A couple months back, I bought a huge 82ct premium color tanzanite that had been badly heat damaged, likely from a (very inadvisable) steam-bath. Given the quality of color & size of the stone, whoever broke it took a big financial hit.
The image above suggests it would be best to just divide the stone and make a matched pair of rectangles. But, unfortunately, that obvious fracture curves and twists inside of the stone. And it brought some friends along.
The side view isn’t much better:
So, the stone needed to be divided along those fractures lines and any unstable areas ground away. Here’s what I ended up with after spending some careful time with the trim saw:
All together, these fragments weigh about 72.25ct. Really that’s not too bad given the amount of damage that had to be cut away to make useable rough pieces. Those two fragments in the center are wastage; they’re too thin/fractured to be useful.
But making random shaped tanzanite roughs adds level of challenge: the final color of a tanzanite gemstone is dependent on its orientation. There is only one axis in tanzanite that gives the rich, purplish blue top-end color. So I had a choice — maximum weight yield or better color using more interesting shapes & designs.
Maximum weight yield would have given me mostly step-cut rectangles (tourmaline and emerald cuts) of various proportions; the kind of stones that are standard everywhere in the gem market. But accepting a little more weight loss provides the opportunity of being more creative with designs — and better color is always better. Giving my custom jeweler friends something much more interesting to work with. Why cut generic anyway?
4.18ct Diamond Cushion Brilliant
3.48ct Shield Brilliant
5.36ct Re-Echo Cushion Bottom
4.40ct The Long Hex Step
1.28ct French Cut Rectangular Cushion
3.55ct Custom Oval
In the end, I was able to recover 6 stones with for a total of 22.25ct from the original 82ct tanzanite, about a 27% yield. That yield looks small, but it’s comparable to cutting these same stones from rough, so well within expectations for custom cutting.
And the best part is that a damaged & essentially useless large tanzanite has been transformed into high quality gems ready for mounting. I can’t wait to see what you do with them!
Curious about how the giant tanzanite was damaged in the first place? Check out: Heat Shock in Tanzanite