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!