
The cut of a diamond is in direct conjunction to the proportion of a diamond.
With proper cutting the light passes through the top, reflects off the sides, and then travels back out through the top, giving the diamond optimum brilliance. If the diamond is cut too shallow, light passes through the bottom of the diamond.
If the diamond is cut too deep, light passes through the side of the
diamond, in both cases inhibiting maximum brilliance.
Take a few moments to read
through this page to become familiar with the various popular cuts of diamonds
used in today's finest jewelry.
The most common, and
the most "brilliant", diamond cut is the Brilliant Cut, a.k.a. Round Cut,
American Ideal Cut, or American Standard Cut.
This design is optically the most efficient, but larger stones (3+
Carats) sometimes look "too big" to some tastes and another cut is preferred.
The Marquise looks
something like a football when viewed straight down from the top. It is
important to note that with the Marquise and other "fancy" cut stones,
you'll want to keep the color quality higher as poor color quality will
show much faster than in round cut stones.
The Oval cut diamond has
an elliptical shape when viewed from above. A well cut oval can be nearly
as bright as a well cut round brilliant shape. Trust your eye to judge
the cut of an oval in natural light. It if looks lifeless in the natural
light it is a poorly cut stone. (Do not be fooled by the dozens of recessed
halogen lights in the retail stores.)
Looks like a rectangle
from the top, with truncated corners. Color plays a very big role in an
emerald cut stone so stay above a 'G' color rating when looking at stones
with this cut.
The pear is a popular
cut that looks like a tear drop. It is often the preferred cut for pendants
and earrings.
Colors tend to play dramatically with the pear cut, as they do in most
fancy cut stones, so stay with the higher color quality when selecting
a pear cut diamond.
The Trillion Cut
is a three sided cut (looking very much like a triangle) but with slightly
bowed sides. Many of these types of cuts are trademarked cuts. The fire
and beauty of the Trillion cuts make this a spectacular cut of diamond.
There are many variations
to the cuts listed above, some are subtle variations and others are extreme.
Small rectangular cut diamonds, which look like small rectangular tapered
boxes are called baguettes. These have much the same facets of an emerald
cut stone but in a much more modern look.