demantoid vs. tasvorite

[velouriaL]

Hest''s posts have really whet my appetite for something green...
So I was wondering about Demantoids and Tsavorites..
What is the difference, really?

This is what I''ve learned so far-
                  Demantoid                Tsavorite
Location      Russia                        Kenya
Coloring      chromium                  vanadium, chromium
Clarity          Signature Horsetail    should be clean
hardness      6.5 to 7                      7 to 7.5
dispersion    0.057 (WAY sparkly)  0.028 (not sure what that means)

So... what I''m gathering is that, average gem lover, both the D and T can be about the same color (deep "emerald" green in their ideal form), the D has a signature inclusion and the T does not.  The D is really sparly and the T is a bit more muted... but the T is harder and more durable.

Any other points of comparison?

Tsavorites

Demantoids

 

[raddygast]

Good questions. I was just about to post on this too. Dispersion has to do with splitting up light into its component spectrum, due to having a bigger discrepancy in RI for the different wavelengths, right? What I don''t understand is how this can possibly apply to a colored gem that absorbs light except at a given wavelength.

And here''s another question. Do gems let through various wavelengths of light (i.e. say a slpR ruby would let through some violet wavelength and some red wavelength), or do they let through one basic wavelength/color (if there is no zoning) which somehow captures the mix of the two pure colors? The spectral colors are just arbitrary wavelengths, aren''t they? All the in-between stuff probably has a wavelength too.

Anyway, I obviously don''t understand additive color theory and optics very well at all. Just thought I''d really find out what dispersion means for a gem. More "fire". But what about brilliance?

The RI for garnets is not very high, is it? Isn''t that what makes diamond so amazingly flashy?

Finally, is the "ideal" color for T and D garnet the same?

 

[velouriaL]

Exactly!

Anyone, anyone?

 

[raddygast]

bumping this because I''m quite surprised nobody has replied.

 

[valeria101]

Date: 1/27/2005 7:57:21 PM
Author: raddygast

The RI for garnets is not very high, is it?

Finally, is the 'ideal' color for T and D garnet the same?

Garnet and sapphire are about as brilliant - although not all garnets go in the same pot. Demantoid is quite a bit more brilliant than the rest of garnets. It also has high dispersion - which both the other garnets and sapphire lack. Dispersion is not necesarily a function of RI (at least not among gems, I think they are functionally related for fluids).

Anyway, my gut feeling says that yelowish overtone is expected and tollerated more for demantoid and lighter tone desired because it shows brilliance and fire better. Richard Wise's book spells these things out way clearer than I could.

'Guess it is a matter of personal judgement how narrow these "ideals" are. As far as I remember from the story of your spinel hunt, you started with a very, very narrow definition and relented because the desired item just wasn't there. What's the use to define some ideal color if there are just a couple of such items and more often than not none available at all ? Demantoid was just not there for quite a long time... Top color tsavorite is not very common either and large stones pretty darn rare to classify. Not that it doesn't make sense to develop a strict quality scale - it does just as much as developing the phylogeny of dinosaurs extrapolating from three teeth per species

 

[raddygast]

You have a good point, but I should mention that I had to extend my color parameters in spinel not only due to rarity and the availability being limited, but also budget.

I think that pure, perfect, ultra-red spinel *is* available, though exceedingly scarce and you have to know the right people in the right circles to have a crack at owning one. But what I was looking for clearly did not fit my budget, and yes, it did take me a long time to figure that out. Part of the problem is the rapid changes in a market that is so focused and specialized, so that a lot of the "advice" and info on the internet was woefully out of date with price estimations and realism.

That said what I did find ended up being a fantastic deal and very very close to what I wanted. But that brings up a second point. Sometimes you end up with something that is not quite that "ideal" but you end up liking as much, or in my case better. In that case, shooting for the ideal can be said to have helped the end result. Reach for the stars, and what you end up grasping will be beyond what you might have done if you had lowered your standards.

I am sure this applies to demantoid as well. In fact, I see a lot of parallels between spinel and demantoid, except demantoid is perhaps even rarer and just back on the market with a trickle. (this may have been true for Mogok goods, too, since the flow of goods from Burma were nonexistent for a while, apparently in the 80''s).

 

[raddygast]

Another parallel: isn''t it said that tsavorite is untreated, and no enhancement for color has yet been discovered, much the same as spinel?

 

[valeria101]

Date: 1/30/2005 12:33:45 PM
Author: raddygast

Sometimes you end up with something that is not quite that ''ideal'' but you end up liking as much, or in my case better. In that case, shooting for the ideal can be said to have helped the end result. Reach for the stars, and what you end up grasping will be beyond what you might have done if you had lowered your standards.

Yes sir! I honestly admire your posts: yours is one crystal clear account for how colored gem-dependence sets in

I wish there was a way to bring your posts forth as refference on the forum. Perhaps Leonid would consider a "Colored Gems FAQ" now that there is an ice breaker

 

[valeria101]

Date: 1/30/2005 12:356 PM
Author: raddygast
Another parallel: isn''t it said that tsavorite is untreated, and no enhancement for color has yet been discovered, much the same as spinel?

Demantoid is not usually treated either (since no one claims to discern heating and the jury is out if it eve works...). Spinel might be treated to improve clarity although it may take a while to find such a thing.

I have no idea if any other garnet is ever, ever treated in any way. This doesn''t mean they are not, however.

 

[chantal990]

I thought for demantoid garnet horsetail inclusions were vauled. If you were to clarity treat them how would you keep the horsetails and get rid of the "crap"?(sorry couldn''t think of a better word too caffine depraved).

Personal preference is for tsavorite but that is probably because I have never really seen a fantasic demantoid garnet where as I have seen (and am lucky enough to own) a few really, really nice tsavorites.

 

[Hest88]

Date: 1/30/2005 11:22:45 PM
Author: Emeraldgirl
I thought for demantoid garnet horsetail inclusions were vauled. If you were to clarity treat them how would you keep the horsetails and get rid of the ''crap''?

They''re actually talking about heat treatment to improve the color, and not clarity enhancement.

Incidentally, if the Pala databases means anything, it looks like more of the newer demantoids are being heat treated than previously. That oval I was going to buy was heat treated.

Also, this might interest you: when I was talking to Josh at Pala, he told me that there was a tendency for there to be less fire with the bright, evenly-colored dems--such as the oval--than with the more unevenly colored dems (such as my original cushion). Interesting, huh? So you actually might have to make a trade-off between the color and the coveted dispersive effect.

 

[Richard M.]

Date: 1/31/2005 12:36:48 AM
Author: Hest88

Date: 1/30/2005 11:22:45 PM

he told me that there was a tendency for there to be less fire with the bright, evenly-colored dems--such as the oval--than with the more unevenly colored dems (such as my original cushion). Interesting, huh? So you actually might have to make a trade-off between the color and the coveted dispersive effect.

I wanted to write more on this and the spinel thread but I''m rushing to catch a plane for Tucson and I just lost my first draft to a computer glitch. Grrrrr!!

I don''t know what Josh was specifically referring to but as the green color of andradite intensifies the the ultra-strong dispersion diminishes. I have several matched pairs of beautiful intense green demantoids (demantoid is the green hue of andradite) and while the color is sweet, luminous and all-around magnificent, there''s very little dispersion visible.

As the hue lightens into the yellow-greens, greenish-yellows,and yellows of andradite (sometimes called topazolite), the light show from dispersion is reminiscent of sphene and a few other higher-than-diamond dispersion gems. Demantoid takes its name from the Dutch word for diamond, "demant."

Demantoid is notable mainly for its gorgeous colors and "horsetail" byssolite inclusions while the andradite hues are prized for dispersion. Some dealers play the pink sapphire/ruby game and call all andradites "demantoid." Just as rubies are red, demantoids are green. But who can say where the borderline is? Demantoids are now being produced in Namibia and from a new source in Iran. I''m told that Namibian stones often don''t always have byssolite and I hope to study them closely in Tucson.

Some of you may be interested in a brief garnet article I''ve written for "Lapidary World," a new on-line "magazine" edited by my colleague Hans Durstling. It''s one in a series I''m writing for the website I''m developing. Unfortunately the great images I sent with it haven''t shown up yet. Anyhow you can read it, see the world''s largest carved black opal and read several other articles by my friends and associates at: Lapidary World

 

[Hest88]

Date: 1/31/2005 2

5:16 AM
Author: Richard M.

I don''t know what Josh was specifically referring to but as the green color of andradite intensifies the the ultra-strong dispersion diminishes

Have a good time in Tucson!

I think that''s basically what he meant. In other words, I was just used to thinking of the dispersive effect of any stone diminishing when the color was darker--just purely because the darker colors masked the light return effect--when he told me that in andradites a darker stone can be more dispersive if the lighter stone just has a more intense color.

 

[velouriaL]

This is fascinating!

What other colors do andradites come in? I would love to see pictures of the "''aurora rose''-colored gem" that Richard speaks of in the article. I''m imagining a pad-color blinger with a light show and drooooling...

 

[valeria101]

Date: 1/31/2005 11:50:13 AM
Author: velouriaL

What other colors do andradites come in ?

Color like color: between rust and green of any tone imaginable, but not very intense... but the largest "topazolite" I know is barely one carat

There must be better, just never crossed my way !


This... is some other sort of garnet. If any garnet might fit the color description you mention ("peach" if not "pad" whatever the difference)... this must be it though

(source: R.W.Wise Goldsmiths)