Monday, April 23, 2007

What is meant by "Ideal Cut"?

Great question, you'd think there would be a quick and easy answer. But, no.

The term "ideal" has often been used to describe only the best cut diamonds, but it’s also been confused and abused over the years. After 300 years of experimentation and refinement, experts now agree that there's more than one simple way to describe the cut of a round brilliant diamond.

Although he never used the word "ideal" in his proof of Diamond Design (1919), Marcel Tolkowsky argued that a very tight range of proportions – based on Table Percentage = 53%, Crown Angles = 34.5 degrees, and Pavilion Angles = 40.75 degrees – produces optimal fire and brilliance in a finished gem diamond. Like most basic mathematics and physics, his numbers have withstood the test of time. They still hit the "sweet-spot" of most modern ideal standards.

After teaching 1000’s of gemologists about these “ideal” proportions over many years, the Gemological Institute of America (GIA) did not issue proportion-based cut grades on their diamond reports. However, they did recently introduce a performance-based grading system for cut that defines five levels of cut quality - Excellent, Very Good, Good, Fair, and Poor - with the top two grades being the most prevalent.

For the past decade, the American Gem Society (AGS) has pioneered and strongly endorsed the use of “ideal” in conjunction with a consumer-friendly numeric scale of 0 - 10 (with “0” being Ideal) to quantify multiple factors affecting cutting quality. Their Zero Ideal Cut Grade is based on an overall combination of ideal light performance, ideal proportions, and ideal finish – which includes ideal polish and ideal symmetry. This top grade represents just 3% of round diamonds in the marketplace.

There are diamonds that also exhibit extra “ideals" when viewed in various viewing devices. Some show ideal patterns of optical symmetry when you view diamonds directly under specialized filters and lighting environments. Others generate ideal computer-generated numbers, scales, images and guides that compare one "virtual" diamond with another.

But, diamond reports and viewing devices will only ever tell you so much. In the final analysis, I always recommend looking at any diamond you may consider owning. That’s what all the experts I've ever met do.

Why? Because, diamonds are dynamic 3-D works of art! They express their beauty in motion. Their true nature and appeal is impossible to reveal with a mere snapshot. It should not come as a big surprise to find that they often look very different in reality than they do “on paper”.

Sunday, April 22, 2007

What is diamond cutting?

It’s well known that it takes a diamond to cut another diamond, because diamond is the hardest substance in our world. That is the scientific truth. But, there’s a bit more to it than that.

Generally speaking we think that to cut is to stab, slash, slice or snip. The fact is that diamonds are cut – or as my friend Gabi Tolkowsky would say, fashioned – more like splitting, sawing, lathing, sanding and polishing wood.

Most rough diamond crystals are first split into two “workable” pieces. Traditionally, this was done with a hammer and blade in a process called cleaving. Cleaving is very much like splitting wood along its grain. Diamond can be split along one of its “grains” – parallel to the octahedral face – by placing a blade in a pre-carved notch – called a kerf – and striking it as you would a wedge. Today, however, diamonds are typically sawn in two along a different "grain" - parallel to a cube face - with either a phosphor-bronze diamond-dust encrusted blade or with a pulsing laser beam.

Next, the diamond is shaped. This form of cutting is called bruting, because it is forced against all grains. This is done with the gem diamond centered on an eccentric-chucked lathe. The diamond is then turned round by rubbing it against another diamond-topped cutting tool. Elliptical shapes like oval, pear and marquise are formed the same way by tapping the lathe off-center. Any straight-edged diamond - like emerald cut, square cut, and/or princess - is always shaped on a flat grinding wheel that is charged with diamond dust.

You know the old saying "nose to the grindstone"? Well, where do you think that came from? The final stage of diamond cutting is faceting. All facets on a diamond are ground and polished on a flat cast iron lap or wheel that is shaped like a record turntable and coated with super-fine diamond dust. Each facet is cut by placing it at the correct angle against the wheel with one of the diamond’s twelve grains - dodecahedral faces - held perpendicular to the spinning direction of the wheel. One and only one of these 12 grains will cut well for each facet position.

Having to know the exact location of each grain in a diamond is what separates a diamond cutter from all other stone cutters. Diamond will cut anything else, like butter, but it will only cut another diamond in very particular directions.

Just as with other industries there are varying levels of skill and craftsmanship employed in diamond cutting. The highest degree of skill is in the total hand-crafting and finishing of the stone by a master cutter. The cutter literally feels, sees and judges how well every single facet is cutting. This is cutting the "old-fashioned" way. It definitely yields the most beautiful results. If you ask me, it’s the way all diamonds should be cut.

Of course, there is also an assembly-line method of production which speeds things up and increases the volume of diamonds that can be processed worldwide. This style of cutting has semi-skilled cutters performing single operations over and over again at a high rate of speed while obviously compromising critical aspects of accuracy. There is also a fully automatic method of computerized cutting which is most often used for smaller diamonds. Believe it or not, this characteristically achieves the least consistent and reliable results, mainly because the computer never physically "sees" the work. The entire process is mechanical.

As you might have guessed by now, only the simplest and earliest form of diamond cleaving is actually possible in the back seat of a Mercury. Yet this is the image that most people conjure up when they visualize the diamond cutting process. Such is the power of successful TV advertising from almost 40 years ago!

Friday, April 20, 2007

Basic terminology

Let’s start out with some really simple definitions. We can explore each in more detail later on, but it’s always nice to have a common foundation.

Cut makes a diamond shine. The best cut diamonds are cut for maximum beauty – not for excess weight. They must have the best proportions and finish to maximize the play of light. Their color looks better, their clarity looks better, and they often look larger for their “size”, because the best cut diamonds shine from edge-to-edge with brilliance and fire. And, on top of all that, they sparkle like crazy.

Color is the shade of the diamond itself. This is distinct from the spectral components of light that should radiate from any well cut gem diamond.

Clarity is how clean it is. Most diamonds have natural identifying marks. On very rare occasion they have no inclusions. The value of diamonds is significantly higher for those with nothing visible to the naked eye.

Carat is a weight – not a size! One carat is equal to 1/5th of a gram. One point is 1/100th of a carat. Carats are expressed like money - 1.50 ct. is one carat fifty points or 1 ½ carats. Size is the measurement of the diamond’s diameter in millimeters (mm). Many one carat diamonds measures less than 6.0 mm in diameter. The best cut rounds measure much wider at 6.50+ mm in size.