They say that the third try is a charm and so I am ready to tell a charming story. It is about a most peculiar type of tourmaline that has a watermelon distribution of color. It has a central core of a fine pastel orange and a clear skin of tourmaline that looks like melted uncolored wax. Now I have been drawn to this material a total of three times in the last three to four years and each time I have had catastrophic failure, until last night.
Last night I finally finished a 5 millimeter round and gained greater insight into polishing “difficult” tourmaline. Now this material is fragile and you have to be careful with grinding it. My early failures were in the grinding phase. And when this material fails it is not just a feather that perhaps could be lived with, it is a complete separation of the crystal in a plane perpendicular to the c axis. But this last round, of the battle with cutting a longer ratio emerald cut, went well into the final rounds of polishing the ends on the pavilion.
The long thin facets on the side of the emerald cut had gone very well and I thought that the this was because they were in the clear skin of the watermelon style crystal. How would the peach core react? Well it did not go well. If I did not keep my pressure light, I could easily rip the surface off the gemstone. This damage was so difficult to remove that I ended up recutting the first end I worked on. Now that I know of the pitfalls, I carefully finished both ends and went to polish the small corner facets that are usually rather trivial. (The gemstone would only have been a couple of carats at the most) Well I needed to move the corners a bit because of recutting and I arranged to come in at a bit of an angle to the cut facet. When I started polishing I could sense the stone vibrate and that was all it took. It instantly broke. I popped it off the dop and it fell into two pieces. With disgust I put them on the kitchen windowsill, which is the land of lost stones in my world.
Rejection is hard to face, but I still have another piece to facet, since I split the long thin crystal of water worn rough in two, to make practical gems. I had never focused on vibration caused by polishing before and I wonder if the difficulty in polishing the ends was tied to the vibration of the stone. If it was, the effect must be subtle, since I did not cause the gemstone to squeal or anything like that during my problems. I was being nice.
Well there was only one way I was ready to move forward and that was to regrind the end of the bigger fragment of the emerald cut into a shorter emerald cut. The break was clean, but after playing with orienting the partial gemstone without recutting it all, I got fed up and made a round out of it. I could answer my polishing question and maybe get a gemstone out of the rough at last with a simple round. My dop sticks certainly support a round much better than an emerald cut.
I quickly ground the piece round, almost daring it to break and end my misery. It took it all like a champ. In fact everything worked great. It took a beautiful polish that accentuates it great crystal qualities and pastel peach color. I did not notice any difference between the core and skin of the tourmaline.
So what have I learned or relearned on my quest for beauty in tourmaline? Tourmaline has a reputation of being a very easy material to polish. And in many cases that is true, but tourmaline’s complex nature can conceal stress and present inclusions that can make finishing a gemstone difficult. The tourmaline I worked on here is a pretty extreme example of a gemstone accepting compressive force while being extremely weak under tensile force. The difficulty in polishing the ends, which I ascribed to the properties of the core, really centers on support from the dop stick. This stone is weak while being ground and a delicate polisher, but good support should make it possible to finish a reasonably sized emerald cut.
Now, I must try out my speculation. But first I have to get my goldsmith friend to grind down one of my larger flat dops to the right size for my last piece of this variety to tourmaline that I will ever get, regardless of success or failure. A success after most of three failures is enough for me and a forth failure, impossible! Still there is more rough out there, that has the same trap for me and now I will be better prepared for it. At least I think/hope so.
I will confess my success or failure to you when it happens. (12/2013)