Art #13

The cutting edges (3D)

We now know a little more about the history of one of the emeralds of Catherine the Great of Russia. Just for sport, how about trying to 3D model it in both of its known historical states ? As this is merely a beginner’s exercise, and the web is stock-full of information from more competent persons, hereafter are the few things I tried to do, as ill-advised as they were !

The table, the crown and the pavilion: it’s all about edges

Let’s start with a little observation and a dash of vocabulary.

Precious and semi-precious cut stones are described using a very precise topography related lexicon. Simple, easy and efficient.

Quick and dirty anatomy of a cut stone

The optimal angles of all the facets in relation to the stone’s size are a constant research, and it is now also a subject for artificial intelligence neural networks to deal with. All these maths make my brain hurt.

In 1874, we know the stone had a rectangular looking cut. If we refer to “canon” cuts, it can either be “rectangular” or “emerald”. Or, and alas more likely, a variation using a little bit of both…

Remember, the brooch was looking like this:

The corners of the stone do not look cut at 90°, one of the characteristics of the emerald cut. So, it seems the stone might have a classic rectangular cut. However, the table size seems larger than on the models I could look at.

The emerald is now pear shaped. Here are two hypotheses as to the stone’s two historical shapes, side by side.

Note the topography of the backside relief of the rectangular cut is showing baguette shaped facets and the pear cut has a star shaped effect down to the culet.

Here’s what the stone looks like now.

Extract from https://www.christies.com/lot/lot-the-imperial-emerald-of-grand-duchess-vladimir-6199493

The crown seems almost regular for a pear cut. The transparency of the stone lets no doubt as to the verso: there’s nothing standard here !

One might think the lapidary reused part of the initial rectangular pavilion ? That is almost surely the case. Having to recut such an important stone, one will try to keep as much matter as possible.

While we’re at it, let’s take a brief moment to appreciate the jardin of the stone (inclusions and cracks, in case you forgot our first foray into that area) and its slightly yellow hue.
A russian emerald from a columbian mine ?

The pavilion seems entirely modified from the standards. The culet isn’t peaked, but rather rectangular as far as we can extrapolate from the picture.

What about modeling then ?

This emerald is interesting in two respects for a rookie modeler. It emphasizes two essential things in the 3d modeling process: shape and lighting.

I know, you cunning reader ! You’ve already noticed that gemstones are transparent. They let the light in and refract some of it. This is where the lapidary art lies: knowing how to use the rays entering the stone by the table and reflecting them among the facets. A fire from the inside !

Progress of digital render engines makes that digital rays of light on a scene behave more or less like the real thing. In order for our 3d model to work as a historically accurate element, it needs to imitate the shape of the original as closely as it can. Otherwise, the effect won’t work: the stone won’t look like it does on the archives we found.

This is where I started to have second thoughts about choosing that very model for an exercise. But it was too late, I was already in.

Let’s start with the 1874 version of the emerald: a simple (-ish) rectangular cut. According to the documents, the table looks large and there are two rows of baguettes around the crown. I was not able to find profile views, so the dimensions of the girdle are conjectures based on reference models.

The pear cut version of the stone is harder to create. We only have one good view, front facing. All other views I found were of the stone inside the necklace it now lives in. So, we’ll have to be creative and make educated guesses.

The overall aspect of the stone is both related to the pear and the rectangular shape. We have to create a chimera that links the two shapes as harmoniously as possible. We know the emerald lost weight when it was recut, more or less 31 carats. What we do not know is where those carats were on the original shape. Because one has to start somewhere, I chose the version where the pear fits inside the rectangle, perfectly centered.

Something along those lines:

Because the idea behind recutting the stone was to get rid of too prominent inclusions, it may have been a completely different approach. I couldn’t make out exactly where and how the inclusions were using the documents I found.

You’re still there ?
How brave of you.
Moving on !

After what one would call a concerning amount of trials and errors, here is the chimera that seems to tick all the boxes:

Colour, reflection and et refraction

We now have to tackle the texturing of the stone, mimicking the emerald, from its hue to its jardin and its transparency.

A web search offers numerous examples to follow to create an emerald like “shader”. As this is an exercise, I first decided to go rogue and start one from scratch in order to learn the most things possible. And learned a lot, I did.
But as far as creating a decent emerald material, not so much.
My results were lacking depths or fraction, had sometimes poor transparency and the jardin was missing or overly present. I went back, ego slightly bruised, to the net’s advice.

The best shader I could find was, for me, M.Pilon’s one. I tried to adapt it clumsily to our emerald’s case. My results are not really good yet, I’m afraid. I also learned a lot from this, including proprieties I never knew existed (and that I will need time to understand!). I also learned that too many scintillations on a screen gives me a headache.

Here are a few results of my tribulations:

I chose the “C” version and tried to rework it to try and grasp the hue nuances and the jardin of the emerald.

Texturing path and very, very messy PBR shader !

One has to keep in mind that the lighting used when shooting the reference picture of the stone is tremendously important for its final aspect. Once again, on that matter, we can but only have educated guesses. Moreover, the reference image probably underwent post production retouching.

So far, here are the two 3d stones we got:

Shake it up !

Now we can finally show one becoming the other (because that’s what we were aiming for long long time ago, remember ?).


After all these adventures, you have earned the right to go and rest a little !
Maybe go watch paint dries on a grey wall ? I don’t know about you but for me, that seems like a very tempting idea right now…