Cutting a stubby tourmaline with a closed c axis

As of August 2013 the supply of quality tourmaline available to the custom cutter  and coming out of Africa, has probably hit a new low.  I really don’t think much material is coming out of the rest of the world, but I don’t have good enough contacts to say.  What is available has become so expensive that I have to limit my quest for color.  In order to help me keep cutting a friend sent me some of his “spare” tourmaline rough.  One of pieces he sent and my wondering on the internet inspired this post.

Since I have my own site, I have been doing some more investigation of what the competition looks like out there.  The other day I ran into a site, that is bright, friendly and obviously both educational and set to sell.  I went to a rather long presentation about selecting rough and basically agreed with it all.  Still if I only purchased rough that meet all of his criteria, my collection would be less than it is.

The tourmaline crystal my friend sent has completely dark ends, (optically dense looking down the c axis) and fails the reading newsprint threw the lighter a/b axis . (A common way to test tone level.  You need a decent light and I move the rough to try and see the print more clearly)   Looking threw the crystals you can see a nice blue-green color, but looking threw a crystal is not the recommended way to judge tone level.  But it is excellent for picking up flaws, if you rotate the rough around.  The rough, which has bright crystal sides, did have some “clipping” damage (Rough dealers break out sections of crystal between flaws rather than sawing them.  It is quick and can be clean, but at other times it can produce damage.)

That said, what does this piece of tourmaline rough have going for it and why would I bother cutting it.  It has its size, a nice a/b color and cleanliness going for it.  (probably at least 15 carats in size) In order to cut a practical gem from a closed ended piece of rough, I have to place the darkness in the end of an emerald cut with steep angles on the ends.  The emerald cut’s ratio should be made so that the gemstone is relatively narrow.  Making a narrow long gemstone will also reduce the thickness of the finished gemstone, even with the proper pavilion angles, and help permit the a/c color to be light enough to produce a fine gem.  ( if it start out with a fine color)

So lets begin the preforming process.  It really did not take more than a quick glance to see that the rough had good color, had a clean center, completely dark ends and a level of tone that would be good in a much narrower gemstone than the rough’s present thickness.   Finding flaws and working with them and the color distribution in the rough, while still attempting to get a decent yield,  is absolutely critical to success, so take your time if you need it.

I got out my dusty diamond saw that is specifically designed to minimize the thickness of the blade, to conserve material.  It is dusty because I really try hard not to use it very little.  Whenever I use it, I know that I will not be getting a very good yield form that piece of rough.  I cut the rough down its middle parallel to the shiny sides of the crystal. (down the closed c axis).   The flat surfaces produced by the saw are the nascent tables of the two emerald cuts I will make.   I put on my old trusty 360 mesh standard lap and start limiting the amount of darkness in the final stone by grinding off the shiny sides of the crystal perpendicular to the nascent table.  Since you are working for a long  relatively thin gemstone,  I work toward that rather than worrying about yield.  It is a shame to grind tourmaline into brownish paste, when I have the thickness to cut a wider stone,  but the widest stone I could cut in this case would be too dark in every dimension.  I am careful to remove only enough material from where the crystal was clipped to clean up the damage and square the ends.  The more length I can retain from this dumpy piece of rough, the wider I can make the gemstone and still have a good ratio.  With this rough, its tone level  has gotten good enough to support this kind of conservation of weight.  I am careful not to remove too much depth (especially from the steep ends) as the preform is getting considerably smaller and it is grinding quickly.  The safest way is to just dop the preform, with very little reduction in preform depth and grind the material away while faceting.  Still if you have doubts about the rough’s tone level, the careful removal of excess thickness should help you determine the final dimensions of your emerald cut.

So now the preform is completed.  Its ratio of length to width has been modified drastically from the dumpy piece of rough you started out with.  Your yield has been terrible, but that is to be expected in the world of dumpy closed ended tourmaline.  In fact, with this piece of rough, its size was the critical factor in saving it from being junk in my world.  That it had good color and purity helped, but would have not save a small dumpy closed ended tourmaline from the land of the lost on my kitchen window sill.   The cutting of the preform into a nice gemstone should be routine.

Good luck with your tourmaline projects, but please do not spend very much money on dumpy closed ended tourmaline without being very critical of their value.  I very seldom buy rough like I have discussed in this post, but times are hard and if the color is good….  COLOR IS KING.

Bruce

About Bruce Fry

I was born in Summit, NJ in 1947 and graduated from Summit High School in 1966. I graduated from the Colorado School of Mines in 1970 and after spending another year in graduate school, I left to see the world of Brazil. After spending some more time discovering myself, I ended up working for the Commonwealth of Pennsylvania for 32 years as an Air Quality Engineer in the Department of Environmental Protection. I retired in 2007 and took up faceting gemstones again after a long hiatus that reached back to my twenties. I had started cutting cabochons when I was 13 and bought my first faceting machine when I was 15, but ran out of money and time until I retired.
My great love in gemology is tourmaline and the collection presented here represents my effort to get as much beauty and variety in the colors of tourmaline as I can. I was particularly lucky in being able to get unheated cuprian tourmaline before copper was discovered in gem grade tourmaline from Mozambique.

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One Response to Cutting a stubby tourmaline with a closed c axis

  1. Allan says:

    Hey Bruce – glad you’re getting to cut something! Love to see some photos of the process and of the stone during/after…

    Keep up the good work!

    -Allan

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