Open C-axis?

[chrono]

Thank you for sharing what you can. It seems that there's both a positive and negative shift going on at the moment. Great for the locals to have more involvements and a share of the profits. Not so great that the bigger companies are playing in the same sandbox and potentially controlling more of the market. I see prices continuing to go up.

 

[Roger Dery]

Thank you for sharing what you can. It seems that there's both a positive and negative shift going on at the moment. Great for the locals to have more involvements and a share of the profits. Not so great that the bigger companies are playing in the same sandbox and potentially controlling more of the market. I see prices continuing to go up.

Chrono,
The issue of rising prices continues to hurt the custom faceters. Let's say they have rough purchased in 2006 and they paid $90 per gram for a particular type of item. They sell some goods from the parcel basing their selling price on what they paid. Then, they go back to Tucson a couple years later and the same dealer, carrying a nearly identical item, is now charging $120+ (or much more) per gram for the goods. If they are an aspiring hobbyist and have not been at the commercial end of things, they will be shocked!

It is possible, depending on their level of relationship with the dealer and whether they stay in touch during the year, they may hold them accountable - and move to someone else or another species. Then, come back a couple years later to Tucson and repeat the cycle.

For some time now we've been trying to ascertain the number of professionals working the cutting trade, and making a living from it. The number we've come up with is around a 150 or so. This does not include the hobbyist who has a day job, and facets a few stones a week in their off time. That 150 used to be over 400 in the 90's. So times are changing, and for those who desire well-cut stones your options seem to be reduced. Most unfortunate.

 

[Starzin]

This is a really informative thread - thanks to all for the Q+As. I wish there was a way Roger could post the resulting stone from that rough but it will probably contravene the rules. It would be lovely to see the stone that comes from the rough in this thread.

It also makes us realise just how tough the faceters have it to get some of the beauties we ogle. Much appreciated! The attrition in custom faceters is also disappointing though probably good for those who are left - not an easy business by any means.

 

[chrono]

Roger,
I appreciate your hanging around to continue to answer our questions. It's really a shame that the number of lapidaries have decreased. Although I may not necessarily seek out a precision cut stone, I do own a few and enjoy them very much. Not only that, I love seeing the various shapes, patterns and designs that are so unique and bespoke.

 

[gsellis]

Just to add...

With a closed C, cutting a tourmaline / emerald cut, the ends have to be very steep to minimize the opaque part showing in the stone. It will be there, but minimized. But the further negative is that 'flat' sides may eliminate the ability to use a tourmaline mount. No girdle to use.

With open C, there are two good reasons to cut on C. One is color. Sometimes, the color on C is better than on A/B. Watermelon tourmaline is a great example. A/B is green. C might be pink and careful use can get some of the green 'rind' in the edges. The other can be fractures. Tourmaline is one of those stones that likes to break by its own. If one end has multiple fractures, you may want to put that end (with obvious fractures removed) in the pavilion. There will be no mounting stress from prongs that might convince that end to go bang. But that has always been a gut feeling on my part and I have nothing yet to say that I am mistake. But then again, I have only cut 10-20 on C.

 

[chrono]

Glad to read more about faceting an open C axis tourmaline. This isn't the first time I'm reading about tourmalines wanting to break by itself shortly after being faceted. How common is this? Doesn't this make a lapidary hesitant to facet tourmalines?

 

[gsellis]

Glad to read more about faceting an open C axis tourmaline. This isn't the first time I'm reading about tourmalines wanting to break by itself shortly after being faceted. How common is this? Doesn't this make a lapidary hesitant to facet tourmalines?

I have not had one break on me, but I have had a crack keep going. I have a hint of pink tourmaline that I cut A/B that I chased the crack on the table almost to the girdle. It did not start out that far down.

 

[Roger Dery]

Hey George, thanks for chiming in - made some great points below.

With a closed C, cutting a tourmaline / emerald cut, the ends have to be very steep to minimize the opaque part showing in the stone. It will be there, but minimized.

This is true. And with a totally closed C axis, the angle on the end facets of a Tourmaline pavilion will need to be at 76* (or very close). C axis that are partially open, as in allowing a small percentage of light to pass, could be in the 72*, or even down to 68* depending on how open they are. Even at 68*, this is still complicated for goldsmiths to accommodate.

But the further negative is that 'flat' sides may eliminate the ability to use a tourmaline mount. No girdle to use.

And this is what the goldsmith will complain about - maybe not to the consumer, but definitely to the faceter who is responsible.

With open C, there are two good reasons to cut on C. One is color. Sometimes, the color on C is better than on A/B. Watermelon tourmaline is a great example. A/B is green. C might be pink and careful use can get some of the green 'rind' in the edges. The other can be fractures. Tourmaline is one of those stones that likes to break by its own. If one end has multiple fractures, you may want to put that end (with obvious fractures removed) in the pavilion. There will be no mounting stress from prongs that might convince that end to go bang. But that has always been a gut feeling on my part and I have nothing yet to say that I am mistake. But then again, I have only cut 10-20 on C.

I've had three Tourmalines come apart in recent years. One was being shipped back to me from a jeweler in California. Shipped by FedEx overnight - which is of course by air. We believe the loss of pressure, and possibly low temperatures experienced at 30,000+ feet may have relieved enough stress in the stone that it arrived in two pieces.

The other two were both Afghani pieces where it is reported they use heavy explosives to extricate the crystals from the hard rock. Both had lines visible in the rough when I started, but were gone after the pre-forming process - before I actually began faceting them. So I believed these to be solid pieces and continued cutting. One broke down when near finishing the pavilion, the other as I was near completing the design. Stuff happens and there isn't much we can do.

I should point out, that this is not the NORM. Tourmalines are faceted every day by many without any adverse effects.

 

[Roger Dery]

Glad to read more about faceting an open C axis tourmaline. This isn't the first time I'm reading about tourmalines wanting to break by itself shortly after being faceted. How common is this? Doesn't this make a lapidary hesitant to facet tourmalines?

Hi Chrono,
It is not common, and if the rough is reasonably clean, there should be no hesitation from the lapidarist. In fact, I find it to be one of the most enjoyable gem types to work with.

 

[gsellis]

Glad to read more about faceting an open C axis tourmaline. This isn't the first time I'm reading about tourmalines wanting to break by itself shortly after being faceted. How common is this? Doesn't this make a lapidary hesitant to facet tourmalines?

Hi Chrono,
It is not common, and if the rough is reasonably clean, there should be no hesitation from the lapidarist. In fact, I find it to be one of the most enjoyable gem types to work with.

I love the blues and blue greens. One of my favorite materials too.

 

[Roger Dery]

Sorry, as far as I know, no amount of cutting can do away with a closed C axis. The lapidary can, however, cut in such a way as to minimize its effect by choosing the right design.

Is true, no amount of cutting can avoid the Closed C axis effect. And yes, the lapidary CAN cut in such a way to minimize its effect.
Some examples:
samples of typical closed C axis Tourmalines


samples of typical open C axis Tourmalines


examples of C axis chosen poorly [this was handled by an apprentice about 5 years ago, working on their own material]
*and long since sold



Looking into the A/B axis of classic Tourmaline crystal

Looking into / through the C axis of same crystal

And if chosing well, here's two looking directly into a very open C axis on finished stones.
*photos of sold Tourmalines from 2009/2010



The Tourmaline discussion has been very interesting, and I thank you for the opportunity to share. Hopefully this will assist some of you as you make choices in the future.

 

[VapidLapid]

a colorless open C axis tourmaline






watch me break it!

http://www.youtube.com/watch?v=j8PpFdDyJ4I&feature=plcp

 

[minousbijoux]

But the further negative is that 'flat' sides may eliminate the ability to use a tourmaline mount. No girdle to use.

And this is what the goldsmith will complain about - maybe not to the consumer, but definitely to the faceter who is responsible.


I should point out, that this is not the NORM. Tourmalines are faceted every day by many without any adverse effects.

Sorry, but I don't think I'm following - what do you mean by "flat' sides and no girdle?

 

[VapidLapid]

Minous, the flat sides of the girdle, as opposed to trying to set a stone that hs no flat sided girdle which would be like a knife edge. Those hard to set and doomed to breakage.

 

[chrono]

Awesome eye candy examples as we learn more about faceting tourmalines.

 

[minousbijoux]

Minous, the flat sides of the girdle, as opposed to trying to set a stone that hs no flat sided girdle which would be like a knife edge. Those hard to set and doomed to breakage.

So are they saying that with steep pavilion angles, you don't have a flat girdle, but a knife edge? Why is this necessary? I'm still missing something here

 

[Roger Dery]

Minous, the flat sides of the girdle, as opposed to trying to set a stone that has no flat sided girdle which would be like a knife edge. Those hard to set and doomed to breakage.

So are they saying that with steep pavilion angles, you don't have a flat girdle, but a knife edge? Why is this necessary? I'm still missing something here

Don't despair, you haven't lost your mind yet. Two topics here:
1- The girdle line, as in found on the perimeter of an emerald cut, is at 90* to the table - with the table being at 0.00*. So, the girdle line is perpendicular to the plane of the table. Some cutting factories in developing countries will sometimes cut their girdles so thin that they appear 'knife-like'. This is dangerous for the stone setter as there little for them to work with.

2- with the girdle at 90*, and the first end pavilion facet at say.... 76*, there is only 14* bend to the angle adjacent - in the stone setter's way of thinking, this is hardly enough for them to work with. They [ideally] would like greater curvature between the two angles.

Hope you find this helpful.

 

[gsellis]

Minous, the flat sides of the girdle, as opposed to trying to set a stone that hs no flat sided girdle which would be like a knife edge. Those hard to set and doomed to breakage.

So are they saying that with steep pavilion angles, you don't have a flat girdle, but a knife edge? Why is this necessary? I'm still missing something here

I created an ugly example in GemCad. As you can see on the left and right, it is 'flat' up the sides on either side of the girdle. A prong cannot 'wrap' around it for a good hold.

 

[minousbijoux]

Perfect - I completely understand now! Thank you so much.