Diamond Jewelry King » Brilliant cut

Polishing diamonds

King of diam — Sun, 20 Sep 2009 10:21:07 +0000

The polishing mill is an extremely simple machine, consisting of a circular horizontal plate of cast iron 14 or 15 inches in diameter, (called a skive,) suspended on a spindle, and capable of being put into rapid motion by means of a larger wheel 5 or 6 feet in diameter, and turned by an assistant.

From the centre to the circumference of the iron plate are lines or shallow grooves formed by rubbing it in that direction with a fine-grained gritstone; these grooves serve to retain the mixture of oil and Diamond powder with which the plate is charged. In order to keep the Diamond perfectly steady while the polishing of each facet is going on, the following contrivance is had recourse to. A copper cup (called a dopp) about three quarters of an inch in depth and in width, and furnished with a stem about four inches long of stout copper wire, is filled with plumbers’ solder, which also projects in a conical form beyond the rim of the cup: in the apex of this cone, the solder being softened by heat, the Diamond is imbedded with one of the facets projecting.

The stem of the cup is now put into very powerful pincers, which screw up with a nut and a wrench or lever, and thus hold it perfectly tight. The handles of the pincers (called tongs) are of wood, are broad and terminated by two feet, about an inch high, so that when laid horizontally they are supported exactly as a pair of candle snuffers is, the studs fixed to the handles of the snuffers representing the legs of the pincers, and the single stud near the point of the snuffers representing the inverted copper cup holding the Diamond, and at the same time having its stem strongly griped by the pincers. In this position the Diamond is placed on the plate, the pincers resting on their legs on the wooden bench or table that supports the plate, and pressing at the same time against an upright iron peg; the broad part of the pincers between the legs and the Diamond, is then loaded with weights, both to steady the machine, and to increase the pressure of the Diamond against the skive.

Matters being thus adjusted, a little oil and Diamond powder is dropped on the plate, it is set in motion at the rate of about 200 revolutions in a minute, and the process of grinding down, and at the same time of polishing is begun. The Diamond is taken up and examined from time to time, and is adjusted so as to give the facet its true form. The heat occasioned by the friction is at all times pretty considerable, and when the pincers are heavily loaclen it occasionally increases to such a degree as to soften the solder and displace the Diamond. This is a serious accident, frequently occasioning a flaw in the Diamond, and always tearing up the surface of the skive so as to damage it very considerably. There is room on the skive for three or four Diamonds at the same time; and to give each its proper share of attention is as much as one person can well manage. The completion of a single facet often occupies some hours.

Diamonds are brilliant cut, rose cut, and table cut. The brilliant is deservedly in the highest estimation, as it is the form which shows to the greatest advantage the peculiar lustre of this gem. The proportions and method of forming the brilliant are described by Jeffries; and with regard to the shape and position of the facets no change has hitherto taken place, although, from the present fashion of preserving as great a spread or surface as possible, the rules for proportioning the dimensions of the brilliant are by no means strictly adhered to.

The brilliant may be considered as formed of two truncated pyramids united together by one common base, the upper pyramid being much more deeply truncated than the lower one. The plane formed by the truncature of the upper pyramid is called the table (a); that formed by the truncature of the lower is called the collet (b); the common base is called the girdle (c); the space between the table and the girdle is the bizel (d) and that between the girdle and the collet is the collet-side (e).

Both the table and the collet are regular octagons; the bizel is formed by eight lozenges and twenty-four triangles; the collet side is occupied by four irregular pentagons alternating with as many irregular lozenges, radiating from the collet as a centre, and usually called the pavilion facets, and bordered by sixteen triangular facets, adjoining the girdle. The brilliant is set with the table side upwards, and the collet side implanted in the cavity made to receive the Diamond.

The regular rose Diamond, is the form given to those stones the spread of which is too great in proportion to their depth to admit of being brilliant cut, without a great loss of substance. It is formed by covering the whole surface of the stone with equilateral triangles, each pair being placed base to base, so as to form a kind of rhomb.

The table Diamond is the least beautiful mode of cutting, and is applied only to those stones or rather fragments, which with a considerable breadth have only a very trifling depth.

Good stones, from one to four or five carats, if skilfully cut either into brilliants or rose Diamonds, lose in the process somewhat less than half their weight; hence the value of a cut stone is twice that of a rough stone of equal weight, independently of the cost of cutting.

The Diamond-cutters of England are confessedly the best in Europe, but their number is unfortunately so small as to, occasion many stones to be sent to Holland ; where, from the greater number and more active competition of the artists, the price of workmanship is considerably lower, but in at least an equal degree inferior to that of London. Brilliant cut Diamonds are so infinitely superior to the others, that of late many rose-cut stones from Holland have been recut into brilliants, notwithstanding the additional expence and the loss of size necessarily attendant on this operation.

Diamonds themselves are always equally in fashion, but the mode of setting them varies according to the caprice of taste or the desire of novelty : hence the jeweller has perpetual opportunities of exercising and displaying the inventive elegance of his taste in the assortment of hues and the arrangement of groups. He will cluster together the smaller stones so as to aggrandize and enhance the effect of the whole; the larger and more perfect ones will generally be set open and displayed to the greatest advantage, while the inferior ones will be assisted by setting them solid on black, or, if need be, with coloured foil.

But whatever be the occasion that calls forth his art, whether the construction of a star, a bandeau, a tiara, a plume, a necklace, or an ear-drop, he will bear in mind that his greatest merit is the concealment of his art: the display of belts and borders of gold can add nothing to the superlative splendour of the Diamond.

Silver fades in the presence of gold, gold itself yields to the more brilliant and costly materials of the jeweller, and of these the most beautiful, the most costly, the very perfection of the gem creation is a colourless brilliant without speck or flaw, large enough to attract notice, yet not so bulky as to be cumbersome in itself, or too disproportionate to the smaller ones with which it is associated.

Cut grading diamond

King of diam — Sat, 19 Sep 2009 22:15:55 +0000

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 .