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 Post subject: Orienting tourmaline rough for beauty.
PostPosted: Sat Mar 09, 2019 1:19 am 
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In my effort to know what is out there on the web about tourmaline I have read a lot of mistakes. One item that keeps popping up is that tourmaline is difficult to cut properly. The difficulty with tourmaline seems to come from its crystal shape and dichroic nature. In this post I will try to get under the covers of this general statement about tourmaline, based on my experience with cutting tourmaline for beauty. I am not going into the many ways that tourmaline can terminate its self and break my heart.

If you're willing to not buy any tourmaline rough that is not ideally suited for cutting, this post has nothing for you. My dream rough basically comes in two varieties, One of the glories is a pencil with beautiful color and good tone values down the principle axis and perpendicular to it. The second type of ideal rough is a nodule with beautiful color shining up from its pure heart. If I had waited for only this kind of rough my collection of tourmaline would be much more limited and less interesting. Great colors seldom come in perfect pieces and if such pieces happen to be found, you will probably never get a chance to buy it.

The next classic style of tourmaline rough that i would like to discuss is a long/short rather narrow crystal shaped like a section of a pencil. Its principle axis, which is down the length of the crystal, appears to be darkly toned or completely dark/closed. I say appears to be darkly toned because it can be difficult to judge long crystal sections. I don't use powerful light to evaluate rough and bright transmitted light can be deceptive in evaluating tone values.

In the past I used to cut the ends of semi to completely closed tourmalines with steep ends. I really did not like the play of light in the finished gem or cutting down the corners of the emerald cuts so much. I therefor, cut all my tourmalines with tone problems with normal angles. (They are also easier to set.) I should talk a bit abut tricolors/tri colors. The angles at the end of their emerald cuts do effect the amount of blending of the colors in the ends of the gems. I accept the "pagodas" of blended color and try and cut emerald cuts with significantly high ratios to minimize the blending's effect on the overall color balance of the gems. I can't say that I have had a really bad blend, but then I don't cut a lot of bi/tri stones.

To be continued in another post.

Bruce


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 Post subject: Re: Orienting tourmaline rough for beauty.
PostPosted: Sat Mar 09, 2019 7:48 pm 
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Bruce,

Great write-up and I learned a lot. Here's a question that may have a "it's personal choice" answer. As an example, I have some light grass green color tourmaline in decent lengths and widths that when viewed down the C axis have a beautiful yellow color.

If I sawed the pieces into shorter lengths and cut rounds, squares, trillions, Etc with the table on the C axis. Do you think the yellow would still be there, or is it a function of the length of the original crystal (say 2.5CM long), that's giving off the color?

My thanks,

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Bob Hodges

Faceter: When turned into a zombie, they stumble around crying "roooouuuuggghhhh"


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 Post subject: Re: Orienting tourmaline rough for beauty.
PostPosted: Mon Mar 11, 2019 11:14 pm 
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I recently cut a tourmaline crystal that I think was similar to your material with a good strong yellow down the principle axis and a rather pale greenish a/b axis. I lost a lot of weight, but I was determined to get the purest yellow I could, by placing the table of the gemstone perpendicular to the principle axis. The yellow certainly dominates the small shield cut, but the eye is very sensitive to green and there is a touch of green in the stone. I could have cut a larger emerald cut with the principle axis (yellow) out the ends of it and be more commercial, but the rarer yellow was my
interest.

I have a few rarer occasions when more difficult rough presses me to produce a nice gem and retain at lease a decent amount of the rough's original weight. If the nodule is on the flat side and you really don't have enough material for good angles on the crown and pavilion for it's round diameter, I have found an oval might be a better way to go. I have experiment with flatter crowns down to ones with 25 degree mains, but I don't like to go below 35 degrees now I have to confess that I have not been privileged to cut many nodules fresh from the cobbler. Most of the rough that I have been able to obtain, that I think were nodules were completely water worn. I might add that when a stone is clipped, (like cutting you nails)a form of cobbling or breaking the crystal, if the end that is produced looks splintered, the rough has problems.

I should add the story of a stone that still sits with a glow in my memory. It was a thinner section of crystal with both a dark principle axis, but not closed and a nicely colored a/b axis. Cutting a round etc with its table perpendicular to the principle axis would produce both a pretty small stone and one that would be dark. I decided to place the table at forty five degrees from the principle axis. The enabled me to cut a wider emerald cut/oval etc. and have a gemstone with flashes of lighter color a/b mixed in with the dark c axis color. The mixing of the different flashes of color did not cause any problems and I liked the gem. I have use cutting the table in at 45 degrees to the c axis many times, just to get a better yield and it has not failed me color wise.

The orienting of rough tourmaline to minimize the distraction from flaws that can not be reasonably removed from the finished gems can be fun.. ( the removal of radial flaws and skin does not really effect the orientation of the tourmaline for color, but it is usually needed to protect the integrity of the gem, limit the chipping of the keels and make a pretty gem.) I have purchased a number of hunks that were sold as "cab grade or semi facet grade" with a nice color. I like good crystal between the flaws. The flaws in these pieces are generally randomly oriented. I try to do two things with the flaw that will remain in the gemstone. Keep the area under the table a clean as possible and have any residual flaw as close to perpendicular to the table as possible. Flaws toward the girdle should be kept kept deep enough in the gemstone as to not endanger the integrity of the girdle.

A couple of recent examples are in order. The most of fifty carat piece of of bright pastel blue green was only faintly dichroic. It had some major flaws that would have to be sawed (never a need that produces good yields.) along with feathers that could be left in without endangering the strength of the gem. It took me hours of focus on the rough to produce four preforms. They would never be clean, but their hearts were decently pure and the color was still there (not too pale). The piece of rough had been completely cobble before I received it and no one will ever know how flawed it was or the time it took me to cut them, but I find great satisfaction in their beauty. Something of beauty from very little is very satisfying to me. It is a bit sad that I only got a 15 percent yield.

The dark blue piece of rough looked more like a thick elongated pill that is easier to swallow than a round one, rather than a tourmaline crystal. Its shapelessness had come from millions of a years in some African stream. The blue was very dichroic with a semi closed c axis. The a/b color was a good blue color. The rough was not fractured, but contained long rather thick white billowing clouds parallel to the c axis. A rather unusual inclusion. My aim with this piece was to get the clouds as close to the girdle without destroying it and making as thin a gemstones (with the right angles) as I could. The rich c axis had a great saturation and really was beautiful in enough light while the a/b axis had a good tone level. They mixed beautifully and the need to get as light and flashy a gemstone as possible drove me to a round. In the end I got a gem with flash in normal light from the a/b and plenty of blue oomph from the great blue c axis. The clouds can still be seen on the sides but they are mostly hidden by the stones rich tone level.

I have only cut one "watermelon" style tourmaline into an emerald cut. Most of the the rind is either too narrow, included or irregular to be retained in the gemstone. There certainly aren't any problems picking the cut or orientation if you can get the right piece. The bands of color that is produced and richer tone at the ends of the emerald cut are exceptional.

Oh and I almost forgot growth tubes. I have not cut many tourmaline with a real problem with them recently. I try very hard to remove them from under the tables of my emerald cuts and position them perpendicular to the tables of the stones displaying the c axis color. Growth tubes are always parallel to the c axis. I once had a really great spicy green color that had such thick growth tubes that I could see where they penetrated the table with my eyes. They did not effect the beauty of the stone much and color sold it.

With tourmaline there is always more, but I think I have covered most of the fun you can have with cutting tourmaline for beauty. The hardest part of doing it is all the waste that can happen doing the job right.

Bruce


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 Post subject: Re: Orienting tourmaline rough for beauty.
PostPosted: Tue Mar 12, 2019 9:08 am 
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Bruce,

One heck of a piece of writing there. I had to read it twice to catch most of it (and probably more to fully digest it). However, I love the idea of the 45 degree slice. I have two of the grass green with yellow C axis and I may just try that.

Take one, slice a section and cut a round brilliant and see how much yellow I obtain, and then take the remains of that section and cut it 45 degrees and then I'd have half a preform for another round. Should be great fun and an interesting look into the orientation and results of tourmaline.

You're truly a wizard with your collection and thank you so much for sharing.

My thanks,

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Bob Hodges

Faceter: When turned into a zombie, they stumble around crying "roooouuuuggghhhh"


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 Post subject: Re: Orienting tourmaline rough for beauty.
PostPosted: Tue Mar 12, 2019 11:55 pm 
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Thanks Bob for your kind words. One of the joys that I find in cutting tourmaline is never knowing in many cases exactly what color will be in the finished gemstone. The dynamic inter action between the c axis color and the a/b axis can also be fascinating.

I took the blue round for a walk after digging it out of the collection. We had a rare day with bright sunshine and the stone loved it. I also took along an emerald cut that I cut, from Namibia.

its colors are almost identical to the round, but the round picked up more of the rich blue c axis color. There were still wedges of lighter blue a/b color in the round, but they were not as noticeable as the same blue in the ends of the emerald cut. This help make the round look a more vivid blue in direct sunlight. But when i walked into the shade the c axis in the blue round shut down and the stone only had the a/b area to keep it flashing. This gave the emerald cut the edge in beauty in the shade. Oh its c axis color also went dark, but that impacted on the gem was less because of its cut.

Have fun with your stone

Bruce


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 Post subject: Re: Orienting tourmaline rough for beauty.
PostPosted: Wed Mar 13, 2019 9:53 am 
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Bruce,

I can only hope for the day when I can cut something I'm as proud of that I want to take it for a walk in the sunlight. I continue to look through your collection here and it's truly awe inspiring (especially some of the pinks and reds).

Thanks for sharing your work and knowledge

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Bob Hodges

Faceter: When turned into a zombie, they stumble around crying "roooouuuuggghhhh"


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 Post subject: Re: Orienting tourmaline rough for beauty.
PostPosted: Wed Mar 13, 2019 3:31 pm 
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Pride in the joy of creation is one thing, but more important to me is appreciating how the gem responds to the many faces of natural light. I continue to be awed by the range of color and its presentation in tourmaline. And it makes me smile.

Bruce


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