Citrine: Where to find a nicely cut stone

[Richard M.]

Tony,

Yes, I had noticed that but thought it might be a computer artifact. I haven''t had time lately to pursue cutting the design which is for beryl, not quartz as I originally said.

I''d very much like to see your "tweaked" version.

Richard M.

 

[Proteus]

Richard,
Here's the modified version. I had noticed the original was for beryl, but I figured I might as well modify it to work for quartz as well. I tested rendering the original with beryl's RI, the window was quite huge. One issue I couldn't really fix for quartz was that the culet facets will always window out very easily, as they are just under its critical angle. It throws off the typical Asscher pavilion design to change it. But, if cut in beryl, you should be able to sneak by with no windowing. It's RI is just enough higher. The original windowed slightly, even in beryl.

 

[Richard M.]

Tony,

That''s great -- thanks for posting it. Those quartz designs sure get deep in a hurry don''t they?

Setting them can be an adventure. I recall a citrine barion I cut once and made a pendant setting for on commission. Trying to keep the setting design functional and from becoming klunky was quite a challenge. But the customer was very happy with the result.

 

[Proteus]

Richard,
No problem! Playing with optics is always an interesting endeavor. It certainly is deep at ~85% depth (ouch,) but that's the only way to avoid windowing in lower RI material. You could probably get away with shaving a degree or so off pavilion, and a few degrees off the crown, but it will still to window a bit once the culet facets drop under the critical angle. But, like you said, if everyone's happy in the end... I guess it's no big deal!

Let us know if you try it out for real -- it's always interesting to see how it looks once actually cut.

Moonwater, if we (hopefully) haven't scared you off will all this, you should be able to have a citrine custom cut with that pattern, as long as you don't mind the depth. The simulation images should give you an idea of what it might look like finished.

 

[Gailey]

Sorry, I''ve only just seen this post. Perhaps you may have been referring to my citrine asscher. It was cut by Peter Torraca, who sometimes posts here.

I just love it and would have done something with it by now, but I''m a professional gardener so my summers are kind of hectic.

I notice from gemologyonline.com that Peter has just cut another lovely golden yellow citrine, so maybe he has more of the rough available http://gemologyonline.com/Forum/phpBB2/viewtopic.php?t=3592&postdays=0&postorder=asc&start=765

He''s also got a pretty nice rubellite asscher on the same post.

Hope this helps in your quest!

 

[Gailey]

Here is a link to my post with more pictures. https://www.pricescope.com/community/threads/more-shots-of-gaileys-citrine-asscher.85533/

 

[MoonWater]

Thanks for the info Gailey. Does Peter have a site of his own with gems to purchase or do you need to email? I was actually leaning toward a ready made pendant I found. But of course this morning I started thinking of how cool it would be to have a nicely cut stone instead. Arrggh...back and forth. One is stress free, the other isn't. Since I have a wedding coming up and two trips to plan (in addition to classes and work full time), I'm leaning to the stress free option very strongly. Also I spoke with Jeff White who has the most gorgeous stones, but the quote was a bit more than I expected since he doesn't stock citrine. Throw in the cost for customizing a pendant for the stone and I would be over budget (which isn't good when you have a wedding coming up, right?!?)

*sigh*

ETA: Did you ever set your stone? I think what you will end up with is idealy what I would like to have as well. The most stressful part of this is that it's a gift so it's not like I can simply say "hey here's what *I* want" and be done with it.

again....*sigh*

 

[ptorraca]

A friend of mine clued me in to this thread -- sorry I didn''t catch it sooner, I lurk here when I get the chance, and chances have been few of late...

Moonwater -- I don''t wish to violate any local conventions on advertising, so I won''t post my contact info here. However, a quick google of my last name will find my personal blog with contact info. Oh, you may find my web-work from a previous life. I too learned HTML by using the good old "view source" function. That lead me to learn scripting, then databases, then config files for Apache servers... it was almost as slippery a slope as gemstones, but gems hooked me deeper.

Richard, Tony -- this is a really interesting conversation to me. I''ve also struggled with depth & tilt-windowing on Asscher-type stones in quartz. Only keeping the last tier small & reducing the tiers on the pavilion from 5 to 4 tiers (or even 3 on small stones) has helped.

Most people I show a quartz 4-tier Asscher to like them well enough. That fact & Tony''s renderings made me wonder -- is there really a face-up difference between the 4 tier Asscher and the 5 tier when it''s cut in quartz? Tony, any chance you could do a rendering of a 4 tier pavilion for comparison?

peter

 

[Proteus]

Peter,
Sure -- I can do some more renders with 3 and 4 step pavilions. I''ll post the results later today or tomorrow.

 

[Proteus]

Well, here''s the result. I re-rendered the 5-step pavilion version to make sure that the lighting was uniform... I couldn''t remember exactly how I had it setup the first time. I also made sure that each one was tilted at 8 degrees.

There doesn''t seem to be a huge visual difference in the number of steps, except that the 5-step has slightly more tilt brilliance, and the 3-step perhaps a little better face-up (at least around the crown facets.) Interestingly, the 5-step seems to deepen the color (it is a bit deeper overall, I believe) and the 3-step is lighter in color. The 4-step seems more or less intermediate between the two.

Also, there is much that can be adjusted in terms of where the steps begin and end with the facet arrangement, so I''m sure that plenty of other brilliance patterns are possible.

 

[ptorraca]

I can see why the 5 tier is preferred for diamonds. Having all of those tiers would really emphasize the dispersion. At the same time, I can''t see the point in doing all 5 tiers for quartz. The 4 and even the 3 tier look very good and it may shave off a little depth.

It seems that at 8* tilt, the 3 tier actually has an edge on the windowing effect. Very interesting.

I also noted that the 4 tier seems to have some two darker areas at the center (top center and right center) where the 5 tier is fairly even and the 3 tier has one darker area (right center). Does your software use the same lighting for each rendering?

Thanks, Tony!

peter

 

[Gailey]

Moonwater,
I haven''t set my stone yet. but have uploaded of a picture of what it might look like. I can''t remember where I found the picture, so if the owner of this lovely piece is reading, I hope you don''t mind. Although this is a ring, I am leaning towards a pendant because my asscher is quite deep at 8.97mm. That would make it sit quite high on my finger and knowing me I would be likely to take someone''s eye out!


Gentlemen cutters,
the conversation between you, whilst intriguing was a bit like rocket science to me. Perhaps you could explain in terms that us mere mortals can understand what is important when looking at gemstone asschers. For instance, your conversation centered around quartz, but how would that differ if, say we were talking about garnet or peridot etc?

 

[Proteus]

Peter,

Glad I was able to help out. I agree, it seems to be a waste of time to do all 5 steps on quartz, there just isn''t really enough refraction going on. On the other hand, I suppose it could be useful to deepen the color of a light aqua or other beryl, considering the depth issue.
The lighting is exactly the same in each rendering, but the lights are placed unevenly, to simulate natural light sources. This makes the renderings more accurate, but it also makes those dark zones appear here and there from the slight differences in angles, etc. -- it''s kind of hard to visualize, but they may not be that apparent in person, it all depends on where the light sources are. I find that in real life, all the subtle ambient light tends to make those darker areas a bit less apparent. This is always somewhat of an issue with computer generated renderings.

Gailey, sorry about all the geekspeak. I''ll try to explain for you:

All transparent materials have a refractive index (RI) - it''s the measure of the difference of the speed of light in the material versus air. It''s why when you put a straw in a glass of water, it appears to "bend" or break... it''s because light moves more slowly through water. Water is an RI of I think 1.3 or so. Quartz is 1.54, so it bends light a bit more than water. Peridot''s RI is 1.65-1.69. Garnet ranges a lot depending on the type, from about 1.73 (grossular) up to 1.88 (demantoid.) So, an Asscher would not have as many cutting issues in peridot or garnet.

Anyway, when light enters a gem, it refracts off the facets inside the gem depending on the angle that it entered at, and the angle of the facet that it meets up with. If the angle is above or below a certain amount, it will either pass straight through the gem, or reflect out the side. The threshold of when it will pass through, instead of refract, is called the critical angle. It varies depending on the RI of the gem, it''s a higher angle in quartz, so there is a narrower range of angles at which light will refract back up to your eye. In diamond (RI 2.42) the critical angle is quite low, so there is a very large range at which light can reflect back, this is why diamonds appear so brilliant. It is much harder for light to escape out of a diamond. If light passes straight through, you see a "window" or that pale, dull area seen around the center when the gem is tilted. If it reflects out the side, or never escapes, you tend to see a dark area, which is sometimes called "extinction."

So basically, since quartz has such a small range of refractivity, it poses a challenge for us faceters to cut certain designs for it. Asschers tend to have a wide range of angles, and quartz usually shows a window at the tip of the pavilion, because the angles of those facets are below the critical angle. Light passes right through them, rather than reflecting back up as it would in a diamond (or other, more refractive material.) So, we have to tweak the design to make it perform its best in whatever material we are cutting.

Sorry about the wordiness, but I hope this helps.

 

[MoonWater]

Date: 8/23/2008 9:40:10 PM
Author: ptorraca
A friend of mine clued me in to this thread -- sorry I didn't catch it sooner, I lurk here when I get the chance, and chances have been few of late...


Moonwater -- I don't wish to violate any local conventions on advertising, so I won't post my contact info here. However, a quick google of my last name will find my personal blog with contact info. Oh, you may find my web-work from a previous life. I too learned HTML by using the good old 'view source' function. That lead me to learn scripting, then databases, then config files for Apache servers... it was almost as slippery a slope as gemstones, but gems hooked me deeper.

peter

Thank you! I'm pretty certain I found you. However, I just found out that earrings are the way to go so a specially cut stone isn't needed...at the moment. I'm still plotting my RHR!

 

[MoonWater]

Date: 8/26/2008 11:01:09 AM
Author: Gailey
Moonwater,

I haven''t set my stone yet. but have uploaded of a picture of what it might look like. I can''t remember where I found the picture, so if the owner of this lovely piece is reading, I hope you don''t mind. Although this is a ring, I am leaning towards a pendant because my asscher is quite deep at 8.97mm. That would make it sit quite high on my finger and knowing me I would be likely to take someone''s eye out!

Gailey that''s gorgeous! God I sooo want an asscher citrine! Be sure to post lots of pics after you set!

Gentlemen cutters,

the conversation between you, whilst intriguing was a bit like rocket science to me. Perhaps you could explain in terms that us mere mortals can understand what is important when looking at gemstone asschers. For instance, your conversation centered around quartz, but how would that differ if, say we were talking about garnet or peridot etc?

LOL, I was thinking the same thing. But I like the pretty pictures.