Mad About Science: Lapidary arts

By Brenden Bobby
Reader Columnist

I first learned about the Mohs scale in elementary school — a simplified, tiered ranking of various minerals ranging in hardness, each one able to scratch the one beneath it. For whatever reason, this was a particularly fascinating revelation for my class. 

Perhaps being given clear instruction on what is best and worst at performing a task — and trying to disprove this universal truth was — a conundrum that spoke to young and curious minds. It made me ponder the world around me. If diamonds were unbreakable, how did we have faceted jewelry? Why aren’t vehicles and buildings just made from diamond?

It turns out that even the universe’s rules are made to be exploited and broken.

Lapidary is a practice of manipulating gemstones to create jewelry and other items, often for aesthetic purposes but sometimes for functional ones as well.

Creating a piece of jewelry calls on many different professions to deliver a final product. We’ll focus less on the work of a goldsmith and more on what a lapidarist, a gem cutter, does. While these are different expertises with different tools, sometimes a jeweler will have access to everything and be able to assemble an entire piece of jewelry in-house.

Gemstones aren’t faceted or even polished in their default state. A raw diamond often looks like a very rough ice cube and, to the untrained eye, likely just looks like a rock. This is just as true now as it was thousands of years ago when humans first started working with gemstones. We don’t have a very clear timeline on when humans first started working with precious gems, though the entire process is very closely related to the knapping process we explored in the June 29 edition of the Reader about arrows.

At some point in our distant past, neolithic humans discovered that certain rocks were harder than others and possessed the capability to carve chunks from other stones. It’s likely that some of the first stones used by humans for knapping were obsidian, which sits at a 5 on the Mohs scale.

Surprisingly, silicon, formed into glass, was also another commonly used tool for carving around 2000 BCE. Glass is extremely brittle, but it has an exceptional ability for cutting and scratching other materials. Sitting at a 6.5 on the Mohs scale, silicon is well-suited for grinding, scratching and even carving softer materials. Sandpaper is commonly used in lapidary to grind and polish gemstones.

Humans used stones to carve other stones directly for thousands of years. It wasn’t until relatively recently that we began using more advanced tools and marrying stone with metal to achieve incredible results. Most contemporary lapidary is performed with metal tools using diamond blades. 

Though you may be envisioning a glittering, semi-transparent saw blade made of pure diamond, this is not actually the case. The blades are steel, but they have been embedded with tiny bits of rough diamond that work like sandpaper to generate heat from friction, which allows for manipulation of other stones. Motorized tools give us precise control of large amounts of energy to apply to a surface that our ancestors could only dream of. While pedal-powered machines may have been used, they could hardly compare to an electric-powered saw.

Diamond blades need to have a relatively uniform dispersal of diamonds throughout the structure. This can be hard to achieve with traditional forging techniques, and instead other disciplines are often used to create diamond blades. Electroplating is common, using electrolysis, which is a process whereby an electrical current is run through structures in a liquid bath to attract a uniform coating of a desired material. Electroplating gold and copper onto jewelry is a common practice, and has been for a very long time — even before the discovery of electricity — with the help of various chemicals found throughout history.

Enough about that, though; how does someone go about cutting their own gem?

This is done in a number of stages, beginning with planning. As with virtually everything else in our lives, it begins with a computer. Using specialized CAD programs, a lapidarist can calculate the optimal size and shape of a finished gem from a rough stone, which minimizes the amount of material lost and retains the maximum weight. In some cases, gems are cut to enhance their natural colors, rather than for their weight.

If a large amount of material needs to be removed from the gem, or if two gems are coming from one rough stone, it must be cleaved. This is often done with the combination of a laser and a diamond blade saw. A cleavage plane is identified, where the atomic bond is at its weakest and most susceptible to breaking, and the laser is used to create a groove, which is then exploited by a saw to cut it along a specified plane and make the piece easier to work with.

The lapidarist will mount the stone to a machine using a jeweler’s putty that hardens at room temperature, but melts when heat is applied. This keeps the gem in place when forces are applied, but makes it easy for people to manipulate as need be.

The machine is a specialized planing grinder with a downward-facing mast the gem is attached to. The cutter will grind a face of the gem to their desired level, then rotate it by a set amount, usually 45 degrees to create a gem with eight sides. This portion of the process is called blocking, and is similar to blocking out rough shapes of a sketch on a piece of paper.

Creating the extra facets along the top of a gem and polishing them is done by two different people, using a very similar process on a smaller scale. This is the portion where the gem is most likely to be ruined, as even tiny imperfections may destroy the value of the gem. 

A “brillianteer” — the person in charge of polishing — uses extremely fine-grain materials to polish the stone. Sanding materials are graded by the size of their grit, and while you may have used anywhere from 40 to 1,500 ultrafine sandpaper, this process is usually done by materials with a 50,000-grade grit, which is microscopic.

Stay curious, 7B.