Closed "C" tourmaline tips

[hambiskit]

Looks like a good time to open this for discussion to me.
 Anyone have any tips on how to cut a closed C tourmaline they want to share with the new, or beginer's out there?

OK - basic's : Cut thru the A-B axis - increase the angles of your C axis facets to minimize darkening.
 Sounds easy doesn't it. LOL - well it isn't. Simple - but not easy. Keep in mind that when you move your angles - you are moving the critical angles that bend the light back toward the eye. So try cutting a piece after you "adjust" your angles to make sure that you get what you want from it.
 You can lower the crown , or raise the pavilion to shallow out the stone to help compensate for the saturation. Thin out the mix - if you will. Slight adjustments can have a drastic effect on the final appearence of your stone, so again - play with them to see what they do, and find that "perfect" one for you!

[mehoose]

Well, you know how a cut stone either has straight walls or bulges either straight or curved out to the side? What happens then if you went in from the sides? Wouldn't that make more dark areas in the AB cos you're shortening the 'c' in places? I'm following with the steep ends and if you thinned areas through the middle from either top or bottom of the AB.
Does this make sense? Tho technically would that not also make dark areas?
I'll be back when I get up, so thanks in advance and thanks for starting this thread Hamb.

[hambiskit]

Your right! That's why I said to shallow up your stone - keep in mind that the facet angles that parallel the C axis will be at least part closed, and darker.
 Now because every stone has a different amount of saturation - this will vary the amount of angle change you might want - too much and you will wash out your colors. I go 2* at a time until I get what I want. The more facets on the pavilion - the more the light will return not on the C.
 I use synthetics to experiment with because they are cheaper, and then a "practice" piece of real material to do a trial run.
 I cut a lot of Australian sapphires, good practice to learn how to cut dark materials, and learn saturation - not to mention a lot of re-cut practice.

But they aren't heat sensitive - and a fracture will kill your stone's dispersion. I don't mean to make it sound so technical...I just hate to be beat in the head by a rock - it's embarrassing.

[mehoose]

Ta Hambi.
 So the Tourm's are heat sensitive?

[hambiskit]

Very much so - even more so than opals. I only heat the dop to set my wax to cut the pavilion, and switch over to adhesive on the transfer. With high grade rough I only use adhesive mixed with baking soda.
 They will flash crackle on you faster than solder melt with silver - just takes a little flash of the torch & your done.
 I put the stone on the edge of the dop pot for a few seconds to warm it up a little (to avoid thermal shock), then schlack it before I try to set wax. I then drop wax onto the stone, and wax the dop separately. Let them cool, and then place the dop on top of the stone wax and heat the dop with the flame pointing AWAY from the stone until the wax melts like I want it as a hot joint, and then keep the dop upright, and the stone down until it cools. This keeps the heat from transferring to the stone.
 Use plenty of water while cutting, and a light touch on the quill.

[mehoose]

  Very interesting info.
Pulled out my tourms that just arrived from Beth for another peak.  My Rubel has formed anothery fracture in the cupboard! It did have a bit of an end but this is a newie. Does this happen often? Just with temp changes indoors? It's freezing so turn the gas heater on, it is in a shut cupboard tho so cooler than the room temp.
Which leads me to another question. If it does this in the cupboard, what happens after the stone has been cut? Can it still go 'ching' when worn in a ring going in and out of buildings or is it normally fine unless someone mashes their hand into something?
I've never set a Tourm yet in jewellery so wondering what info to give to customer when i do. I mean it's on the cards, the pinks and minty greens are yummo and looking to use them down the track.

[hambiskit]

They seem to hold-up better after they are cut. I haven't had any trouble with cracking, or chipping afterwards.

[mehoose]

Phew!
BUT...is that something that can happen, change of temp indoors during storage? Or is it just the quirk of some to let go anywho prior to cutting?
LOL, mebe it wasn't happy having it's jet setting life come to an end. 

[hambiskit]

Sometimes, and maybe it was the flight. Some tourmaline's are pyroelectric as well, so it may have created a internal charge enough to cause it to overstress the crystal from the flight variances in temperature. These are fairly rare to find - but if you do then they are really neat little buggers. Chances are 3-1 that you won't - but if you did you can rub it on your arm and drag it across (with rubber tipped tweezers) metal shavings and it will polarize like a magnet. Wearing it in a ring will create static charge...."and sparks fly from her finger tips".....sorry - mind flopper there...so you might get a little charge from it. Cutting it will take a little more time too. After cutting a little you may want to let it sit to "discharge" built up energy through leak down over night before continuing, how much it will build up I don't know - although it is a measurable amount. This will be created from the frictional heat created by the lap - so lots of water - room temperature - will be needed.

[mehoose]

oooooo..way cool  Hehe, can see a new film in the makin... the taming of the Tourm. 
Gosh, so many new things to try, tweezers and metal shavings.... oo and not to forget that cute SG kit from Beth needs to go for a whirl. It's all happenin Hambi 

[Beth]

There's a discussion about closed-c on gemologyonline:

http://www.gemologyonline.com/Forum/phpBB2/viewtopic.php?f=8&t=11832

Might be helpful

[hambiskit]

You want to move this topic to G.O.?

Think about this - how does Tourmaline grow? Where does the separation of open C axis, and closed C axis happen? I believe that the closed C material not only has a larger saturation of color - but sediment growth as well. Say if the crystal was a tree - the closed C would be the stump. This would make cutting it a lot easier - the open side of a 2x4 would be the long way the grain would run, and the closed the butt end. The growth "tubes" of the tourmaline on a closed C axis is quite a bit more course than the open C, this separation of the tubes causes the light dispersion not to return to the eye on the C until you polish the tubes enough to return the light to the eye. A blending of the tubes - if you will, or a polishing of the tubes until you actually polish the material in the sections between the growth tubes. Once you get this material to transmit light - the dispersion returns - opening the C axis. Because of the sediment growth on the C you will never get it to the same level as the A-B so proper orientation of this axis will be a deciding factor in the light return you get from your finished gem.
 Placing the C axis up to run with the table will give you a very dark stone, whereas cutting the A-B axis up will give you more light into the stone. Keep in mind that as we bend the light inside the stone that it slows down, along with this the saturation levels will slow it down, so the more we bounce that ray of light - the more of it will become extint. This is why higher levels of facets are predominantly used with lighter goods.

[hambiskit]

Here's a good reason I don't take pictures...this is a lot better in person, maybe Beth will take a better pic. of it.

[mehoose]

It's green 
Beth, you're services are required, LOL. 
Salright Hambi, my pics are about the same. Looks promising so far. 

[hambiskit]

  At least I got the color right!!