cutting concave faceted gemstones Ashton Gems, California

I was 12 years old in 1970 when I attended my first lapidary class with my grandmother. We entered a giant warehouse full of rows of grinding machines, saws of all sizes and a separate room full of faceting machines. I didn't have a clue of what I was looking at or how it would change the direction that my life was going to go.
For the next two years, on Tuesday and Thursday nights, I learned how to operate the grinders and use all the different sanding and polishing wheels. For the first few weeks, I

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just stood and watched my grandmother and her friends grind and polish what looked to me to be pieces of gravel, but once finished were beautiful Jade, Agate, or Opal cabochons.
Over that two-year period, I learned a lot about rocks, cutting and polishing, rock shows, and where in the U.S.A to find different stones and minerals. But there was one thing that fascinated me that I could never get out of my head and that was standing in the room where the faceters were cutting. How could they take a tiny little chunk of rock and turn it into a gemstone? They did this like they weren't even thinking about it, having a great time, talking to each other, running the stone back and forth on the disc, taking a peek at it now and then. Truly, these guys were the masters of the world.
How could I become one, too? In 1972, I bought my own equipment, and did my cab cutting at home. That lasted until 1975, and I really didn't have time to cut anymore. Besides, how many belt buckles and bolo's can one person make?
Fast forward to 1990. The memories of those men faceting never left my mind. I took my kids to a local rock show so they could see the exhibits, equipment, and the finished stones for sale. As we walked through the exhibition hall, we came across a sales rep. for Graves Faceting Machines. This was my chance to become a faceter. I bought the Graves machine and used it for about 17 years. It was a good machine for someone just starting out, or only cutting now and then. But if you are a serious cutter who wants perfect flat facets, the older Graves machine was just not consistent enough (at least not for me).
So let me introduce our company, Ashton Gems, which is located in Northern California in the Sonoma Wine Country (that's about 64km north of San Francisco). My wife, Morgan Mattos, is the CEO and CFO, and I'm the employee who does the gem cutting and empties the trash. Morgan also works full time for the Superior Court. My name is Larry Mattos, and I am a retired custom tile setter and police officer, although I still instruct at the police academy part-time. The name of the business, as well as the names of many of our gemstone cuts, are based on characters and places from the book, "The Guernsey Literary and Potato Peel Pie Society." This is in honor of Morgan's mother, Mary Ann Shaffer, who wrote the book with Morgan's cousin, Annie Barrows. The overwhelming success of their book afforded us the opportunity to take my love of gem cutting from a hobby to a business.
We specialize in cutting concave and fantasy cut gemstones. From what I have been told, cutting concave faceted gemstones is basically nonexistent in England. If this is true, let me show you faceters what you are missing.

I believe that the Ultra Tec Faceting Machine is the finest in the world. So, in 2008, I took a drive to Southern California (about eight hours each way) to their headquarters. I was given a tour of the facility, and I have to say, this is a very interesting company. I was shown how all the parts of an Ultra Tec machine were made, assembled, and tested. What is unique about Ultra Tec is that almost every piece of their faceting machine is made in one location. Very few parts are made by anyone else and none are cast aluminum -- they are all milled from stock. The price of the Ultra Tec machine is fairly steep, but after you cut a few stones, you'll see it's worth every penny.

The first Ultra Tec Faceting Machines were introduced in the 1980's, if you bought a machine back then and want to update it, the design is still the same and any new features will fit.

In 2010, Ultra Tec introduced the Concave Faceting Machine and the Fantasy Machine. This is taking faceting to a whole new level. Fantasy and Concave Cuts can be made on any gemstone. These unique cuts involve the creative use of refracted light through a gemstone to form unusual effects. Refraction, or the reflection of light as it travels through a gem, can be greatly increased by adding more surfaces (facets). As the gem cutter adds grooves or concave facets in the stone, the light reflects back in entirely new ways. This results in designs not possible using traditional cutting techniques--pieces that are truly distinctive-- with no two exactly alike. Another key benefit of Fantasy and Concave Cutting is that it can increase a gem's brilliance by 5-7 times.

In the photo of Morgan's Star, the stone on the left was cut on a regular faceting machine. The middle is a side view of the same cut with three small concaves in the sides (using the mandrel tool). The stone on the right is the finished concave work. These were both cut from the same piece of Citrine, although the concaving makes the stone much brighter.

On the Fantasy Machine motor, there are two motion elements-there is the Tool Drive that provides tool rotation, and there is the Table Drive that provides tool reciprocation (which is adjustable). The motor table plate moves left or right from center, this can be controlled by a dial indicator. The table will also pivot left or right, using a protractor for exact placement. Depending on what tool you are using, the motor can be removed from the plate and remounted at 90°.

Tools that come with the Fantasy Machine are:

1) Slice Tool - puts small slices in a flat facet
2) Round Ball Tool - puts a dimple in a facet and changes where the light goes inside the stone
3) Mandrel - puts concave grooves at any depth or width you like
4) Polishing Tools - comes with wood (maple) tools the same sizes of the cutting tools, these work very good and fast with any of the oxide polishes or diamond.
5) An adaptor for small carving tools.

You will notice in the tool photo, the cutting surface of the tools is copper and you might think that this is too soft to cut stones. The diamond paste that is put on the tool does the cutting not the copper.

With your gemstone on the mast, set the angle you want to cut at. Like any other faceting machine, install the tool you want to use and cover with a thin film of diamond paste (I like using 1200 paste, it cuts fast but doesn't leave scratches that are hard to polish out). Lower the gem down slowly onto the tool. Example: You could cut the pavilion of a round brilliant and put a small slice in each main facet, or maybe put a dimple in each one, the optics in the finished stone are incredible.

When I do a concave cut, I start by cutting my pavilion from start to finish (including polishing) on my regular faceting machine. I then transfer the dop stick over to the Fantasy Machine and cut with the tool I'm going to use. Polishing after will depend on what kind of effect you want, most stones I don't polish.

After you have done all the concave or fantasy work, the dop stick is then put in the transfer jig and reversed for cutting the crown. The photos that I have included in this article have not had any concave work done on the crown, though it is commonly done.
Hopefully, there will be an opportunity in a future issue to show you step-by-step instructions on how to cut a concave gemstone.
Please visit our website at, and you will find more photos and cutting diagrams that can be downloaded at no charge. If you have any questions on concave/fantasy cuts, cutting diagrams, or purchasing Ultra Tec Faceting, Fantasy or Concave Machines and tools, you can email us at This email address is being protected from spambots. You need JavaScript enabled to view it. or phone us at (707) 769-1706.
Happy Faceting! Larry Mattos

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