I could go into my history of obtaining rough that goes back over 60 years, but that would really only help an an old man recall memories. No, I want to address the effort to purchase tourmaline rough over the internet. My window on the process is narrow because I strongly believe in developing personal relationships with suppliers/dealers that last and my resources are too limited to investigate the trade in depth.
First thing I would like to press on you is that the purchase of all faceting rough is a gamble. In the case of tourmaline, that gamble can certainly be greater than many other types of gems. The increased risks are caused, in part, by the physical properties of tourmaline. I will focus on the following areas of problems with tourmaline rough, internal stress, color mixing, dichroism and the wide variety of dynamic colors, saturation and tone values. I will try and address each of these areas separately, but in the real world it is the sum of these properties, in perhaps a single piece of rough, that you will have to deal with.
Of course there are other factors besides the physical properties of tourmaline that can make the purchase of tourmaline rough interesting. Changes in consumer preferences, the feast or famine nature of the discovery and availability of tourmaline rough, all topped off with statements by “experts” that have spent years in the trade, but only have a passing interest in tourmaline. I will try not to fall into the trap of making statements or comparisons with other gem material that are too general when discussing tourmaline, the most complex gem of all colored gemstones.
There is little to be gained by looking at tourmaline rough when it comes to internal stress except for some guidelines. All bi-colors, tri-colors etc. and skins/coatings of significantly different. I have been told that a bell like sound when tourmaline rough is shaken against itself, rather than a duller sound, indicates stress. I have been told that grinding down the c axis first and then proceeding with cutting the tourmaline helps relieve stress. Now that I have told you what I have been told and not done, along with my observations, do I still buy beautiful rough with the observed faults? Yes, but with the realization that some of the rough will be more fragile and break. If I was unwilling to take significant risks with rough I would not buy tourmaline.
Now that you have taken the risk and the beautiful piece of tourmaline rough is yours, what can you expect? Some rough is definitely sensitive to any level of heating. I have been told that even observing a piece of tourmaline with a strong light can cause fracturing. And then there are the mysteries of cracking while grinding and even delayed cracking that only comes after you think everything has gone well. But the most diabolical cracks of all are the ones that run before the surface of the facet you’re grinding. It is maddening to keep loosing valuable material ant colors have areas of potential stress related problems. This is especially true when the color transition is well defined. I have found that if a crystal has been cobbled or clipped and the resulting surfaces are ragged or irregular there is or was a problem with the crystal. I have found that tourmaline rough that is heated will sometimes break immediately or may develop flaws during grinding. s the cracking continues a small distance below the surface. I have had limited success with speeding up the grinding process and clearing the flaw. That moment of joy is usually followed by the successful completing of the gemstone in the usual way.
With all the negativity in the last paragraphs, I need to affirm that most tourmaline I have cut is quite stable. A stability that can be marred by chipping on the culet or keel of your developing gemstone during both grinding and polishing. I have minimized this problem by not grinding too close to the finished location of vulnerable locatio ns with the coarser laps. My well worn 3000 lap has proven its value in the effort to polish out chips by limiting grinding damage to the gemstone.
The most important truth in the mixing of colors in tourmaline is that the c axis color can not be eliminated from any practical gemstone. I have seen large display gems that were tri-colors cut with square ends. Face up, which was the intended direct of viewing, they had a purity of colors even an emerald cut with steep ends can not match. There are assorted cuts for tourmaline and other dichroic gemstones that are designed to minimize the impact of the c axis color/dichroism on a finished gemstone. I have only tried steep ends of about 70 degrees on emerald cuts and did not like the lack of scintillation in the resulting gem. The flash in gems with dark, closed to semi closed, tone values of their c axis have stationary bands of flash, while emerald cuts with regular angles still have movement in their flash even when their c axis are completely closed.
I have cut some tourmaline with at least semi-closed end. The resulting gemstone lacks flash in the center even if it has some body color. And it can appear to have a less transparent then normal center. Still if the angles on the pavilion are correct, the edges of the gemstone can have vivid bright flash. The whole effect is rather like the windows you get in a gemstone with improper angles except you can not see threw the gemstone face up. I have cut gemstone with the at least sem-closed end so that the darkness is on the sides of the emerald cut. The best you can say about this is you get nice bright colorful ends that you wished filled the entire gemstone. Finally I have cut gemstone with their tables at 45 degrees to the dark/ C axis. If the rough has enough interest to cut and it came in stubby crystal, I would probably cut my emerald cut this way because I rather liked the way it looks. This does not change my opinion that stubby crystals with overly dark ends should be avoided. They do not produce high quality gemstones.
My solution to cutting tourmaline with any number of bands of color is buying rough with longer ratios between down the crystal and across the crystal. This solution also includes avoiding rough with a large ratio, but only a smidgen of color in one end. I search for color in tourmaline and if it is in multi colored rough that is great, but I will “waste” material to give the finished gem balance. Occasionally I have faced the challenge of a stubby crystal with an undesirable c axis. I proceeded to slit the rough parallel to the c axis and cut two small emerald cuts. If that is not reasonable, I again “waste” material by making “stubby” thinner and cutting an emerald cut. Being an undesirable c axis is not just a black white matter. I have come to prefer darkness, where I can see the desired a/b axis color without muddy ends. I adore bi colors that have great color in one end and are almost colorless in the other end. If the ratio is low enough you will have difficulty, face up, seeing which color actually has the color in an emerald cut. In longer ratio gems you will get a “pagoda” in the near colorless/pale end that can be very attractive and interesting. But if you find rough that is transparent and not attractive down the c axis, it is best not to buy the rough.