Being a Cut Above

This article outlines the basic steps needed to cut a diamond – a round brilliant cut diamond. It is a process that requires skill, experience and time.

A Cut Above

When a diamond cutter first examines a diamond, the stone is analyzed to decide what shape to obtain. Most diamond crystals are of a shape that makes cutting a round brilliant cut easiest. Some, on the other hand, are such that a longer shape is best – like a marquise cut.

Today, there are instruments that assist in the decision making process. These instruments can provide all the information for maximizing weight retention and still achieving a well cut diamond – even an ideal cut.

The cutter will mark the crystal – or even a broken or chipped diamond needing repair – for the sawing step. He then prepares the diamond crystal by adding it to a special metal stick called a dop. The cement is such that it can be dissolved by submersion in water. Although we will present the steps for cleaving a diamond, we saw them.

Striking a Diamond

Until the advent of the diamond saw, cleaving was the normal way of pre-forming a diamond crystal in preparation for faceting. Cleaving is always in the direction of the diamond’s cleavage. A diamond has grain – directions of parting. If you were, to use a metaphor, to rip a telephone book in half, it would take some serious strength. On the other hand, you can merely part in between the pages to accomplish the same thing. The direction used to part the pages would be the cleavage.

Planes of cleavage follow the original crystal faces. Since diamonds most often come in what is an octahedron – a four sided pyramid on top of an inverted four sided pyramid – there are four directions of cleavage in diamonds. The cleaver, as the person who cleaves a diamond is called, will study the diamond and locate a plane of cleavage. The cleaver glues the diamond in the end of a special stick with cleaver cement (basically shellac and resin with dust from a brick or finely ground glass).

A second diamond – most likely a chip – is cemented to another stick. This is used to make a notch – called a kerf in cutter’s parlance – by rubbing it against the other diamond’s edge. A steel knife-like blade’s edge is then placed in the kerf – steadying the diamond against a bench or in a cleaver’s box. A tap on the blade and the diamond will split.

Sawing Ds

Diamonds are sawn in most cases. Sawing must follow the grain and a small kerf is applied to help align the saw blade. Saw blades are made from bronze and impregnated with diamond powder. The blade is very thin and can be flexed with a light touch. The saw is a machine that rotates the blade in a downward direction against the diamond – which is mounted in a dop. A large brass weight is built into the saw arm to apply pressure to the diamond. The sawyer, as the person who does the sawing is called, watches after a bank of saws – closely examining them to ensure they are not in need of adjustment.

Let There be Light

Lasers have become the modern way to shape diamonds. In fact, a diamond can be cut entirely using lasers. The finish is not as nice as when a craftsperson polishes the diamond but for the most part, laser-cut diamonds can achieve some shapes that are impossible with standard cutting techniques.

Et tu, Brute?

Bruting is the process of grinding two diamonds against each other in order to make them round.

The process involves using one diamond to round up a gem quality diamond. The bruter, as the expert is called that bruts diamonds, does this on a special lathe. One diamond is mounted on a dop – a stick used to hold a stone – and placed in the chuck of the bruting machine. Another diamond, usually but not always industrial quality, is also mounted on a dop. The bruter can hold this second dop under his arm to steady it and use it to round up the gem quality diamond.

Modern diamond cutting techniques employ the use of an automated bruting machine – this is what we use to brute diamonds. Instead of a bruter – the machine has two spinning diamonds that are drawn against each other slowly to round them up.

What a Grind

The wheel used to grind diamonds is a cast iron disc about 12 inches in diameter that turns at approximately 2500 rpm. The wheel is called a scaife.

This true running wheel must be dressed before any cutting can be done. Diamond dust in oil is applied and burned off until the wheel has varying areas of grit. An area exists for determining the proper starting point of a facet. Another area, called the running area, is used to grind facets to their final size. Lastly, an area used for polishing is created for smoothing the facets and eventually polishing them. In some factories, a second wheel is set-up just for polishing as is the case in our factory. This reduces the chance of contamination that may ruin the polish steps.

The diamond powder will turn black. Since diamond is carbon, when it burns it will become black – like soot.

Since diamond is the hardest substance known, nothing will cut, grind or polish a diamond except another diamond. Diamonds have a grain – like wood – with different directions of hardness. The diamond dust, therefore, has particles that will be orientated in their softest direction and others in their hardest direction. Those orientated in the hardest direction can grind and polish the diamond being fashioned into a gem. This diamond also has grain and if not orientated in its softest direction, it will not be affected by the diamond particles, regardless of their orientation. The cutter must examine and adjust the direction of the diamond being ground. A combination of the sound and examination alerts the cutter of where the direction of grain is.

The diamond is held in what is called a tang. This appears like an arm with a multi-fingered vice to hold the diamond. There are raised rods of steel on the bench area to help steady and hold the tang from drifting with the wheel. Sometimes a lead brick is placed on the tang to add pressure on it.

The cutter removes the tang often and examines it to make adjustments, check the progress and prevent burning – the tang is “read.”

The cutting process is not merely grinding and polishing but also includes two other steps, called cross-cutting and brillianteering.

He’s a Cross-Cutter

A cross-cutter adds the first eighteen facets – the table, culet, four corners and four bezel facets on the crown and pavilion for a total of eight bezel facets on the top and eight more on the bottom.

The most important facet in cutting a diamond is the table. The table is the large top facet in the center of the diamond. All the facets are dependent on the table for their symmetry.

After the table is fashioned, the cross-cutter will add the four top facets – on the crown as the top half of the diamond is called. When these are cut, four bottom facets are added and they must align perfectly with the top four facets. The bottom four facets must meet exactly in the bottom center – a center that also exactly aligns with the middle of the table. By the way, the bottom half of the diamond is called the pavilion. Four more facets are added to the top (crown) – thus reaching a total of eight. All eight top facets must be perfectly aligned and the same size. The result is a table that now has eight sides – a perfect octagon.

The cross-cutter now adds four more facets to the bottom (pavilion).

The diamond may be re-bruted – a step called rondisting. This is to make the diamond perfectly round.

The cross-cutter now polishes each facet using the outer area of the wheel.

Sometimes a small facet, hardly noticeable, is added to the bottom tip of the diamond – called a culet. Even though a diamond may not have a culet, called a closed culet, it is nevertheless traditional to call even a pointed bottom’s point the culet.

A Brilliant Step

Once the cross-cutter has completed his grinding and polishing steps to satisfaction, the diamond is turned over to the brillianteer. The final stage of cutting is handled by this operation. There are twenty-four facets left to be added to the crown as well as sixteen on the pavilion in order to make a round brilliant cut diamond.

The first facets to be fashioned are the eight star facets – small triangle shaped facets that surround the table – to create an eight pointed star.

Next, sixteen upper girdle facets (as gemologists call them) – also called the halves (as cutters call them) are added to connect the star facets to the girdle. The girdle is the term for the diameter area between the crown and the pavilion. The original facets added by the cross-cutter will become kite shaped (they are called the kite facets by cutters) and are called by gemologists the upper bezel facets.

The brillianteer now adds the final bottom facets to the diamond. These are the sixteen halves or bottom girdle facets – depending on whether you are a cutter or a gemologist.