Extinction

[mellowyellowgirl]

Hi Folks

I need education on extinction.

Lately I am not sure if what I am calling extinction is extinction.

When the colouring is even in a stone but you still see a lighter patch and a darker patch depending on how you tilt it, is that called extinction?

I took some random stones off the internet. Which of these is called extinction?

 

[Rfisher]

Cure for the half/half!?

I don't have one. Maybe you do. It steals half of our ovals and rectangular stones. Call it half/half extinction, shadowing, or a light and dark effect. Whatever you call it, you will usually preface it with an expletive. As many on this forum know, some stones (only ovals and rectangles to...

www.pricescope.com

Blue sapphires with no half/half extinction?

Let's settle the half/half extinction debate once and for all. Is there really such a thing as a sapphire without it? Let's prove it on this thread! I've been following the postings on the colored stones forum and I've seen quite a bit of discussion over half/half extinction. I'm looking...

www.pricescope.com

Extinction

This is a common topic in the colored stone world. I just read many of the threads here, inspired by an article Richard Hughes wrote for the australian jewellery valuers mag, and sadly, it seems that few colored stone people understand the cause of extinction- it is the viewers head and body (or...

www.pricescope.com

Plenty of threads for interesting info/opinions if you wish to search for more, my apologies if you already have. Bringing the subject back up isn’t a bad thing though

I don’t think stone 2 and 3 you show are extinction. Bow tie. Someone else will correct me if I’m wrong-ha!

 

[mellowyellowgirl]

Ahh thank you so much @Rad_Fan

I did do a search I swear! It just didn't pop up!

Don't like the bow tie either! Will read about that too!

 

[icy_jade]

This is a great article imo:

Brilliance, Windows, and Extinction in Gemstones • Lotus Gemology

Lotus Gemology's guide to how gemstone quality is impacted by brilliance, windows, and extinction.

www.lotusgemology.com

I like the use of diagrams to explain the technical aspects

 

[voce]

From the experts' words: "Extinction is black, with none of the hue of the stone apparent." (Lotus Gemology article)

Technically, only the fourth stone is extinction. I can see the hues in the shadowed areas in the first three.

 

[mellowyellowgirl]

From the experts' words: "Extinction is black, with none of the hue of the stone apparent." (Lotus Gemology article)

Technically, only the fourth stone is extinction. I can see the hues in the shadowed areas in the first three.

Is there a name for the patchiness?

Just uneven colouring? I've seen videos where 3/4 of a stone is a different shade due to the way the light is hitting it and it puts me right off.

I'd like to identify the term for that too!

 

[icy_jade]

i would consider all 4 to have extinction?

Guessing wonky bottoms from how they look

 

[voce]

Is there a name for the patchiness?

Just uneven colouring? I've seen videos where 3/4 of a stone is a different shade due to the way the light is hitting it and it puts me right off.

I'd like to identify the term for that too!

I'd call it shadowing, but I think it's more precise to refer to the complement, i.e. the percent brilliance of a gem. Estimate what percent area you do see a vibrant color for, and the higher the percent, the better.

These are my estimates, for example:
1) 40-45% brilliant
2) 75-80%
3) 75-80%
4) 25-30%

Obviously, any gem with less than 50% brilliance is not worth your time, unless they're unicorns.

 

[Rose-gold-or-bust]

Cure for the half/half!?

I don't have one. Maybe you do. It steals half of our ovals and rectangular stones. Call it half/half extinction, shadowing, or a light and dark effect. Whatever you call it, you will usually preface it with an expletive. As many on this forum know, some stones (only ovals and rectangles to...

www.pricescope.com

Blue sapphires with no half/half extinction?

Let's settle the half/half extinction debate once and for all. Is there really such a thing as a sapphire without it? Let's prove it on this thread! I've been following the postings on the colored stones forum and I've seen quite a bit of discussion over half/half extinction. I'm looking...

www.pricescope.com

Extinction

This is a common topic in the colored stone world. I just read many of the threads here, inspired by an article Richard Hughes wrote for the australian jewellery valuers mag, and sadly, it seems that few colored stone people understand the cause of extinction- it is the viewers head and body (or...

www.pricescope.com

Plenty of threads for interesting info/opinions if you wish to search for more, my apologies if you already have. Bringing the subject back up isn’t a bad thing though

I don’t think stone 2 and 3 you show are extinction. Bow tie. Someone else will correct me if I’m wrong-ha!

The search feature here really sucks. You can type in the exact title of some threads and never get it to show up when you search for it

 

[PieAreSquared]

The only place I have ever heard the term "half and half extinction" is here on PS.

It is most definitely shadowing, and as has been brought out before, you will only see it on elongated shapes like ovals and rectangles because of the way light is reflected back unevenly.
Setting East-West sometimes helps, but personally I can't stand it and don't own any ovals because of it.
True extinction is another thing completely, it won't matter how you turn the stone, it will still have dead spots.
None of the 4 stones appear to have extinction, the 1st and 4th have the shadowing, the 2nd and 3rd have bowties.

 

[T L]

Elongated cuts like ovals and radiants typically have what I call “half ‘n half” extinction if they’re dark enough. That means that when you tilt the stone, half of it becomes much darker in tone. There is also the dreaded “bow tie” extinction you see in other elongated cuts like marquise and pear shapes. Your second oval picture clearly has a bow tie. My favorite spinel can get darker in tone on one half, but it’s not so dark that it totally blacks out.

 

[voce]

It is most definitely shadowing, and as has been brought out before, you will only see it on elongated shapes like ovals and rectangles because of the way light is reflected back unevenly.

I disagree with the claim that you will ONLY see shadowing on elongated shapes, as the square cushion ruby in my avatar definitely shows shadowing as well.

Although most elongated shapes will have the half and half effect or a bowtie, other factors come into play besides the stone orientation: differences in camera, lighting (including direction of light reflecting too the eye or camera), silk, and the setting style.

For reference, here is my ruby engagement ring. You see the shadowing in some pictures but not others.



Weak sunlight outdoors in Toronto. Here you see the difference with N-S vs E-W stone orientation.


Diffused natural light indoors: no shadowing apparent, which I presume is due to the silk.


When the sun is rising or setting, I see no shadowing because the direction of the light hitting the gem is different.

 

[T L]

Strong fluorescence as in rubies and red spinels also helps to extinguish some extinction in elongated cuts in sunlight.

 

[PieAreSquared]

As soon as I hit 'Post Reply', I knew someone would call me out on the use of "only" @voce, but I was in a hurry this morning with no time to modify. Let me soften that dogmatic statement to "Most often" shadowing is exhibited on elongated shapes...

Still, it's not EXTINCTION in the gemological sense of the word, half n half or otherwise. For a while here on PS we were using the term "half and half shadowing" which is far more accurate IMHO.

One more thing to mention is that true extinction would be next to impossible to identify in a still photo. Turn that #4 stone the opposite way and I will bet the shadow falls on the other side.

 

[voce]

One more thing to mention is that true extinction would be next to impossible to identify in a still photo.

So true . So many PSers, myself included, like to throw this word around when we've only been presented with still photos. We should strive to use the term correctly (thus sparingly).

 

[T L]

We’ve been calling it “half ‘n half extinction” in this forum for years. I’m not sure of the true gemologal term, but I know the supernova oval cut was developed to reduce that phenomena. Whatever it’s called, it can be a bothersome visual attribute.

I had a radiant cut by a very well known and beloved lapidary/gemstone dealer on this forum, and he ruined an otherwise nice tourmaline with a radiant cut and a keel cutlet. The half n half trait was so prevent, it was impossible to enjoy the stone!!! I sold it, just awful.

Even the best lapidaries sometimes make mistakes!!!

 

[PieAreSquared]

We’ve been calling it “half ‘n half extinction” in this forum for years. I’m not sure of the true gemologal term, but I know the supernova oval cut was developed to reduce that phenomena. Whatever it’s called, it can be a bothersome visual attribute.

Agreed, it is not attractive.
I don't think there actually is a gemological term for shadowing, since it is not technically a "flaw", and the prominence (or lack of) it depends greatly on the direction of and source of light.

Associating the term "extinction" in any form with this phenomena, however, is still inaccurate, no matter how many years it has been inappropriately used.
Extinction is a completely different issue, and throwing the word around loosely does a great disservice to anyone who comes on this forum trying to educate themselves and make an informed decision.
Personally, I'll stick with calling it "half and half shadowing" to avoid confusion.

 

[T L]

Based on this excerpt from Lotus gemology’s website

“The American Gem Market System (AGMS) Network Grading Manual (1986) had this to add about extinction:
"Extinction," or "blackout" in gem materials is a phenomenon most apparent in dark tone stones, but which can be present in lighter tone material also. The effect can be reduced in the middle of the stone by "windowing" during cutting. Orientation of rough during cutting can either decrease or increase the effect, but cannot entirely eliminate it unless the stone is cut too shallow or with almost no BRILLIANCE. When grading extinction, the stone is held face up over a plain white background under diffused daylight lighting, and a judgment is made as to how much (what percentage) of the stone reflects back the true color of the gem and does not "black out." The visible surface of the stone represents 100%. When the stone is tilted slightly in any direction, any extinction present will appear to move from facet to facet. The percentage of the stone which is "extinct" usually remains constant, so an estimation can be made as to what percent of the total area is extinctive. Care should be taken not to confuse dark tone with extinction. Extinction is black, with none of the hue of the stone apparent.”


I read that to mean that perhaps, some, not all of the half ‘n half phenomena, can be extinction if that half of the stone goes black. As I recall, although the aforementioned tourmaline I had was medium light in tone, when I tilted it, the other half was black or nearly so.

I agree that dark tone should not be confused with extinction. Heavy extinction Is more a property of poor cutting, however based on the above, it is more prevalent in darker toned stones.

 

[voce]

Based on this excerpt from Lotus gemology’s website

“The American Gem Market System (AGMS) Network Grading Manual (1986) had this to add about extinction:
"Extinction," or "blackout" in gem materials is a phenomenon most apparent in dark tone stones, but which can be present in lighter tone material also. The effect can be reduced in the middle of the stone by "windowing" during cutting. Orientation of rough during cutting can either decrease or increase the effect, but cannot entirely eliminate it unless the stone is cut too shallow or with almost no BRILLIANCE. When grading extinction, the stone is held face up over a plain white background under diffused daylight lighting, and a judgment is made as to how much (what percentage) of the stone reflects back the true color of the gem and does not "black out." The visible surface of the stone represents 100%. ”

I think we should talk about % brilliance instead of extinction. This is more in line with how gem labs (AGL, Lotus) evaluate stones, too, anyway.

 

[deorwine]

Based on this excerpt from Lotus gemology’s website

“The American Gem Market System (AGMS) Network Grading Manual (1986) had this to add about extinction:
"Extinction," or "blackout" in gem materials is a phenomenon most apparent in dark tone stones, but which can be present in lighter tone material also. The effect can be reduced in the middle of the stone by "windowing" during cutting. Orientation of rough during cutting can either decrease or increase the effect, but cannot entirely eliminate it unless the stone is cut too shallow or with almost no BRILLIANCE. When grading extinction, the stone is held face up over a plain white background under diffused daylight lighting, and a judgment is made as to how much (what percentage) of the stone reflects back the true color of the gem and does not "black out." The visible surface of the stone represents 100%. When the stone is tilted slightly in any direction, any extinction present will appear to move from facet to facet. The percentage of the stone which is "extinct" usually remains constant, so an estimation can be made as to what percent of the total area is extinctive. Care should be taken not to confuse dark tone with extinction. Extinction is black, with none of the hue of the stone apparent.”


I read that to mean that perhaps, some, not all of the half ‘n half phenomena, can be extinction if that half of the stone goes black. As I recall, although the aforementioned tourmaline I had was medium light in tone, when I tilted it, the other half was black or nearly so.

I agree that dark tone should not be confused with extinction. Heavy extinction Is more a property of poor cutting, however based on the above, it is more prevalent in darker toned stones.

I don't think this quote can be taken to mean half-and-half = extinction, because it specifies diffused daylight lighting.

I have a lot of oval gems (and, uh, have bought more and returned them), and they often display half-and-half shadowing, but this is almost always in situations where it is not diffused lighting, but rather point-source lighting (the sun, or a bright light). When I put these gems in diffused lighting they generally do not display this kind of effect.

 

[deorwine]

Still having problems with my camera but here are a couple of pics I took of a gorgeous sapphire earlier in the year (that I ended up returning and someone else has now bought it, but it was really beautiful) that demonstrates this. Oval shape, displays a whole heck of a lot of half-and-half shadowing in direct light (and in some shaded conditions that I postulate are more like direct light).



But in diffuse lighting it doesn't appear to have much extinction at all: