Cutting a True Blue Pebble into a Standard Round Brilliant with an Exceptional Eye.

A Tale of a Blue Tourmaline’s Missing Eye.

The day started slow like most days in the Borough of Mars, a small town about 25 miles north of Pittsburgh Pa, but the cutter’s heart was a bit a flutter because this could be the day for a new parcel of rough tourmaline to arrive from darkest Africa.  It had been a long time between parcels and it would be the second day in a row that the cutter would make the quarter mile trek to the post office on Grand Avenue.  The rough was here and an attempt to get a fast look at it while walking home was foiled by excessive tape on the final interior bag.

After finding a pair of scissors, the small bags holding the rough where laid out to examine.  It was a decent lot, but because of the great increase in the prices of tourmaline rough, it was not a very big one.  Most of the limited number of pieces of broken crystals and water worn pebbles would be straight forward to cut. The exception was a rather peculiar blue pebble that had been both ground by man and nature into a deep oval shape.  Looking threw the only reasonable side for a table I could see numerous inclusions.  They were both the reason why the beautiful true rough was not too expensive and be my major challenge in cutting a decent gemstone.  The rough had been sold as semi-facet, only small clean stones could be cut, but I soon felt that it was basically cabochon grade.  Now that I can not cut anything clean from this pebble, how can I minimize the impact of the inclusions I have to leave in.  Having the inclusions perpendicular to the table is the best solution to keeping them from flashing when the finished gemstones is viewed face up.  Fortunately the nascent table is generally positioned well and only needs to be ground flat.

The next challenge is to deal with the pebble’s dark ends.  The ideal way is correctly orient an emerald cut with the narrow end of the gemstone perpendicular to the c axis and with steep angled ends.  I have this thought in mind as I continued to look for a radial flaw (one parallel to the principle axis)  that just had to be in there.  There always seems to be at least one that can prove to be a threat to the integrity of the finished gemstones and requires removal.  While looking for the threat, I found at least one flaw that was parallel to the a/b axis/ nascent table.  This rough definitely was included with most of the numerous non threatening flaws at about 45 degrees to the principle axis.  All the flaws I could not get out, worked against making an emerald cut regardless of the dark ends.  Emerald cuts need a reasonably clean body to really shine because of the limited number of facets and lack of complexity needed to distract the eye from the inclusions.  Also Emerald cuts need a piece of rough that is not to darkly toned because a correctly cut emerald cut has to be deeper that most cuts.

Well I found my radial flaw and it did make marks on the surface of the pebble that indicate problems and I laid out my first saw cut.  Now I try not to use the faceting saw to remove flaws because it cuts way down on yield.  The rough was a good size at about 22 carats and with a rich enough tone level to make smaller stones, yet I still hate to waste material.  I really was not too careful with cutting the pebble because the small piece I would detach would have its table perpendicular to the closed c axis and be worthless.  But the cut would save grinding and I would get my first really good look at the pebbles c axis.

And what a c axis that preliminary cut revealed.  I had seen the pure rich sapphire like blue before in tourmaline.  It is very addictive, but generally needs a good light to truly appreciate it.  So, do I continue to make a significantly included emerald cut with steep ends or a round that will have basically the same blue color in both a moderate tone level (a/b axis) or a darker intense tone level, when viewed face up?   I defer that question while I grind out more flaws and thicken the edges of the pebble.  I am still searching for the cleanest areas of this rough and I finally it becomes clears that the thinnest part of the original pebble has the best clarity.  For once this does not make any real difference because the tone level of the c axis, while workable,  will need a relatively thin stone (small diameter) to be bright and beautiful under reasonable lights.  As the worst flaws are ground away it becomes obvious that a round is being born.  I let it happen because it is the best cut for both needing a thin stone and getting performance from included rough.

The next question is when do I stop grinding down the round preform and accept the flaws that have to remain in order for me to have any stone at all.  I can see that most of the bad flaws can be removed in the faceting process with most of the retained flaws being perpendicular to the table, so I stop.  I will probably only get about a ten percent yeild, but the war has been about getting a nice stone not a big one.  After doping, the reduction in diameter continues, but the really good news is that the 41 degree mains are eliminating flaws that endanger the culet.  Still I have to keep grinds and one of the flaws fails.  It is not a bad chip, but the girdle comes down again.  Finally the culet is solid and I have enough material for a normal crown and I stop.  I will have inclusions to remove when I facet the crown, but I think that the table and the immediate area under the table will be pretty clean.

After all this effort, the actual polishing of this magnificently colored indicolite (trade name for blue tourmaline) was a breeze.  None of the retained flaws cause significant marks on any of the facets with the mild exception of a couple of facets by the girdle.  Most important of all the table came out bright and flat, and without marks.  As I polish the gemstone, I am smiling because I know that I have done the best I could do.  The bright flat polish revels the heart of the round to be free of any major distracting flaws.  And the c axis color, the incredible sapphire like blue will probably not be too dense under most lighting conditions.  It is feeling good.  Still you never really know the final effect of a tourmaline until it is really done, cleaned and walked under a variety of conditions.  (I walk all my new gemstones to get them respond to different lighting.)

So what do I have?  The standard round brilliant had 41 degree angles on the pavilion and 40 degree angled mains on the crown. It is 8.6mm in diameter and weighs about 2 and half carats.  The play of the richly toned c axis and the moderately toned a/b axis make a distinct blue eye under day light.  It is a darker stone that likes the sun to make it really sparkle, but the eye is still distinct under shadier conditions.  There are no distracting flaws face up, but the stones flash is effected by the inclusions.  The difference is not a negative factor in my opinion.  Now with all that having been said about this beautiful gemstone, that is unique in the collection, I have save the best for last.  Under incandescent light, the gems a/b axis darkens to match the c axis brighter presence and the whole round becomes a vivid, uniform, true blue, flasher.  A color and display that any sapphire would be proud off.

It is late on the birthday of the storied stone and the passion of the day has slipped from my fingers.  Yet a smile lingers on my face as I think about another example of the incredibly variety and potential for beauty in tourmaline.

 

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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