Journey into the World of Jambpeg Faceting

Justin K Prim
Justin K Prim
Published in
10 min readDec 16, 2023

This article originally appeared in the December 2023 issue of the US Faceters Guild newsletter.

On the verge of my ten-year anniversary, I decided to start all over again with a new machine, a new technique, a new style, a new state of mind, and in a new country. For the past month, I’ve been immersed in the French technique of jambpeg faceting, travelling around France to meet machine manufacturers and cutters, and generally trying to make myself a better lapidary.

I originally started my lapidary adventure in January of 2014 in San Francisco, California. Through the help of the members of the San Francisco Gem and Mineral Society, I learned how to make cabochons, how to carve on cabbing wheels, how to drill, how to free hand facet, and after a year and half of waiting, I learned how to facet using a vintage Ultratec V2. As my cutting abilities blossomed, my faceting journey deepened, taking me to Scotland and London and then Thailand and Sri Lanka. It was in Bangkok that I got the offer to help open a faceting school and which, as a side effect, caused me to switch faceting machine styles.

I first went to Sri Lanka in September of 2017 to learn the art of the Sri Lankan handpiece machine. After a few lessons and a few months of practice back in Bangkok, I fell in love with the machine and its unique faceting style. By then, I had been faceting on American mast machines for two and a half years and had become really comfortable with the machine and the techniques that came with it. Once the cutting school in Bangkok opened, I made the permanent transition to the handpiece machine, causing my Polymetric Scintillator to collect dust in the corner.

Fast forward five and a half years: I have moved from Thailand to France. I have been cutting on the handpiece for twice as many years as I had used the mast machine for. In the meantime, I have travelled around the world so many times that I can’t even count them. I have repeatedly gone back to the gemcutting hubs of the world to study the gemcutting history and traditions of Europe, North America, Thailand, and Sri Lanka. I opened two schools, wrote a book and countless articles, and have come into my own as a professional gemcutter.

Now, at my ten-year mark, it’s time to go back to school. My recent emigration to France has put me in the total mindset of all things French. I am learning the language and I’m also in the middle of a deep research project, documenting the history of the 600-year-old French gemstone cutting industry. A few years ago, I acquired a one-hundred-year-old hand cranked faceting bench from the rural mountains of France and it’s always been my dream to become an old man in a mountain cabin, spending my days hand cranking and faceting stones on it. The only problem is, I don’t know how to use it!

My hand cranked French faceting machine from around the 1910s. (Photo by Victoria Raynaud)

A few months ago, I decided it was time for something new and I bought a new faceting machine for myself. I have already spent years with both the mast-style and handpiece-style faceting machines and now there is only one major machine style left to learn; the jambpeg. I met both of the French manufacturers who make machines and picked out the one that I thought would work best for my needs (the FraLap). It arrived a month ago and ever since then, I’ve been obsessed with it. I’ve done as much research as I can in order to prepare myself for this new machine, however, as the jambpeg machine has always been the machine of professional cutters, there isn’t much information out there to learn from. There are no instructional books about jambpeg cutting and only a small handful of videos about it. It’s rare for a hobbyist cutter to use such a difficult machine and professional cutters don’t have much need to make instructional books and videos. Their training happens in the private world of apprenticeships.

At my age, it’s a bit late for an apprenticeship, but I have one secret weapon to help me; I know a lot of people in the cutting community of France, due to my past few years of research there. In the last month, I have sought out two professional cutters that I know to share a bit of what they’ve learned through their apprenticeships and professional experience. One of the teachers, Florian from Taillerie des Monts (one of the machine manufacturers) came to my house in Lyon and gave me a one-day lesson where I learned the basics.

My new faceting machine; the FraLap, a modern French jambpeg. (Photo by Justin K Prim)

Switching from mast machine to handpiece machine was pretty easy, as they’re not very different. Both use 96-index gears, both have protractors that go from 0 to 90 degrees, and both have a mechanical height adjustment, both use the exact same faceting diagrams. The jambpeg is a whole different beast and the transition is not easy. Not only is it physically different to use (and at first awkward), but your mind needs to approach the stone in a totally different way.

Imagine this; your dop stick is about the length of a pencil and only slightly thicker, but made of metal. The stone is attached with wax to the end of the dop. The dop slides into a metal hand-held case that has an 8-sided gear on it. You have an index gear on the case that lets you move 8 indices to the left and 8 indices to the right, so it has the equivalent of a 64-index gear, but it doesn’t work like an index gear as we know it. Everything has to work around the 8-sided symmetry of the case. Already your mind is melting. Mine has been melting for a month now, but as my mushy brain solidifies, it’s hardening into a new and better shape. And that’s just the index!

The mechanical stick in hand, with its 8 sides and the index gear inside. (Photo by Justin K Prim)

Now for the angles… there are no angles! Yes, it’s true. Instead of having a protractor to tell you exactly what angle you are cutting at, you have a metal box that sits next to the lap with a series of holes going from top to bottom (this is the jambpeg device itself, known in French as an évention, a two-hundred-year-old slang name that comes from the world invention) To cut the stone, you take your dop stick with its mechanical case and put the pointy tip of the dop into one of the holes. Now with the stone end of the dop, you lay down your dopped stone on the lap and whichever hole you’ve picked determines what angle the stick cuts at. You might be wondering why they don’t just label the angle on each hole. It’s a good question, but there is also a good answer. If you imagine that your mechanical dop stick is now resting on the lap and also stuck in a hole on the jambpeg, imagine what happens if the stone is bigger or smaller… the stick changes angles. The angles from the holes are relative to the stones size. I know, I know, your brain needs to reset now… don’t worry, the earliest American machines also worked like this and had no way to compensate for the angle change that a big stone versus a small stone would make.

The third control that any good faceting machine needs after angle and index is the height control, and luckily the jambpeg machine has this feature. There is a course height adjustment (similar to the height control on a Graves machine) as well as a little knob on top of the jambpeg that slowly makes the holes go up and down, allowing you a very precise and mechanically controlled fine angle adjustment knob. There is one more knob on the jambpeg, but to understand it we need to understand something that I haven’t mentioned yet. There is a flat metal plate sticking out of the side of the jambpeg. It’s this plate that gives the mechanical dop stick a resting place and which provides a reference for the 8-sided index gear. The final control knob on the jambpeg rotates the whole head slightly clockwise and counterclockwise which turns the metal plate and also turns the mechanical stick, so this final control is the cheater knob.

The hole you choose sets angle the relative to the stone size. In this 1912 photo, you can clearly see that the 8-sided mechanical stick also rests against the metal reference plate, giving it a rotational reference point for indexing and cheating. (Image from Gemstones And Their Distinctive Characters by G. F. Herbert Smith, 1912)

To sum it all up, the machine has an 8-sided mechanical stick with an index gear on it that can go +/-8. It has angle holes, but they are relative to the stone, not specific to a precise angle. It has a height control, a fine height control, and a cheater. The only other things to mention are a metal device on the left side of the lap that allows you to cut you table exactly at 90 degrees and a little dopping aligner that helps you get your wax dopping and wax transfers straight. This is everything that comprises the machine. Unlike American machines, you don’t need a collection of various shaped and sized dops. Since we are wax dopping and wax transferring, you really only need one dop, though I have three. There is no transfer block and no table adapter. Everything else happens by your hands, your eyes, and your skills.

The skill is the part that I’m working on now. It’s the hard part. From my two teachers, Florian and Liselotte, I learned how to properly hold the stick in my hand, how to do a full freehand wax transfer (which I’ve never done before), how to understand the jambpeg indexing system, how to translate some of my American-style faceting diagrams for use on this machine, and lots more. There are some things I really like and some things that I don’t.

This machine is built for speed and some of the benefits are really cool. For instance, imagine how long it takes to change from one angle to another. Add up all those seconds over the course of a whole stones and it becomes a lot of minutes, especially with a complicated design like a princess cut or an oval mixed cut. There is no need to change angles on this machine. When you pick up the stone to inspect it, it takes no extra time to put it back into a different hole, therefore changing angles. The same goes for rotational index. You can cut all 8 main facets on a round brilliant without changing any index settings at all. In the hands of an experienced cutter, you can cut all 8 facets in about 8 seconds (I’ve seen it done, but can’t yet do it myself)!

There are other things that I don’t like as much or are just frustrating because I’m new. Not having defined angles means my eye for proportion has to get A LOT better. The jambpeg cutters don’t window stones when they get used to understanding how the pavilion of the stone is supposed to be shaped. They also get to know their own machine and which holes will window the stone and which won’t. I’m doing all that, but it’s also not very hard to take a digital angle reader box and place it on my mechanical stick from time to time to check my actual angle, so that I can avoid windows.

I’m not sure if the jambpeg will replace my handpiece machine. I doubt it, as I’ve been cutting on that machine for too long and have become too fast in my work to slow down now for the sake of a new machine. Maybe after a few years of practice though, I would consider it. For now, it’s a fun experience that is teaching me to be a better cutter by improving my hand-eye coordination, my sense of proportion, my wax dopping and transfer skills, and more. It’s also teaching me a lot about the history of cutting and the history of French ingenuity.

As a final note about the importance and relevance of the jambpeg in the 21st century, consider this: When the first jambpeg was invented in 1821, it completely replaced the global cutting technology that was being used at the time (crude quadrant handpieces). When the French jambpeg was redesigned to incorporate the mechanical stick in 1888, it spread even farther around the world than its predecessors did. If we look at the cutting industry today, we can find jambpeg faceting machines (which all spawned from this original French design) in Thailand, India, Colombia, Israel, Brazil, France, Germany, England, Italy, and sprinkled through the cutting centers of North America. In essence, every major cutting hub in the world (except Sri Lanka and China) are using jambpeg machines to cut their stones. No faceting machine has ever been this popular on a global scale and it’s fair to say that almost all gemstones that have been cut on Earth for the last 200 years (including today) have been cut on jambpeg machines. That’s an impressive lineage that I would like to be a part of. So it’s time to go back to school…

About the Author

Justin K Prim is an American lapidary and gemologist living in Lyon, France. He has studied gemcutting traditions all over the world as well as attending gemology programs at GIA and AIGS. Justin has worked as a lapidary instructor for the Institute of Gem Trading and the Faceting Apprentice Institute and is the author of The Secret Teachings of Gemcutting. He writes articles, produces videos, and gives talks about gemcutting history.



Justin K Prim
Justin K Prim

Gentleman Lapidary | Author | Faceting Instructor | Chronicler of Gemcutting History