Cure for the half/half!?

[corundum_conundrum]

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 my knowledge in any pronounced way) will show "shadowing." That is, in all but the most perfect lighting and viewing-angles, the stone can only show top color in one of its halves. The other half will go black or dark.




Many threads have devolved into arguments about what causes this effect, or whether it is really so bad. My concern is not to evaluate the phenomena or identify causes, but to find solutions. It seems to be a particuarly troubling phenomena, in that unlike windowing, it can't always be detected in pictures. Nor will buying a stone precision cut by a recommend cutter always guarantee that the effect will not be present. Precision cut stones posted on this forum have confirmed that such stones are susceptible to shadowing. So how can the consumer avoid stones with shadowing if they so wish?

I believe that answers to the following questions should help the shadow-averse buyer:

1. Is there an accepted trade term for this effect? Some cutters object that "half/half extinction" is not true extinction given that it can't be seen at a perfect vantage point, and therefore should not be called extinction. So it would help consumers if they knew the trade term in order to ask vendors whether stones they are interested in exhibit it.

2. Will certain cuts preclude the shadowing? There are rumors on this forum that certain types of cuts will prevent shadowing. Supernovas and concave faceting are most often cited as impervious to shadowing. Some mention Barions. More minor cutting adjustments are also mentioned: a keel-type cutlet or a smaller table are said to prevent it. If its true that any of these cuts or variations will eliminate the effect, than the shadow-averse can feel safer buying such cuts, or request them when ordering a custom stone. Also, radiant emeralds are cited as particularly prone to the effect. Are these rumors true?

Knowing the answer to these might provide buyers with ways of avoiding shadowed stones--without having to just buy and check nice ovals and rectangles.

 

[chrono]

I'm doing a post & run this morning but I've seen non precision cut stones also show the half lit and half dark characteristic. IIRC, I once owned a precision cut Barion design stone showing this egfect too. One way to not see this is to rotate the stone 90 degrees from when you do see it. Meaning, it is is side to side, rotate it North South. If it is up / down, rotate it lengthwise to East West and this effect is no longer seen.

 

[LD]

At the end of the day this phenomena is caused by the cut. It can happen in precision and non-precision cut stones.

There is no "cure".

 

[minousbijoux]

Yes. The solution is to look at the stone before you buy and buy one devoid of the phenomenon. Not all stones have it.

Sorry to be brief, but I feel like we've talked this to death already.

 

[corundum_conundrum]

Yes. The solution is to look at the stone before you buy and buy one devoid of the phenomenon. Not all stones have it.

Sorry to be brief, but I feel like we've talked this to death already.

haha, okay. Sorry to beat a dead horse.

I made this post because I searched through old threads trying to find more information about shadowing. Specific cuts are casually mentioned as resistant to shadowing, but it is never discussed in detail. I for one would be very curious to know if any of those claims are true. Its all fine and well to order a stone hoping that it doesn't have shadowing, but if you knew in advance that it was unlikely that the stone had shadowing because it had a certain cut, that would save time and money in reshipping. Chrono confirms that Barion cuts will not prevent it (thanks!). Any others think Concave cuts, supernovas, small tables or keel-cutlets are definite ways to avoid shadowing? If so, I would rest easy buying stones with such cutting.

Also, unlike bowties, I've seen no cutting articles dedicated to this subject. Does anyone have a link to one?

I was being a bit cheeky with the titlle of this post. I'm not looking for a "cure" as much as reliable ways to avoid buying these stones (other than just taking a gamble on them). I am happy to have a link to another thread where the trade-accepted term for the effect is discussed, or where the specific cuts I mentioned are evaluated as to whether they never show shadowing.

 

[minousbijoux]

In all seriousness, I ask the vendor in advance. There are very few occasions when the vendor has told me it didn't have it when in actuality it did. It is less frequent with barion cuts and supernovas, but I would still ask the question of the vendor regardless. I find that the effect is less bothersome to me on lighter colored stones as well - if its there, then the stone will read as having color, instead of more pronounced extinction of darker tones. That is while it doesn't eliminate the phenomenon, I can enjoy the color if I choose to keep it.

I think it is isolated to elongated cuts, as I don't remember ever seeing it on rounds, asschers and square cushions, princess, trillions, etc.

 

[LD]

Reliable ways to avoid it? None.

You may see it, others won't.

People have posted pictures where it has been incredibly obvious and others don't see it. The only way to avoid it is to look at as many photos as you can before you buy, ask questions and then send it back if you get it and it's not what you want.

I know this sounds dreadfully simple but it is. There's no magic formula to buying coloured gemstones (unlike diamonds). It's not as simple as looking for a specific cut, avoiding Y cut, buying X cut etc. This really is about developing your eye and learning by experience.

Oh and by the way, in some gemstones it can be the best thing ever. If you've found old threads you'll have seen a precision cut Umba Garnet I own cut by Gene and it's one of the most beautiful stones with a personality I own. If I were avoiding the "half/half" look I'd have missed out on it and some other lucky person would have benefitted from my stupidity!!!!

 

[corundum_conundrum]

Yes LD; that Umba Garnet is spectacular. The shadowing seems to make it look two-toned, and both tones are beautiful. However, I think this is the exception rather than the norm. Most of the time shadowing makes one side of the stone look pretty dull, IMO.

Good to get your method, Minous. Asking vendors is a must, but it would be nice if there were some universal term for the effect like there is with windowing to make it easier to ask about. Its comforting to know that Barions and Supernovas are somewhat resistant to half/half in your experience. Although I do wonder whether there is a correlation-not-causation phenomena happening here (that is, we see fewer supernovas and barions, and they lack shadowing, so we think the specific cuts are causing the lack of shadowing, when it is really just coincidence with the specific cut).

 

[minousbijoux]

I honestly don't know whether it needs to be analyzed. I think you can ask vendors in a way they understand. Does the stone have any extinction? Does it appear to the eye to be consistent in color? Is there any shadowing? How is the light performance? Those are the type of questions I ask and then, if I'm still concerned, I ask for a hand shot in various lighting. Some vendors aren't willing to help out and then I decide whether to get the stone and take the chance of returning it, or not.

Really, I think that's all you really can do...

 

[corundum_conundrum]

I suppose your pragmatism always prevails Minous: the more questions you ask and the more ways you phrase the question, the better your odds are at getting the full scoop. I suppose I will use all the phrases when asking (ie "does the stone exhibit shadowing/light and dark/half-and-half extinction when your vantage point is not directly perpendicular to the table?" "Does it make one side just a shade darker, or does it really occlude half of the stone" ).

Still, it is interesting that the status quo is that certain optical drawbacks (ie windows) are almost always disclosed by PS vendors. I think we would find it less-than-forthright if a PS recommended cutter did not disclose in a description of the gem that it had a window. And yet, it seems that we have to probe a vendor or order a stone only to find that it has shadowing. It is sad to me when an excited PSer orders a precision cut stone, only to find that it shadows so severely that they have to return it (as I have seen happen on this board). If they are armed with the right questions, they can ferret it out before buying, but it seems it would be preferable if shadowing was disclosed like windows. Granted, shadowing can be more or less of a drawback depending on the stone, but so can windows. "Minor shadowing" would be helpful disclosure.

Back to cutting: So its possible Barions/Supernovas/concave faceting can be good bets if one wants to avoid shadowing, although they are no guarantee. How about a small table or keel-type cutlet? Conversely, are radiant emerald cuts generally to be viewed with more skepticism? That is, is that cut MORE prone to shadowing? I was kind of hoping for a magic buller, but it looks liek the magic bullet is just rounds or squares...

 

[minousbijoux]

Oh, sorry if I wasn't clear! When I was talking about spelling it out in different ways in that manner, it was for non-native speaking ebay vendors. I believe that if I were to ask any vendor on the PS list, they would be forthright and honest. If, after asking, you do not receive an indication that it has that 1/2 and 1/2, and IRL it does, I would return it and indicate why. Then if you are comfortable doing so, I would hope that you'd come here and let us know...

 

[LD]

I suppose your pragmatism always prevails Minous: the more questions you ask and the more ways you phrase the question, the better your odds are at getting the full scoop. I suppose I will use all the phrases when asking (ie "does the stone exhibit shadowing/light and dark/half-and-half extinction when your vantage point is not directly perpendicular to the table?" "Does it make one side just a shade darker, or does it really occlude half of the stone" ).

Still, it is interesting that the status quo is that certain optical drawbacks (ie windows) are almost always disclosed by PS vendors. I think we would find it less-than-forthright if a PS recommended cutter did not disclose in a description of the gem that it had a window. And yet, it seems that we have to probe a vendor or order a stone only to find that it has shadowing. It is sad to me when an excited PSer orders a precision cut stone, only to find that it shadows so severely that they have to return it (as I have seen happen on this board). If they are armed with the right questions, they can ferret it out before buying, but it seems it would be preferable if shadowing was disclosed like windows. Granted, shadowing can be more or less of a drawback depending on the stone, but so can windows. "Minor shadowing" would be helpful disclosure.

Back to cutting: So its possible Barions/Supernovas/concave faceting can be good bets if one wants to avoid shadowing, although they are no guarantee. How about a small table or keel-type cutlet? Conversely, are radiant emerald cuts generally to be viewed with more skepticism? That is, is that cut MORE prone to shadowing? I was kind of hoping for a magic buller, but it looks liek the magic bullet is just rounds or squares...

Where did you get that from? That's absolutely not true.

When a stone is rotated, the gem may not show the half/half. I can take photos of my stone from Gene that categorically DON'T show any half/half. I don't manipulate the photo, it's just that sometimes it really doesn't show it.

Let's be real for a minute. Look at Tiffany's website. Do they declare treatments on their gemstones? No. If you buy a second hand car from a dealer do they point out all the cars faults or do they tell you about the good points? Why would you ask a gemstone dealer to list the flaw of every stone (a flaw YOU may see as a flaw and others don't)?

Here's a really good example http://www.rwwise.com/products/id%7C255 The blurb clearly says this is a beautiful stone. Where does it say about the off centre culet? I can pick tons more examples but this illustrates my point well.

At the end of the day, coloured gemstones are generally prized not for their cut but for their uniqueness.

 

[corundum_conundrum]

Hi Minous. I may have misunderstood you, but I still don't think its such a bad idea to spell-out in a couple of different ways what one is a worried about to a vendor. Particularly because there is no standard term for this phenomena, and some cutters patently object to calling it extinction.

Still, it is interesting that the status quo is that certain optical drawbacks (ie windows) are almost always disclosed by PS vendors. I think we would find it less-than-forthright if a PS recommended cutter did not disclose in a description of the gem that it had a window

Where did you get that from? That's absolutely not true.

When a stone is rotated, the gem may not show the half/half. I can take photos of my stone from Gene that categorically DON'T show any half/half. I don't manipulate the photo, it's just that sometimes it really doesn't show it.

Let's be real for a minute. Look at Tiffany's website. Do they declare treatments on their gemstones? No. If you buy a second hand car from a dealer do they point out all the cars faults or do they tell you about the good points? Why would you ask a gemstone dealer to list the flaw of every stone (a flaw YOU may see as a flaw and others don't)?

Here's a really good example http://www.rwwise.com/products/id%7C255 The blurb clearly says this is a beautiful stone. Where does it say about the off centre culet? I can pick tons more examples but this illustrates my point well.

LD, I respectully disagree with you. Although I wouldn't rule out that some of our disagreement has to do with me being unclear or some other misunderstanding, so maybe we won't disagree if I clarify.

I don't think its absolutely not true that "the status quo is that certain optical drawbacks (ie windows) are almost always disclosed by PS vendors. I think we would find it less-than-forthright if a PS recommended cutter did not disclose in a description of the gem that it had a window." I think that statement is true.

I think the first sentence is true. I know vendors like Dana will include in a description of a stone that if it is a bit windowed (these of course are the native cuts that find their way into his inventory). Also of note is that the vendor you mention, RW WIse, will disclose if a stone has a window in his descriptions. CF http://rwwise.com/products/id|2004

Tiffany's most certainly does not disclose treatments. And they are also most certainly NOT among the "PS vendors" to whom I referred. Things like not disclosing treatments would, I hope, keep them off the list. So PS vendors are held to a higher standard. This example is therefore not analogous.

The second sentence also seems true. I do think PS vendors are expected to call attention to certain facts about their stones without provocation. They all list treatments, the good and the bad, as your post reminded me. I think most list windows. I think we would find it less-than forthright if a stone ordered from a PS vendor (at least cutters) that showed a window that couldn't be seen in the picture was not disclosed. Or perhaps more pointedly, let's imagine that in a picture taken in bright daylight, a stone showed a beautiful color. Then in all other lighting, it went completely black. I think we would expect such a poor optical property would be pointed out by a PS vendor. We would be justifiably angry that this fact was not relayed prior to shipping. While I agree vendors want to put their stones in the best light, I think part of what gets them recommended status is a willingness to volunteer certain optical deficincies. (ie "While this stone does show some brown undertones, it does not detract too much..." etc). Since shadowing can be hard to see in a vendor picture (as it was in your garnet), perhaps this is all the more reason to want it disclosed, say, moreso than a large window which is usually easily spotted. I for one would find it helpful, and many on this board have to return stones because they dislike shadowing. LD, you and I agree it is obvious that not all drawbacks can or should make it to a description, but it is equally obvious to me that some potential drawbacks should be mentioned. And many vendors do this. And there is at least a case to be made that persistent shadowing is one such drawback.

We all prize gemstones for different reasons. LD for their uniquenness. Some love the cutting. I prize them for their color, which is why I dislike the shadowing that obscures it.

But my point in this thread was not at all to advocate disclosure of shadowing. I'm not convinced it should or shouldn't be. I was more concerned that people who don't like shadowing can learn a bit more about how to avoid it, which cuts are good at avoiding it, and which ones often exhibit it.

 

[minousbijoux]

I think you can't paint as broad a brush as you are with the preferred vendors - I've had some disclose windows and some not; I've had some disclose extinction, some not. They're human, sometimes they forget. Fundamentally, every vendor is different and blanket statements are hard to make. I too don't agree that they all disclose this but not that.

At this point, have your original questions been answered? I'm sorry there is not a more clear cut answer.

 

[corundum_conundrum]

I agree disclosure is not uniform on any issue. I agree that its incorrect to say that all PS vendors will disclose all optical deficincies, or even any particular deficiency, all the time. So if this is what it I came off as saying, I admit I am wrong.

But I do think its fair to say that many will often disclose things like windows in a description, and almost all of them will disclose treatments even if it is an undesirable treatment. So the status quo is that some negative aspects will be relayed in a description. Curiously, however, I've never seen a description mention shadowing as a draback. Someone can correct me if I am wrong. So its interesting that a small window will often be disclosed, while shadowing is rarely disclosed, although sometimes maybe its obvious enough from the picture (see above pics). I'm not at all crying foul, I'm just calling attention to the fact that shadowing seems to be viewed as not disclosure-worthy, and yet I've seen stones returned for shadowing about as often as stones with small windows. So its not obvious why there is such a gap between disclosure of the two phenomena. But other PSers really take issue with this, and that's fine and they may be right, and this is tangential to my concern.

Thanks for hanging with me Minous. To recap: it seems as though concave faceting, supernova, or barion cuts might be somewhat negatively correlated with shadowing. I would welcome any more thoughts on these issues, but we have had some opinions.

How about keel-cutlets and small tables? Will stones with these features show shadowing less often? A PS cutter also casually mentioned in a thread long ago that certain elongated modified radiant emerald cuts will ALWAYS show shadowing. Can anyone confirm this? The likelihood of shawdowing on various cuts should help in making determinations about which stones to buy (ie avoid radiant emeralds if shadowing bothers you), or what cuts they should request if a stone is custom-cut. I would welcome cutters thoughts about these correlations as well (if they haven't been scared off by all my diclosure talk! I promise I won't ask you about that, just about cuts that do and don't show shadowing!)

 

[LD]

All cuts can show shadowing (or extinction).

 

[corundum_conundrum]

All cuts can show shadowing (or extinction).

Yes, but some seem to more reliably avoid it, while others are prone to it. And a cutter claimed that one cut always shows it! This is what I am trying to map-out.

 

[corundum_conundrum]

I forgot to mention that we also gathered that the effect is less distracting in lighter color stones. I've also read elsewhere that micro-inclusion can cut back on the effect. So just like with regular extinction, the darkness and clarity of the stone will participate in the effect. So maybe buyers should be at their most circumspect when buying loup-clean, darker gems in ovals and rectangles if they don't like the half/half.

 

[corundum_conundrum]

Okay, this thread was sort of a bust. I'm letting go of it. Thanks for your comments, Chrono, Minou and LD. Minou, your thoughts on lighter colored stones was helpful new information for me.

My hope was to discuss some cutting strategies and buying strategies for those who wanted to avoid this effect (when it interferes with the color of one side of the stone). Certainly not everyone thinks this is a big issue, but some do. I wanted to avoid just arguing about whether the effect was so bad, but I devolved into doing just that! I guess this issue is just very contentious. The only other issue that seems to garner such strong feelings is recutting! In case anyone finds this thread through google or something, here's an old thread with some cutters weighing-in that I alluded to. A cutter mentions the solution of a small table in another thread, but its just in passing. You'll have to search for it. So maybe you, o future people, can take-up this issue where I left-off. I didn't get any farther than the things said in this thread:

https://www.pricescope.com/community/threads/oval-cuts-half-n-half-extinction-effect.116619/

 

[OneKuhlChic]

In all seriousness, I ask the vendor in advance. There are very few occasions when the vendor has told me it didn't have it when in actuality it did. It is less frequent with barion cuts and supernovas, but I would still ask the question of the vendor regardless. I find that the effect is less bothersome to me on lighter colored stones as well - if its there, then the stone will read as having color, instead of more pronounced extinction of darker tones. That is while it doesn't eliminate the phenomenon, I can enjoy the color if I choose to keep it.

I think it is isolated to elongated cuts, as I don't remember ever seeing it on rounds, asschers and square cushions, princess, trillions, etc.

I just bought a cushion cut umbalite garnet that shows about 25% extinction. I did some research and it all points to quality of the cut.

 

[Daisys and Diamonds]

Great
Something else to worry about

 

[Frost]

Since this old thread got necromanced, just FYI: it's not really about cut quality so much as proportions. Tone, hue and even variety all have an effect too.

Any elongated cut will be susceptible to it, and even in cuts that aren't long-ish you can still induce it by looking at the stone while it's unevenly lit: if you for example look at a medium or darker-toned round or a square cushion while right next to a window on your left, the right side of the stone will be lit while the left will be dark. If the light source is on your right, the left side will be lit.

That's literally expected behavior and something that's innate to colored gems in general. It's such a non-issue in the trade that the prescribed calibrated size ratios for rectangular cushions and ovals actually make this more likely to occur since those tend to be more elongated than free-size cuts.

As R.W. Wise once pointed out here, colored gems are traditionally judged with the sun/light source behind your back in diffused lighting. That's where you get the "default" look/grade for color, clarity and cut. But gems change with light just like everything else, and it isn't reasonable to expect them to look the same all the time regardless of how they are lit.

As others have pointed out in this thread, people wishing to avoid this should avoid elongated cuts, especially in medium or darker tones (which unfortunately also tend to produce the most "ideal" colors otherwise). Sapphires are a lot more prone to it than tsavorites, Mahenge spinels, or other gems that tend to light up more easily.