In my last package of rough from Africa there was a very well worn, blocky piece of what appeared to be a medium light spice green tourmaline. Upon a closer look it turn out to be a bi color with about 1/3 green and 2/3 colorless. There are no indications of crystal structure and the material reminds me of some I got years ago from Del Gato which is the most northern of states in Mozambique. It is not the land of pegmatites that you think of when Mozambique comes up with tourmaline. The GIA tested some tourmaline from there and determined that some of it was Dravite the species. I have no way of testing the material to see if it is Dravite, but it would be neat.
Now the rough was well shaped for a pear and with plenty of depth. I don’t cut very many pear shaped gemstones so with the help of a friend, I decided to cut a deep pear shape. I did it in part to retain as much color in the culet of the stone as possible and have as much culet as possible in the gemstone. I think the strategy worked well and I have almost an 18mm by 10mm pear from the 20- plus piece of rough. Now I am on a roll, when I started to polish.
The polishing of this tourmaline has turned out to be very variable. A pattern of undercutting tells me that the c axis is nearly parallel to the table and not perpendicular as I would expect a bi-color’s table to be with this color distribution. (A layer of color in the culet and the crown a different color) Therefor I think I have a piece of tourmaline with a watermelon color distribution. When I am close to perpendicular to the c axis the facets tend to under cut badly and need special handling. I have used everything from a very light touch to heavy duty pressure with mixed results. The other key point to a nice finish is being absolutely in contact with the lap over the entire facet. Tables that have an undercutting problem tend not to have perfect finishes in my work. But I do make a concerted and time consuming effort to do the best I can on each individual case.
My alumina polish can quickly polish this tourmaline, but even away from the c axis, the facets are prone to undercut and even get significant scratches. Playing with the final polish to make it flat has taken a significant amount of time on some facets and leads to a bit of over cutting with my meets. Still I will take a flat polish facet over better meets, if I have to. And with this piece I have to. Still with this pear shape, I have both recut and repolished facets to get better meets.
I have about one more session with the polishing of this tourmaline and then I will transfer it. It will certainly be a significant/different addition to the collection and I will really try and get a picture posted. To be continued.
The pear shaped tourmaline is finished and it has been a trip. (There are a few battle scars) As with tourmaline’s that react strongly with my polish, you get a quick polish as long as you do not damage the surface. My technique of starting at one edge of the longest side of the gemstone in a plane slightly off the table and then lowering the facetor’s table as I try and keep the polished area, flat, worked like a charm. I finished the table without problems. With this sensitive tourmaline if it had marked it would have been a long trip to polish.
Now I like to think that I “own” the stone after the table is polish, but a slip on my part open up a girdle facet to cause problems. I had polished it earlier, but it would not cooperate again. Finally it cooperated, but it was so large that I had to adjust some facets. Any facet with a significant amount of the c axis continued to be very prone to problems and I was very glad to put down the hand piece with victory.
Now what do we have after removing it from the dop stick and cleaning it. In the first blush of bright sunlight I saw the yellow green I expected in a medium tone level. The color was pretty uniform, with only a slight indication of the colors 2/3s of the gemstone appearing in the point of the pear. I was a bit disappointed by not seeing more indications of it bi-color nature.
As the sun was setting over Mars, it was time for my daily walk and I always walk the new stones. In the setting sun light the stone still look rather “normal” and then I looked closer. I could see indications of a more forest green color at the point of the pear and the round end opposite to it. The effect was rather slight, but I knew where the c axis was for sure. After I stopped to talk with a neighbor, then I walked on and took the gem out of my pocket. The light was much bluer because the sun had set, and the gemstone was now completely divided into two parts. The pointed end of the pear that had a significant amount of the c axis had turned much darker green, while the rest of the stone changed very little. WOW. You would have not thought it was the same stone. I turned the stone 180 degrees and now both the pointed end and the opposite end were dark with only a wide band of a/b color separating them.
I have seen pastels pick up color after the sun goes down, but I have never seen such a strong change as this gemstone displays. Under indoor light the gemstone is back to looking normal (Basically just yellower) with very little indication of the c axis. But I know its secret and it is NOT normal and this is good for the collector in me that relishes different/strange tourmaline. It keeps me cutting because you really never know exactly what will come out from a piece of rough, from a different location/mine.
This one is going to be tough to photograph.