Diamond, gemstones, precious stones

Bear in mind also that a good diamond cutter can cut a colored stone in order
to make it appear whiter than it is WHEN THE STONE IS MOUNTED by doing a
shallower cut that’s more spread on the point where the facets come together.
This will make the stone appear less yellow, again only after it’s mounted.
This is another reason one should never judge a stone that is in a mounting
of any sort.
The cut of a brilliant diamond may be the most singular important consideration
in buying a stone within a set price range. Unless one is an expert and feels
his knowledge is good enough to override general public consideration, there
is only one cut to consider and that is the “brilliant” cut. Brilliant cut is
a modern cut that is a completely round stone designed with 58 facets to
maximize light reflection and “fire” within a diamond.
There are a lot of stones still around which have what is known as a European
cut. This cut was done in the 1920′s and before and does not compare in value
to the modern brilliant cut. The old cut or European cut stones were cut
before exact ratios and angles were established and understood by the gem
cutting society and, as such, do not maximize the reflecting and refraction
qualities of the stone. European cut stones such as those purchased at pawn
shops and estate sales, are much harder to resell and do not offer the
liquidity of a brilliant cut diamond.
There are other popular modern cuts such as the marquise, the oval and the
pear which attract some buyers when designed for jewelry, due to their unique
appearance. These cuts do not reflect as well as the brilliant cut and are
rarely seen in investment quality jewelry. Again, the fancier cuts will be
on the average much harder to sell (definitely harder to sell to a dealer)
than is the round brilliant cut stone.
Fancy cut diamonds have fewer angles cut to what is known as the “critical
angle” and, as such, cannot be as brilliant as a round cut stone. The fancier
a stone is, the more it differs from a brilliant cut, the greater the loss in
light reflection will be.
Another phenomena to be aware of in fancy cut stones such as pear shapes or
marquise shapes, is something called the bow tie effect. This is a dark,
cloudy area across the upper portion of the table on these stones. It is a
quality inherent in the cutting and looks like a cloudy bow tie across the
reflecting portion of the table. This obviously lowers the value of the stone
considerably and, if one is thinking about a fancy cut stone, this effect
should be taken into consideration.
Fancy cut stones have only two bottom facets as opposed to the eight found in
round cut stones to reflect the light back. While they still may appear to be
fairly brilliant, the refraction, the fire of the stone, will suffer
critically. This loss progresses from the marquise cut through the straight
cuts such as the emerald cut diamond. These straight cut stones suffer a great
light and fire loss and are not nearly as valuable as the same stone would be
cut in a brilliant cut.
An uncut diamond is normally sawn or split into two or more stones as decided
by the diamond cutter. It just takes a simple error here to completely ruin a
valuable stone and turn it into nothing but dust. Now you can understand the
hypertension rate among diamond cutters and airport controllers…
Once a rough diamond is split, the diamond cutter then decides how the stone
will be laid out and cut. This operation means that a certain portion of the
diamond will be ground off and lost and so this cut plan becomes an important
step in finishing the final stone.
The first step taken by the diamond cutter is to girdle the diamond. This
process of girdling establishes the size of the stone and puts a “waste” on
the stone (see the diagram). If a stone is poorly girdled, it will not appear
completely round when viewed with the jeweler’s loupe or microscope. A round
brilliant cut stone should be perfectly round and symmetrical.
Other mistakes in girdling will produce flaws that manifest themselves as a
razor thin girdle which is prone to chipping or breaking (even though diamonds
are extremely hard, they are brittle and can be chipped or shattered in thin
areas). A too thick girdle takes away from the brilliance and fire of a stone
and indicates a poor job on the part of the diamond cutter.
A diamond cutter cuts (in a brilliant cut) 58 facets all done on exact angles
in exact positions in order to let the diamond reflect as much light as is
physically possible. The brilliant cut stone has 16 facets on top and 16
facets on the bottom that reflect the light and give the stone its cut. Each
facet is cut on a unique angle and is exactly straight when viewed with other
facets in order to maximize light reflection.
When you view a brilliant cut stone, around the table of the stone you’ll see
the kite and the topmain facets. These facets are the areas that allow the
light to come through to the viewer. Beneath these you have eight star facets
and then 16 upper girdle facets before you reach the girdle itself. Beneath
the girdle you have an additional 16 lower girdle facets. All these ancillary
facets contribute to the light reflection through the kite and top main facets
and the table portion of the stone.
What is the advantage of the 58 facet brilliant cut stone? What does one
expect to see when viewing a diamond? There are two qualities that make a
diamond attractive to the eye. The first one is known as life and indicates
the amount of light that is reflected back from the diamond to the viewer.
The second quality is known as fire, which is an indication of the amount of
refraction from the facets and split into colors as in a prism effect.
Besides the 58 facets, a number of other factors contribute to the perfectness
of a brilliant cut stone. The stone’s table should be 53% of the area of the
stone. While the ratio between the depth of the stone or the length of the
stone if you view it from the side, to the spread of the stone which is the
maximum diameter of the girdle, this ratio should be 60% depth to spread.
The angles on a stone must be cut exactly to critical angles. Any deviation
will produce a less than perfect reflection of the light waves entering the
stone. A jeweler will have special gauges to measure these angles. These
gauges are available but they are expensive. Or one can buy a loupe that is
marked with angle markings.
When angles are viewed through this loupe, they can be accurately measured .
The first measurement to take is the degree of the angle from the table to the
girdle of the stone. This is known as the top critical angle and should be 34
1/2 degrees. Underneath the girdle, the bottom angle from the girdle to the
point of the stone is also a critical angle and should be cut at 40 3/4
degrees. A further measurement is that the girdle should be about 1% as thick
as the diameter of the stone, although this is not quite as critical as the
other measurements and can be judged by the eye after a bit of practice.
A stone which is not cut with the critical angles in the right degree, will
either be shallow cut or deep cut and will not reflect the light back through
the center of the stone (the table of the stone) with the same brilliance as
a stone that is cut to the correct angles.
If the stone is shallow cut, the light will reflect off the edges of the stone
but not through the middle. If it is cut too deeply, the center of the stone
will appear to be dark and it is called “heavy.” In the past some cutters cut
the upper angles at a less than 30 degree cut. This “spread cut” helps hide
deficiencies in a stone but makes the girdle angles sharp and likely to be
broken or chipped and the stone is not as valuable as a normally cut stone.
If the correct tool for sizing angles is not available, one can estimate that
if the table appears to be larger than it should, and the width to height
(that is the depth spread ratio) is below 60%, one can assume that the
critical crown angles are shallow.
It is possible to polish a diamond to a high degree to compensate for shallow
or deep cut angles at first glance and make the stone appear to be more
brilliant than it, in fact, is. If the stone is chosen for investment quality,
a measurement of these angles is almost essential .