Diamonds are the hardest mineral on earth, and it’s no small miracle that they can be shaped to an exacting degree such as those found in faceted gemstones. But many of us have wondered over the years exactly how these stones can be cut when, at the end of the day, they actually define the top level of mineral hardness.
So, if you’ve ever wondered how diamonds are cut, you’re in the right place. Read on and I’ll explain how the process works.
Can You Really Only Cut Diamonds With Other Diamonds?
It turns out that in order to cut diamonds… you actually need diamond dust in the first place. The most common abrasive used for cutting gems is corundum, or aluminum oxide. It’s even used in sandpaper. The problem is that a diamond will simply wear down the grains of this material.
Fortunately, diamonds are very, very hard but also brittle. While you won’t scratch a diamond with anything but another diamond, they’re easily smashed with a hammer or other crushing device.
Don’t worry, these diamonds are generally considered industrial grade. That means they wouldn’t be fit for jewelry due to inclusions and other problems.
These are used in various parts of the diamond cutting and polishing process. Diamond impregnated tools are fairly common due to the wide availability of these inferior diamonds. They’re often used by lapidaries for cutting and carving stones, although diamond grinding wheels are a bit less common.
But in the end, without this powder you’re not going to be able to do anything to a diamond but smash it.
The Cutting Process: Start to Finish
Cutting diamonds is more intensive than cutting other stones. Even sapphires, with a hardness of 9, are cut like “normal” gemstones.
The high value of diamonds also means that there are a lot of factors that may not come into play with other stones. So, let’s start at the beginning.
Planning the Cut
Quite often, diamonds of any significant size are first scanned into a CAD program. This program allows the cutter to view the diamond in three dimensions, rotating it as needed. They’ll then identify the cleavage planes of the diamond.
Some programs will automatically identify the ideal cut for the stone, as well as whether or not the stone needs “sawing.” The basic idea here is to get the most out of the diamond that they can, maximizing the value of the stone.
Remember, two of the “Four Cs” of diamonds are carat and cut.
The following factors are all taken into account during the planning process:
- Weight Retention- The carat size of the diamond is incredibly important to the value. In some cases it’s more valuable than the cut itself. Most diamond planning is done with retaining the most weight possible in mind.
- Inclusions- Diamonds are commonly included, and the basic idea is to minimize their appearance in the stone. The stone can be planned to be cut with inclusions removed, or in such a way that they’re less visible to the naked eye.
- Color Retention- Diamonds can be cut in a way to accentuate the color, depending on the cut, depth, and other factors. Some colors are only on the surface, so planning involves keeping as much of the natural facing of the stone as possible.
- Turnaround Time- Some intricate cuts are worth far more than the average round brilliant, but they may take longer to sell. Diamond cutting is still a business, so only exceptional stones generally receive fancier cuts.
From there, the cutter will proceed to either sawing/cleaving or just begin round the stone to the proper domed shape to begin the faceting process.
Cleaving or Sawing the Diamond
Most rough diamonds have natural planes of cleavage, which need to be sorted out to prevent a weak point in the finished stone.
Sawing a stone with cleavage involves cutting a small groove that is along the right plane, and then striking the groove with a tiny steel chisel-like tool. This causes the diamond to break along the proper plane and is referred to as cleaving.
This is obviously a delicate task.
Sawing is used when the stone doesn’t have any natural cleavage planes. In the past this was generally done with a diamond bladed saw similar to a hacksaw or jeweler’s saw with impregnated diamon dust.
Currently, it’s often done with a laser. A laser will have a finer kerf (the area of removed material) than even the smallest saw blades and is more precise than working a saw by hand.
Rounding the Diamond
Now, the face of the stone to be faceted needs to be rounded.
This can be done in a few ways.
In shops with access to them, lasers are often used for this part of the process. This is faster and also allows for a more even dome than one which is created with other methods. Not every shop has access to the correct laser for this process, however.
The oldest method was the scaif. This was a horizontally spinning disc that was coated with diamond dust. Eventually it evolved into something similar to the modern flat lap or faceting machine, and this method is still used as well.
The most common method is called bruting. After rough shaping on a faceting machine using diamond as an abrasive, two diamonds are put into a special machine. It resembles an extremely high speed lathe with a slight offset.
Once affixed, the machine is adjusted and the diamonds are spun against each other, allowing for the creation of a round brilliant diamond which is perfectly rounded around the center of where it was held.
The use of a faceting machine is required for any shape other than round brilliant diamonds, which is why these are always more expensive than a similarly graded round diamond.
Creating and Polishing the Facets
With the rough shaping of the diamond done, the individual facets must now be created and polished. Prior to the invention of the scaif, the true brilliance of diamonds wasn’t really known. Older cuts simply failed to enhance the optical qualities of the diamond.
These are done at a precise angle, with special attention paid to symmetry. All diamonds are faceted to some degree, although round brilliant cuts are the most common.
The exact arrangement of facets varies, but the process for a round brilliant is well known:
- The eight pavilion facets are cut first. These are the facets on the underside of the diamond. These are cut in specific directions due to the way diamond’s molecular structure is formed.
- The crown is then cut. These are the facets at the top of the stone, centering around the table. The table is the flat bit at the top of a faceted stone.
- The bruting of the diamond is checked. It must be rounded to within 1/10th of a millimeter in order to be considered an “excellent” cut during appraisal.
- These 16 facets are then polished using a higher grit than that used to grind them during the initial creation of the stone’s shape. This results in a round.
- The next stage is known as brillianteering and is the crucial difference from older rounds. Further cuts are placed on the stone, including 8 more on the upper portion of the crown(“star cuts”), 16 more on the crown(“crown halves”), and 16 more on the pavilion (“lower girdle”).
- The cut is looked over a final time before passing into quality control. Emphasis is on symmetry and the angles of the cut, since the ideal angles give the best “fire” in the diamond.
The cut diamond is often washed in acid to remove anything left on the surface. It’s then examined for a final time before being sent off for proper grading. Fancy cuts will vary from the above process, but the essentials are the same. The diamond’s facets are added gradually until the final form is achieved.
Diamonds are graded on color, cut, carat weight, and clarity.
Cut is often considered among the least important qualities as long as it’s not terrible. That said, there are very specific guidelines for round brilliant diamonds involving angles and roundness. Round brilliant diamonds are the only ones which are specifically graded by gemological labs.
Most diamond businesses will assign their own grade for fancy cuts, depending on symmetry, polish, and brilliance.
