Blue sapphires with no half/half extinction?

[lominoblue]

I do not know the type of cut nor the name of the lapidary. I viewed these two about 2 years ago and kept one, sent one home. My intent was to purchase the blue oval and the rectangular was an extra the vendor sent along for my viewing pleasure. We are good friends and he trusts me with his stones. He has since retired from the business. Unfortunately, since I no longer have the rectangular spinel in my possession, I cannot take more pictures of it.

I am concerned that not only is your definition different but you are not reading the pictures accurately. You are sometimes mistaking body colour as the dark part and sometimes mistaking the brilliant part as the body colour. A bow tie isn't necessarily symmetrical nor placed squarely in the center. Not only that, when the lighting condition is just right, the bow-tie lights up and becomes very brilliant.

Ok.. I don't know much about bowties so let's keep it out of this thread. Not to confuse everyone.

As for me having a different "eye" for half/half is very true. So with regard to body color.... it can look ligher or darker depending on how the light hits it right? Or does it stay constant in all orientations such that there is one side with darker body color and the other side with ligher body color? Again, I guess the definition for you guys is that half/half is half black and half light. It seems to me that this definition is confusing because dark body color and black are in the same spectrum... and subjective.

 

[chrono]

It is the one circled in red. It is rotated the other way now and you don't see the effect anymore.

A gemstone is never static - there will be always dark areas and light areas. The colour is never going to look exactly the same throughout the stone but again, this is a different look than colour zoning. This slight contrast is brilliance contrast and makes the stone sparkle and look lively. Extinction is defined as an area that is black or devoid of colour and generally it does not move around. Strong lighting can help the colour show through though. One of the goals of cutting (and gem buying) is to get the stone to show as little extinction as possible. A stone can have a dark body colour but still not be black.

 

[lominoblue]

I'm really confused what you think is half and half lomino? Now granted, I didn't get a lot of sleep last night, so that may be contributing.

Any species of stone can have half and half extinction. Spinel, sapphire, garnet, any quartz, whatever.

They are elongated stones. As we've been saying it's a function of cut. But, I don't know exactly how you are defining half and half, so maybe if we can clarify that better, it would help?

Also, we cannot post videos to PS or links to our own videos at this point. Believe me, I'd love to!

My definition has been: in certain light conditions the gem is half darker and half lighter (and it doesn't have to be perfectly half/half... it can be 1/3 and 2/3). Moreover, this half/half can go away with more light or if oriented differently with respect to the light source.

I've seen others post links to videos... not legal?

 

[lominoblue]

To be continued... have to go work!

 

[LD]

Forgive me but I really don't have time to take photos as I have to make dinner in a minute.

The half/half as you call it is now second from the right. If you look carefully you'll see that the half/half is still there - it's actually physically impossible to get rid of it since it's the colouration of the stone! However, these are colour change sapphires and when I took this photo it must have been between day and evening (and the black background doesn't help) so it's more difficult to see the separation of colour.

Your assessment of vertical/horiztonal is also incorrect. If a stone (and please note I'm not saying sapphire here) exhibits extinction that makes half the stone appear different with a delination down the centre of the stone it will show it in many different positions and may also disappear. To prove this, here is a precision cut garnet (one of my favourites) and cut by Gene (Precision Gem) who has responded to you also. This gem does have half/half but it doesn't detract from the gem and in fact enhances it. I can look at it vertically and make it disappear - I can look at it horizontally and make it disappear. I can also make it look very pronounced. It's a function of how the light hits the gem and the slightest movement changes the way it looks.

 

[chrono]

PSers have coined this half and half for precisely this following reason: one half is black and one half is the body colour. This is split right down the middle of the stone, splitting it into two. If one side is 1/3 or 2/3 black, then that is extinction. It is called half because it is exactly 1/2. A stone can still have a dark body colour, yet not be black.

What you see here is brilliance contrast. There is no half/half. The top and bottom parts show the body colour. There are some small dark areas interspersed here and there which is considered contrast. There is a small darker band in the upper half of the spinel in the picture which I'm surprised the camera caught because I do not see this in person. The light source is coming from the right.

 

[LD]

And more photos, different lighting conditions and more angles of the same stone.

 

[chrono]

LD,
Isn't that a concave faceted stone?

 

[LD]

PSers have coined this half and half for precisely this following reason: one half is black and one half is the body colour. This is split right down the middle of the stone, splitting it into two. If one side is 1/3 or 2/3 black, then that is extinction. It is called half because it is exactly 1/2. A stone can still have a dark body colour, yet not be black.

What you see here is brilliance contrast. There is no half/half. The top and bottom parts show the body colour. There are some small dark areas interspersed here and there which is considered contrast. There is a small darker band in the upper half of the spinel in the picture which I'm surprised the camera caught because I do not see this in person. The light source is coming from the right.

And I think this is one of the issues Chrono. (This post is not aimed at you Chrono by the way, it's just a general rant)!

As there's no such thing as half/half and it's basically a descriptor for seeing a gem with a split in the middle with light/shading going on - some people say it has to black out in one half, others think that a variation in colour/tone qualifies as half/half!

At the end of the day THERE'S NO SUCH THING and this is why I get so upset at people using it willy nilly because it's all extinction with varying degrees. In some gems half is so blacked out that the stone is incredibly unattractive, in others it can be beautiful. People searching for gemstones with NO extinction will be searching a very long time unless they can adjust the sun and all light sources so that there's a planet with no light/shade!

Phew, I feel better now!

 

[LD]

LD,
Isn't that a concave faceted stone?

It's not a traditional concave Chrono. Hopefully Gene can chime in but I think this is one of his own cuts. Which pretty much dispels the theory that concave cut gems won't show half/half!

 

[chrono]

No, no, no, I quite agree with you. At the end of the day, it is still extinction.

Do you think you are seeing two different colours (not extinction!) due to the type of light hitting the stone? Some garnets are notorious shifters and perhaps the cut brought this feature out more easily?

 

[LD]

No, no, no, I quite agree with you. At the end of the day, it is still extinction.

Do you think you are seeing two different colours (not extinction!) due to the type of light hitting the stone? Some garnets are notorious shifters and perhaps the cut brought this feature out more easily?

It's not a "normal" colour shifter Chrono because in some lighting conditions the two ends are the same but rotate the gem ever so slightly and you see half of the gem change. With a normal colour shifter this wouldn't happen - the whole thing would change. There are areas of extinction but you're right it reacts differently depending on how the light hits the stone and I believe Gene's wonderful cutting is responsible for this.

I've actually got an interesting colour change garnet that is donkey brown in daylight and the extinction is incredibly prominent BUT at night this ugly duckling turns into a princess and looks like a glass of fine shiraz wine with very little extinction! Again, it's all about the light with this gemstone!

 

[PrecisionGem]

I think the term "half and half" was invented here on Pricescope. I have never heard it before in the trade. Normally the effect you are referring to is called "shadowing". This is can be seen in stones where the pavilion does not have full symmetry. In the picture of the long oval I posted, all the main facets on the pavilion were cut at 42 degrees. Additional facets were then added so that the stone would fit to the 2:1 profile, but the facets that are doing the work are all symmetrical. In the stone the LD posted of mine, which by the way is concave cut, the pavilion facets are not all the same angle.

If you look at the picture posted above of the SuperNova design, all the facets with the number 1 on them are at the same angle. These are doing most of the work in the pavilion of the stone, and produce more symmetry to the stone. There are designs that work better than the SuperNova, and I would think because there is even more symmetry to them. I don't cut the SuperNova much as I prefer more smaller facets in the pavilion for most stones. In a darker stone, then these fewer larger facets can work better.

Some poorly cut rounds and other shapes can also produce this effect, but not as common as the ovals. Any stone if you light it from certain angles can produce areas of brightness and extinction.

 

[LD]

I think the term "half and half" was invented here on Pricescope. I have never heard it before in the trade. Normally the effect you are referring to is called "shadowing". This is can be seen in stones where the pavilion does not have full symmetry. In the picture of the long oval I posted, all the main facets on the pavilion were cut at 42 degrees. Additional facets were then added so that the stone would fit to the 2:1 profile, but the facets that are doing the work are all symmetrical. In the stone the LD posted of mine, which by the way is concave cut, the pavilion facets are not all the same angle.

If you look at the picture posted above of the SuperNova design, all the facets with the number 1 on them are at the same angle. These are doing most of the work in the pavilion of the stone, and produce more symmetry to the stone. There are designs that work better than the SuperNova, and I would think because there is even more symmetry to them. I don't cut the SuperNova much as I prefer more smaller facets in the pavilion for most stones. In a darker stone, then these fewer larger facets can work better.

Some poorly cut rounds and other shapes can also produce this effect, but not as common as the ovals. Any stone if you light it from certain angles can produce areas of brightness and extinction.

Thank you Gene because I wasn't sure! Are the crown facets different also to a traditional concave (I need to say that I don't own any other concaves so I can't compare because I actually don't like them!? LOL By the way, it's mine now, not yours and you're not having it back

 

[chrono]

LD,
Please don't get mad but the crown looks checkerboard-like (multitude of squares).

Gene,
Thank you for the explanation. It makes sense to me and I'll have to keep this as reference.

 

[LD]

LD,
Please don't get mad but the crown looks checkerboard-like (multitude of squares).

Gene,
Thank you for the explanation. It makes sense to me and I'll have to keep this as reference.

LOL not mad Chrono - stressed to the hilt and trying to cook! To be honest, I haven't looked at the photos carefully and have been posting at the speed of light. You're right however it does look checkerboard!

 

[FrekeChild]

I'm really confused what you think is half and half lomino? Now granted, I didn't get a lot of sleep last night, so that may be contributing.

Any species of stone can have half and half extinction. Spinel, sapphire, garnet, any quartz, whatever.

They are elongated stones. As we've been saying it's a function of cut. But, I don't know exactly how you are defining half and half, so maybe if we can clarify that better, it would help?

Also, we cannot post videos to PS or links to our own videos at this point. Believe me, I'd love to!

My definition has been: in certain light conditions the gem is half darker and half lighter (and it doesn't have to be perfectly half/half... it can be 1/3 and 2/3). Moreover, this half/half can go away with more light or if oriented differently with respect to the light source.

I've seen others post links to videos... not legal?

Not our own videos. I have a lot of those of gems, but I can't post them!

 

[PrecisionGem]

LD on YOUR stone, the crown is square checkers, and the pavilion concave.

Being in the UK, you should know that "half and half" means a pint of beer with half Guinness and half Smithwicks Ale, Guinness on top! Here in the US we commonly use Bass Ale on the bottom. Some bars call it Black and Tan, but I don't think that is correct.

 

[LD]

LD on YOUR stone, the crown is square checkers, and the pavilion concave.

Being in the UK, you should know that "half and half" means a pint of beer with half Guinness and half Smithwicks Ale, Guinness on top! Here in the US we commonly use Bass Ale on the bottom. Some bars call it Black and Tan, but I don't think that is correct.

Now that's a half/half my hubby would approve of! You're right, the Irish would chuck you out of a bar if you ordered a black and tan! In many Irish bars it would be the equivalent of ordering a “General Sherman” in the Deep South.

As a good Londoner and Cockney, I much prefer a St Clements (half orange juice/half lemonade)! Although generally speaking anything with alcohol hits the spot better!

Thanks for clarifying Gene. It's odd because I "normally" don't like concave or checkerboard cuts so it just goes to show that colour trumps everything!

 

[corundum_conundrum]

One of the things that I will take from this thread (thanks Gene!) is that there is a term in the trade for this phenomena: "shadowing." I think this is something to ask about when inquiring about a stone you might want to purchase. I'm removing that *other phrase* from my lexicon.

Also, other cutters have said in the past that the keel culet is a bad idea if you want to avoid shadowing.

I've learned through this board that shadowing can be exhibited on a spectrum--sometimes it inhibits brilliance of one side of the stone completely (resulting in a blackout!), and other times it just causes a two-tone effect. This spectrum of "shadowing" means that not all shadowing is so bad. For example, in dark material like a royal blue sapphire, it might cause one side of the stone to "black-out," which most will find objectionable. In a pink danburite, it might just cause a two-tone pink effect, which is not nearly as objectionable as the black-out, and can be downright interesting.

 

[corundum_conundrum]

I love checkerboard crowns! Especially when they have a little twist like I think they do is LDs lovely stone, or done corner to corner etc instead of side-to-side.

 

[LD]

One of the things that I will take from this thread (thanks Gene!) is that there is a term in the trade for this phenomena: "shadowing." I think this is something to ask about when inquiring about a stone you might want to purchase. I'm removing that *other phrase* from my lexicon.

Also, other cutters have said in the past that the keel culet is a bad idea if you want to avoid shadowing.

I've learned through this board that shadowing can be exhibited on a spectrum--sometimes it inhibits brilliance of one side of the stone completely (resulting in a blackout!), and other times it just causes a two-tone effect. This spectrum of "shadowing" means that not all shadowing is not so bad. For example, in dark material like a royal blue sapphire, it might cause one side of the stone to "black-out," which most will find objectionable. In a pink danburite, it might just cause a two-tone pink effect, which is not nearly as objectionable as the black-out, and can be downright interesting.

Bingo!

What I will say is that even if you ask about shadowing you could still end with a gem you don't want!

 

[lominoblue]

PSers have coined this half and half for precisely this following reason: one half is black and one half is the body colour. This is split right down the middle of the stone, splitting it into two. If one side is 1/3 or 2/3 black, then that is extinction. It is called half because it is exactly 1/2. A stone can still have a dark body colour, yet not be black.

What you see here is brilliance contrast. There is no half/half. The top and bottom parts show the body colour. There are some small dark areas interspersed here and there which is considered contrast. There is a small darker band in the upper half of the spinel in the picture which I'm surprised the camera caught because I do not see this in person. The light source is coming from the right.

And I think this is one of the issues Chrono. (This post is not aimed at you Chrono by the way, it's just a general rant)!

As there's no such thing as half/half and it's basically a descriptor for seeing a gem with a split in the middle with light/shading going on - some people say it has to black out in one half, others think that a variation in colour/tone qualifies as half/half!

At the end of the day THERE'S NO SUCH THING and this is why I get so upset at people using it willy nilly because it's all extinction with varying degrees. In some gems half is so blacked out that the stone is incredibly unattractive, in others it can be beautiful. People searching for gemstones with NO extinction will be searching a very long time unless they can adjust the sun and all light sources so that there's a planet with no light/shade!

Phew, I feel better now!

Well I think this sums it up. This is the problem that I have with it. Many times people say there is half/half when really it is just two tones of color and not half black and half color.

And it is simply a spectrum. It can be black and white or it can be medium gray and dark gray half/half.

I've read about shadowing from someone who is in the trade and basically he said all exhibit it because it is coming from a specific light source.

Ultimately I can see how some cuts can minimize shadowing.

 

[lominoblue]

And more photos, different lighting conditions and more angles of the same stone.

See... I would have said before that even this beautiful pink precision cut gem has half/half and I think others have used the term as such.

Which brings me back to the question... is there an oval without the ligther body and darker body contrast or shadowing? Because I can see how some don't half/half if the definition is black on one half and body color on the other half.

 

[lominoblue]

One of the things that I will take from this thread (thanks Gene!) is that there is a term in the trade for this phenomena: "shadowing." I think this is something to ask about when inquiring about a stone you might want to purchase. I'm removing that *other phrase* from my lexicon.

Also, other cutters have said in the past that the keel culet is a bad idea if you want to avoid shadowing.

I've learned through this board that shadowing can be exhibited on a spectrum--sometimes it inhibits brilliance of one side of the stone completely (resulting in a blackout!), and other times it just causes a two-tone effect. This spectrum of "shadowing" means that not all shadowing is so bad. For example, in dark material like a royal blue sapphire, it might cause one side of the stone to "black-out," which most will find objectionable. In a pink danburite, it might just cause a two-tone pink effect, which is not nearly as objectionable as the black-out, and can be downright interesting.

gene> is the keel bad because it has more shadowing?

 

[Lula]

No, no, no, I quite agree with you. At the end of the day, it is still extinction.

Do you think you are seeing two different colours (not extinction!) due to the type of light hitting the stone? Some garnets are notorious shifters and perhaps the cut brought this feature out more easily?

It's not a "normal" colour shifter Chrono because in some lighting conditions the two ends are the same but rotate the gem ever so slightly and you see half of the gem change. With a normal colour shifter this wouldn't happen - the whole thing would change. There are areas of extinction but you're right it reacts differently depending on how the light hits the stone and I believe Gene's wonderful cutting is responsible for this.

I've actually got an interesting colour change garnet that is donkey brown in daylight and the extinction is incredibly prominent BUT at night this ugly duckling turns into a princess and looks like a glass of fine shiraz wine with very little extinction! Again, it's all about the light with this gemstone!

I laughed out loud, LD, and almost spilled my glass of wine on my keyboard What an interesting stone.

 

[lominoblue]

One of the things that I will take from this thread (thanks Gene!) is that there is a term in the trade for this phenomena: "shadowing." I think this is something to ask about when inquiring about a stone you might want to purchase. I'm removing that *other phrase* from my lexicon.

Also, other cutters have said in the past that the keel culet is a bad idea if you want to avoid shadowing.

I've learned through this board that shadowing can be exhibited on a spectrum--sometimes it inhibits brilliance of one side of the stone completely (resulting in a blackout!), and other times it just causes a two-tone effect. This spectrum of "shadowing" means that not all shadowing is so bad. For example, in dark material like a royal blue sapphire, it might cause one side of the stone to "black-out," which most will find objectionable. In a pink danburite, it might just cause a two-tone pink effect, which is not nearly as objectionable as the black-out, and can be downright interesting.

This was very well said. The tone of the body color would have implications for the amount of shadowing. Which is probably why a lighter color stone would appear to have less black out (strick definition of half/half).

 

[lominoblue]

I found this useful bit. Too bad supernovas have to be made deeper.

I see how symmetry would help eliminate half/half contrast or shadowing or whatever you want to call it. Symmetry is hard to obtain in an oval, but easy to obtain in a round.

Gene > What is the drawback of having some of the facets do most of the "work" like the 1's in a supernova. Do you get less scintillation? Since the cut really matters, is the traditional step cut inherently always going to have a more severe shadowing? In oval diamonds, how come one doesn't see shadowing?

 

[FrekeChild]

One of the things that I will take from this thread (thanks Gene!) is that there is a term in the trade for this phenomena: "shadowing." I think this is something to ask about when inquiring about a stone you might want to purchase. I'm removing that *other phrase* from my lexicon.

Also, other cutters have said in the past that the keel culet is a bad idea if you want to avoid shadowing.

I've learned through this board that shadowing can be exhibited on a spectrum--sometimes it inhibits brilliance of one side of the stone completely (resulting in a blackout!), and other times it just causes a two-tone effect. This spectrum of "shadowing" means that not all shadowing is so bad. For example, in dark material like a royal blue sapphire, it might cause one side of the stone to "black-out," which most will find objectionable. In a pink danburite, it might just cause a two-tone pink effect, which is not nearly as objectionable as the black-out, and can be downright interesting.

This was very well said. The tone of the body color would have implications for the amount of shadowing. Which is probably why a lighter color stone would appear to have less black out (strick definition of half/half).

Color and species have no bearing on shadowing/half and half extinction. I had a spinel once upon a time that was a nice lighter gray-blue, but one side lit up and the other was black.

 

[SapphireSun]

Sorry just had to chime in. This is a fascinating thread because I think I know where the OP is going with this. When I posted my blue sapphire I knew there was something about it, but not necessarily bad. It was then brought to my attention that it had this "half and half" extinction. Well, when I brought this up with NSC they had a fit because they were adamant my stone did not have this and did not like the term. I then contacted a gemologist who informed me its not the stone, but the cut which shows half of the stone a lighter color. So, yes you may find blue sapphires without this distinction if they were cut differently. Here's why I love my stone: it does not go black on one half but does show contrast, one side a lighter shade of blue than the other, and it is not always present. Only when indoors under low lighting. Under bright lights or outside it is fully saturated and sparkles. This contrast to me shows more life because of the different hues of blues it throws out. It's not just one shade of blue. I just updated my post because I had noticed many newbies in search of that perfect sapphire and thinking this distinction is a flaw. At first I thought so too when it was brought to my attention because of the critical way it was presented, but its not. Some may not prefer it, but everyone has their preferences, it just doesn't mean one way is better than the other. Find a stone you love that is not heavily windowed or black with extinctions and you will be happy. If anything there should be a new thread for those who love their oval blue sapphires with this distinction! I may be the only one on PS!

P.S. you can find my thread right below this one to see photos of my ring.