Extinction in static photo - isnt it difficult to judge objectively?

[haagen_dazs]

Hi all
I read about the caution to buy gemstones that do not have extinction.
However in a static photo where a stone may have some dark regions, isnt it harsh to say that those gemstones have extinction?

I read some threads where people comment that the stone has extinctions due to dark shadows in the stone in a single photo online.

Isn''t some obstruction or extinction a good thing as that helps in the patterning and contrast department ? (just like the arrows in a diamond when viewed face up)

 

[LD]

I'm not an expert but from buying coloured gemstones (which are a different animal to diamonds) it's all about colour. If a gemstone is cut and has extinction it blacks out the colour. Therefore not a good thing. Some gemstones have extinction BUT overall are lively and therefore can be forgiven but it's a personal thing. Some people won't accept any extinction. I will accept a small amount IF overall the gemstone's beauty isn't compromised and the gemstone is still beautiful and shows colour.

Edit: You may find this interesting. http://www.ruby-sapphire.com/brilliance_windows_extinction.htm

 

[packrat]

I think that''s why it''s qualified with "might". It is hard to tell just from a picture what a gem is going to look like. This is of course coming from my super vast knowledge and experience..of my 3 whole gems hahahahaha! However, my spinel, in the vendor pictures had black areas, and I almost didn''t even ask to have it sent to look at in person. I was told by the other CS''ers that it "could" be extinction, but the only way to tell was to see it myself, and ask the vendor.

I figured extinction would be to colored gems what a big black carbon spots would be to a diamond.

 

[cellentani]

I think extinction and obstruction are two different things. Obstruction, say from a camera blocking the light, can bring out the scintillation pattern so you can see arrows, and I would never think of that as extinction.

 

[chrono]

Absolutely: extinction and head obstruction are completely different.
Extinction is bad = huge black areas where you can't see much colour. This usually due to bad cutting or poor cutting design selected for the material.
Head obstruction = shadow cast on the stone by YOUR head or camera as you peer too closely to the stone.
Scintillation = even spaced light and dark areas thoughout the stone to give it some liveliness. These dark and light areas are small; far smaller than the dark areas of extinction.

Sometimes, small areas of extinction are fine but definitely not huge blackout patches.

 

[haagen_dazs]

thank you all for your inputs!
this is very useful to know

 

[ma re]

If it''s comprised of regularly shaped patterns, to me it''s not extinction, cause extinction is a flaw produced by a lousy cutting job (or rough material restrictions). But it also depends on the type of material. For instance, most colored stones will show some extinction, but some materials like fine sapphires, rubies etc., will get a help from microscopic inclusions plus a very saturated color and/or fluorescence to mask it. On THIS page you can see rubies with heavy extinction, those with minor to moderate, and those where clarity is reduced to such a degree that extinction isn''t even possible - also not a good thing.

 

[haagen_dazs]

is this extinction ?
link

 

[haagen_dazs]

how about this one ??? link
as the gems turn 360, i can still see the black zones...

if it is NOT extinction, the black zones would disappear at different viewing angles right?

 

[LD]

Most coloured gemstones show lightness/darkness. The link you've posted (the first one) shows some (a small amount) of extinction but overall the gem is bright. If I were considering that gemstone, it wouldn't worry me. Don't forget, when the stone moves you see other facets so the extinction can disappear but doesn't always. You have to decide how much extinction YOU can put up with before it detracts from the beauty of the gemstone.

Look at this gemstone. It's an Umbalite Garnet. You can see that it has some extinction (quite a bit) BUT this gem is so bright that you focus on the colour not on the black bits.

Edit: The second link with the Spinels? They're lovely and well cut. They're a tad too dark for my taste but I wouldn't say that they're showing extinction. Don't get confused between the lightness/darkness when the stone moves and extinction. Darker gemstones will show this much more than lighter ones.

 

[Michael_E]

Date: 11/7/2009 2:28:41 PM
Author: haagen_dazs
is this extinction ?

No, that''s an image of the photographers head, camera and upper body. You can not tell from a picture if you are looking at extinction or something dark that''s being reflected by the pavilion of the stone, (except for light toned stones like this one, which will never show areas this dark from extinction). If you have the stone in hand it''s much easier, because head shadow will shrink and disappear as you move the stone away from you. The dark areas from extinction will not change as you move the stone away from you. Both causes of darkness will change as you rotate the stone, so it''s still a guess when looking at rotating video clips, (except for tourmaline which will blink on and off if they have a dark "C" axis).