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Tourmaline Tribune

Dateline Saturday December 12, 2015

Problems with a significant (expensive) piece of rough minty tourmaline continues past the preform stage.  The piece of rough was rate AAA and had almost a preformed shape for a square gem.  It had a keel and a nascent table that had the only residual surface of the original crystal.  The original crystal must have been a good sized one because the rough was deep and the nascent table was parallel to the principle axis.  It weighed 22 carats.  The ground angles on the rough made it a pretty unusual shape for a piece of tourmaline rough.

After closely examining the rough the Iron Native (AKA the Cutter) decided to turn the piece on its head.  Even though this meant grinding away a significant amount of material in the old projected table area.  The angles just did not work for the most obvious way forward.  It soon became obvious that this was a good idea.  The rather shallow original keel turned out to have a running flaw.  I really don’t know if the weakness is generated by the grinding, but the flaw is not deep, but you just can not grind it out.  And so the thickness of the rough is decreased and the flaw has to be eliminated because it would be centered under the table.  Finally it curls up and is eliminated.

Now the Iron Native has to closely examine the corners of the preform.  It turns out that one of them has an open flaw that can be ground out, but reduces the preform to an oval.  The preform is ready to dop and he quickly checks its weight,  there has been a lost of about 40 percent of the original weight.  The minty tourmaline’s tone value is still high enough to make a pretty stone, but the yield has hit the wall.  As the Iron Native prepares to facet the preform he notices that the small amount of grinding that was done on the original crystal face has generated a tinny fracture.  The Iron Native knows that this trip to a finished gemstone could be a long one.

Earlier today this reporter observed the Native Cutter strike the top of his faceting machine’s table in disgust.  It was the culminating response to repeated failures of the minty rough and his continuing attempts to get something out of the mess.  The ultimate goal of the work had now been reduced from a thick oval to a thin round.  The flaws that had appeared were all parallel to each other, straight and not deep.  This is a parting problem rather than a cleavage problem, since tourmaline only has a weak indistinguishable cleavage.  Parting comes from the physical conditions that controlled the growth of the crystal and is rare in tourmaline.  It is probably the reason that the rough had been ground in an unusual way.  The change to the round held promise because the angles on the corners of the oval seemed to press right down on the weakness while angles that differed from the corners were grinding without problems.

In finally eliminating the breakage, before starting to make the bulky oval into a round, the preform was drastically unbalanced.  This combined with using a finer well worn lap to try and reduce the physical shock of the removal of material lead to an un-centered culet in a 10mm  round.  This is ridicules and the since all the breakage had been removed the Iron Native put on his regular rough grinding wheel (worn 360 grit) and took it down.  Now he did not abuse it , but there was some rather coarse mumbling.  Soon the pavilion was ready to be polish and it remains flawless.  The polishing process will begin in a couple of days, but since the girdle was able to be ground down without incident, the Iron Native is again optimistic.  He is going to get something pretty out of this tourmaline.  Hope does spring eternal in the heart of a facetor.

Dateline, Wednesday, December 16, 2015.

The standard round brilliant is finished and shinning with a natural zest, now that the sun has finally broken threw the clouds.  Its color is a medium pastel green with a side dressing of cool blue.  I would not call it a sea foam, because it is not dichroic and does not have the two colors to mix.  I would call it a complex color that is one of the infinite shades of green that tourmaline can produce beautifully.  I would not want to match it.

Will it break again during the setting process?  I don’t think so.  There are no signs of the parting problem in the stone.  It does have a tiny loop visible imperfect close to the girdle, but I doubt it will propagate.  Except for the tiny imperfection, the round has great crystal, a very clean look and comes in at 2.89 carats.  The Iron Native has succeeded in getting a 13 per cent yield in cutting a simple cut out of the triple A, 22 carat rough.  I am afraid that the Iron Native would be fired on this one, if he did not have a body camera on to show how close the owner (me) came to not getting anything from the rough at all, except brownish mud and fish gravel.

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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