Published: 13 January 2020

Years ago, when I wasn't into gemstones at all, I thought the most important part of gemmology was the art and knowledge of cutting (especially faceting). I thought it would be an incredible amount of work and difficult to get it done right. The origin of, and differences between, the different kind of gemstones seemed less complicated to me. They just came from a few mines somewhere far away in a tropical jungle (watched too much Indiana Jones).

There are many different cuts, but that is the subject of a later post on this site. Wisdom comes with age, and now I know better. In gemmology it is precisely about the origin, identification and properties of the various noble materials. Faceting is the use of this material, and is therefore something different, more of a craft. I find this odd in a way. Grinding, processing, faceting should be the core of gemmology. After all, it is the process by which raw material is transformed into a gemstone, a kind of transubstantiation so to speak. But I digress.



Faceting is done on a faceting machine, which consists of a rotating grinding wheel, cooled by water. The material to be cut is attached to a stick (“dopstick”). This dopstick is then attached to a mast assembly with which the angle of the material relative to the disc can be adjusted, and an axis around which the material can rotate. This allows cutting facet by facet. Since a "simple" brilliant already has 57 facets, it is immediately clear that it is rather complicated.

Don't you also find this not so clear at once? Me neither. These kinds of techniques can only be understood (by me) through “learning by doing”.

Now it is a bit difficult to just get started with such a device. As a real IT person, I therefore looked to see if there was any software for it. Well, there it is. I downloaded gemcutstudio and after a few hours and a tutorial I even understood how to cut a brilliant. I then set out to reverse engineer a cushion-cut yellow Cubic Zirconia, and see if I could get the cutting instructions for this physical stone into gemcutstudio. And of course I wanted to see if the end result was a bit right.


After measuring the stone and determining the layout of all facets, I entered everything into the software. After (a lot of) fitting and measuring, the result seemed to look quite professional. Slowly but surely I also understood how faceting works. With software you can make mistakes, without forced to start again with a new stone.

The most important insight was that faceting in this way resembles working with a lathe, and that the symmetry of the cut will feel natural.



Another advantage was that I am now able to read the "recipe” of a design.

After the design is ready, you can start simulating the appearance (via ray-tracing). At first, the calculated picture didn't look much like it. It took quite some effort to get a somewhat similar image with small changes of angles and symmetries. Especially the characteristics of the pavilion surfaces listened very closely. The end result still differs a lot from the original, but there are also great similarities.

 cushion cz

These deviations can have various causes. The lighting of the simulation is different, the girdle has been ground round in the original CZ (this is not possible in gemcutstudio), the angles have not yet been chosen correctly by me, or the rotational symmetry is different. The latter is a bit technical, but the dopstick is attached to an index wheel, and it has 96 positions in my design. If there are more or less, the angles between the facets get different values, which leads to a different result.

Still, I'm not dissatisfied, and you can even make a moving simulation.


Conclusion: it's actually all pretty nice. In the near future I will visit a real human cutter to see what this looks like in "real life". A course to make cabochons is scheduled to do in the autumn.

UPDATE 2021: Both goals were reached in 2020. Due to Corona there were of course some hurdles to get it completed.