Spinels, Polish, Luster and Sparks

[minousbijoux]

I was selling some spinels recently and realized that two precision cut stones I had - and have now sold - threw off the most amazing sparks of color. One was a lavender/periwinkle/pink stone and it throws off these sparks of peach, pink, light blue, and purple in the right light. I also had this Platinum blue color shift spinel that threw off sparks of purple, blue, teal and peach in the right lighting. This is what makes a great spinel IMO. So my question: what causes the sparks? Is it that they only come from one locale? For example, I know that Burmese spinels seem to consistently throw off these sparks, or is it something else? Is it the nature of the precision cutting and the high polish and luster? I am very interested as some of the spinels I have left have it, and others don't and I would love to know when to expect it. Like could you go buy any large, deep, good clarity spinel on ebay and have it recut by a precision cutter and would it throw off sparks?

I'd love any advice or thoughts on this, as those sparks are just so amazing.

TIA

 

[Arkteia]

Out of the ones I have, only the round, very clean, spinels have sparks. Not necessarily the best quality/color stones, but very bright. It seems that dark spinels do not perform this way. I have a couple of hot pink, very clean spinels, portugueze cut, and well-polished, too, and they do not have the "sparks" although they are very bright. So I am not sure a recut would do it for each spinel.

 

[innerkitten]

I have a round lavender one that does that. But I also have a badly cut peachy one with a big window that has sparks around the edges.

 

[sapphirecats]

wow, don't know what causes the sparks, but I sure am sorry I missed the sale!! I would love a lavender color one... on the lookout!

 

[chrono]

It is a function of several things, namely the RI and luster of the spinel, tone, saturation and also faceting. I noticed this a few years ago and did my own unscientific study / observation. I used my own spinels as samples, including others I have seen but do not own. Some are precision cut and the remaining are very good non-precision cut stones.

All spinels have the same high RI and very good luster which is great. But why do certain hues tend to show multi-coloured fireworks more than others?

Blue spinels - if the tone is dark, it will show blue flash only. If the tone is light to medium, you will see fireworks. In this case, I believe the cause is due to the dark tone dampening the breakdown of light into its spectral colours. It does not seem dependant on origin (Sri Lankan, Tanzanian and Vietnamese blue spinels).

Red spinels - have not observed multi-coloured fireworks, only red flash. Again, I think this is a function of tone. It does not appear to be dependent on location (Tanzanian, Burmese and Vietnamese red spinels). Pink is a light toned red. I noticed that pink spinels (due to the lighter tone) has a tendency to throw off more sparks of different colours. However, hot pink spinels do not seem to show fireworks. Yes, it is still brilliant and very sparkly but only has pink flash. I wonder if it is because it is very saturated? My baby pink spinel has lots of fireworks probably because it is both light in tone and not a hot pink (less saturated). My hot pink Mahenges have only pink flash but lots of pink flash.

Lavender/periwinkle/light violet spinels - these are almost always a medium light tone and consistently throws off fireworks. None are super saturated or "hot" although saturation is still strong. Mine come from Vietnam and Tanzania so origin isn't a factor. One is precision cut and the other isn't, but both are disco balls of light.

Result:
It is not dependent on origin.
It is not dependent on cut, unless it is terribly cut then obviously light is going to leak right through. A poor polish is going to show some effect as well but not as much as the other reasons.
It is dependent on tone (must be medium or lighter)
It is dependent on saturation (must be strong or lighter)

 

[mastercutgems]

Hello All

Coming from the cutter aspect... on the location and what optics are presenting this effect. When you get down to the nitty gritty on the elemental make-up of the gem... location is a factor on optics...

Why else would you prefer a Burma ruby over one from say Madagascar??? They both will be defined per the lab as a ruby BUT the elements that make up the gem mineral are slightly different and will alter the glow effect, etc...

I do find that Burma spinels will have more dispersion than the Sri Lanka or Tanzanian material. Now granted they all 3 will have some slight tone difference but they are all in the same hue/color , size, exact same angles for the cuts, etc... As when doing a lab experiment; you have to keep apples with apples. Now we may be comparing Red delicious with Stayman Winesap's; but they are both apples... both red but with different chemical makeups with different tastes

The Burma location material threw off at least 30 to 40 % more reflective, dispersion or rainbow effect type light than the other two; and the Tanzanian material about 10% more than the Sri Lanka material...

There are also things that have effect on this and I am sure another good cutter like Gene, etc. can concur that crown angles, the amount of facets the alignment of facets; smaller table more scintillation, etc. can all be determining factors in this along with the quality of the polish as that really has much effect.

As most know I do a lot of re-cutting and the non-precision cuts usually have the shallow crown facet angles like in the high teens and their polish is less than desirable; but I can re-cut the pavilion with a high polish and get much more light return; but the amount of light reflectivity on the crown is still minimal; but if I go in and restore the crown even in the low 20 degree angles which is still about 10 degrees lower than desired I will still pick up a considerable amount of scintillation and reflectivity as much of it is the polish as we most of the time use 50,000 diamond mesh and many use 12 to 20,000 mesh in other countries as it saves time...

Sorry for the long windedness of the post but it take time to explain things in a manner which has facts behind it...

There is method to the madness...

Cutters chime in As I am always willing to hear your opinions on the cutting and polishing of gems.

I know I just got finished with one for my personal collection; a Hotazel South African Rhodochrosite that is a little over 2.77 carats and the color is blinding pink-orange... But back to the point of the discussion the Peruvian material of which I have cut 3 does not even compare to this location and they both are the same cut...But the difference in the two gems with the same cut is dramatic as the South African gem throws off at least 30% more reflective light than the Peruvian material... So location of a said mineral can and will have an effect on things like reflectivity of the light as they are not totally identical in the elemental make-up of the gem mineral and that does effect some things.
It goes on and on as some tourmalines do the same thing as there was a location of Afghanistan Tourmaline from Badakshan that has a much higher dispersion or reflectivity than any other tourmaline I have ever cut; unreal... So the list goes on and on with different minerals; location does have an effect on the optics of a gem when cut...

Just my opinion...

Most Respectfully;

Dana Reynolds
ASG Certified Supreme Master Gem Cutter # 96cge42

 

[minousbijoux]

Wow, thanks for the responses. Dana and Chrono, really great to hear both your experiences - one from the collector's POV and one from the master cutter. I'd love to hear from TL, or Freke or any of the cutters like Gene as to what their experience has been. Come to think of it, I'm not sure I've ever bought a spinel from Gene. So far, my favorites are from Barry and Dana.

 

[PrecisionGem]

By sparks, I guess you mean dispersion?

Spinel doesn't have real high dispersion, it's about midrange for stones. In darker stones it's harder to see dispersion, so the more midrange tone wise stones will show dispersion better. As Dana mentioned, dispersion can be enhanced by a higher crown and facet placement. So unfortunately it comes down to cutting again. Same material, two different cuts and will will "throw sparks" and the other won't.

The higher the refractive index, and the higher the dispersion, the sloppier you can get with the cutting and still have a flashy stone. It always seems odd to me that people say cutting is important in diamonds, but not colored stones. You can really screw up the angles on a diamond and still get a stone with sparkle and dispersion. To get a lively quartz or tourmaline the angles and facet placement are much more critical.

 

[NKOTB]

Well, I have a spinel cut by Dana that is sometimes silver, sometimes quite dark grey, sometimes with some bluish, sometimes with some purplish. But this is the stone that made me realize what dispersion meant. Only sometimes medium in tone (and sometimes darker). Given the amount of grey, I guess it would be lower on the saturation scale, from Tunduru. Fancy round brilliant. Crazy sparks! FWIW...

 

[minousbijoux]

But if it doesn't have terribly high dispersion, why are the sparks - or dispersion - on some of these spinels so much more noticeable than any other stone? I can't think of another stone I've seen it on, except diamond and maybe demantoid. I think you're right cutting has a lot to do with it, because the less well cut spinels I've picked up on ebay haven't had it. I do think I would agree that its more prominent in the lighter stones, except that like NKOTB, I have a fairly dark spinel from Dana that has gorgeous flashes of color other than the color of the body of the stone. So it sounds like its a combination of saturation and tone, cutting and maybe, location. I would love to hear from others, such as our spinel collectors!

 

[FrekeChild]

Lol. I don't really have a lot to say on the matter (brain dead from long term sleep deprivation methinks!), but I have noticed more dispersion based on a couple of factors:

-precision cut
-lightness/darkness

If a stone is precision cut, and a light color, I think there is a much higher chance of seeing some serious sparks. I have several darker stones (counting hot pink here) and they just show me flashes of color, they don't show dispersion. Now, often those are not precision cut, perhaps that factors in? But I have had many stones from Barry Bridgestock, spinels by the dozens, and every single one of his have shown dispersion, but the darker ones show less. (All of my precision cut spinels show dispersion to some degree!)

I also have a little fireball of dispersion in my almost colorless garnet asscher... (the colorless stones are the best!)

To sum it up: Beats the heck out of me, but I'll keep buying spinels anyway!

 

[chrono]

As they say, pictures say it all without words. I'm not a good photograper so please bear with me. These are what I consider the "no sparks" camp but to be accurate, there are sparks but are inconsequential compared to the "fireworks" spinels.

Picture 1
Precision faceted blue spinel by Barry Bridgestock and a non-precision cut blue spinel purchased somewhere else. The BB spinel is of African origin (Tunduru) and I don't recall where the other one is from. Mostly blue flash with the occasional dispersion. If I do see dispersion, they are very small, being limited to the edge of a facet or something similar.

Picture 2
My Mahenge spinels show mostly flashes of body colour, with the occasional very small rainbow spark. This includes the pear shown and also 2 pairs of hot pink trillions. Just big bold colour almost all the time.

Picture 3
I own several Burmese red spinels and chose these because they are easier to photograph as they are already set. Lots of red flash and I don't recall seeing any sparks. If I did see any, they did not make an impression because the red took precedence and/or they were very small and infrequent.

 

[chrono]

These are the very dispersive spinels. Note that the tone is lighter.

Pictures 1 and 2 are of the same spinel.
Precision faceted violet blue spinel from Luc Yen. Crazy dispersion which I cannot capture accurately. It is literally a fireball of colour almost ALL the time.

Picture 3
Precision faceted colour changer from Luc Yen. It is a pink to violet spinel. Again, this one is just throwing off crazy sparks all the time.

I have not taken any pictures of my new non-precision cut spinel which is another fireball of dispersion. It is violet in colour and a medium in tone. This one also shows unbelieveable sparks constantly. I think it is of African origin.

 

[innerkitten]

Wow! I like all those photos but that last spinel photo is really cool! Is that a cat or some type of home decor in the photo with the ring?

 

[chrono]

Wow! I like all those photos but that last spinel photo is really cool! Is that a cat or some type of home decor in the photo with the ring?

Are you referring to my picture with the pear ring? If so, yes, that's my kitty in the background. She likes to follow me all over the house like a dog.

 

[minousbijoux]

IK: you don't miss a thing!

Freke I hope you can stay awake long enough for me to thank you for dropping by . I think of you as the person who has more spinel experience than anyone, so thanks for your input and pics.

Chrono: stunning photography and stones. On the one hand, I love your pure saturated stones. Those Burmese reds are stunning. But the stones from Luc Yen are amazing in their dispersion. Now I know what to work towards.

At the end of the day, I think you've demonstrated that its not as much location, as it is tone. I also wonder if the high grade luster from precision cutters allows more of the refracted light to pass back through the stone, thereby creating more dispersion? But I'm probably splitting hairs at this point. What I know for sure: love the dispersion and we have seen some very, gorgeous stones!

 

[NKOTB]

Chrono, that violet blue Luc Yen spinel is one of the most beautiful stones I have EVER seen a picture of!! I say this in the ridiculous way that PSers say it when they know the other person would never part with such a beauty, but DIBS!!!

 

[chrono]

Chrono: stunning photography and stones. On the one hand, I love your pure saturated stones. Those Burmese reds are stunning. But the stones from Luc Yen are amazing in their dispersion. Now I know what to work towards.

At the end of the day, I think you've demonstrated that its not as much location, as it is tone. I also wonder if the high grade luster from precision cutters allows more of the refracted light to pass back through the stone, thereby creating more dispersion? But I'm probably splitting hairs at this point. What I know for sure: love the dispersion and we have seen some very, gorgeous stones!

InnerKitten,
I'd better be more aware of the background before I post pictures on PS or else you will be able to figure out everything about my house.

Minous,
Thank you for the compliment. I sure wish I can take better pictures like Kenny but alas, I'd rather spend my money on more gems instead of fancier high quality camera equipment. There is no question that if all else is equal, precision cutting will bring out better sparks than not so nice non-precision cut stones. A high crown with the correct pavilion angles, coupled with higher grit polish will maximize the beauty of the gem, regardless of its colour, saturation and etc.

NKOTB
Good try! I'm sending it off to be set tomorrow so I'll be creating a thread for CAD reviews later in the month. PSers are a very helpful group of people who've contributed so much in sharing their opinions on just about everything. I would not feel comfortable giving any go-ahead for a jewellery design without additional pairs of eyes to catch anything I might have missed.

 

[innerkitten]

IK: you don't miss a thing!

Freke I hope you can stay awake long enough for me to thank you for dropping by . I think of you as the person who has more spinel experience than anyone, so thanks for your input and pics.

Chrono: stunning photography and stones. On the one hand, I love your pure saturated stones. Those Burmese reds are stunning. But the stones from Luc Yen are amazing in their dispersion. Now I know what to work towards.

At the end of the day, I think you've demonstrated that its not as much location, as it is tone. I also wonder if the high grade luster from precision cutters allows more of the refracted light to pass back through the stone, thereby creating more dispersion? But I'm probably splitting hairs at this point. What I know for sure: love the dispersion and we have seen some very, gorgeous stones!

Well besides the fact that I can spot a pearl necklace ( or any other type of jewelry) from across the street. I also never miss a furry animal.

 

[innerkitten]

That came out weird. Lack of sleep.

 

[Kim Bruun]

Chrono, that Luc Yen spinel is indeed gorgeous, as I have said before - stupendous colour! If you ever have the opportunity to film it, please do! It would be really cool to see the fire moving in it, and a photo can never quite convey how the stone performs.

 

[NKOTB]

NKOTB
Good try! I'm sending it off to be set tomorrow so I'll be creating a thread for CAD reviews later in the month. PSers are a very helpful group of people who've contributed so much in sharing their opinions on just about everything. I would not feel comfortable giving any go-ahead for a jewellery design without additional pairs of eyes to catch anything I might have missed.

Dang!

Well, I second what Kim said. Would love to see a video! And look forward to the CADs, and seeing the finished piece!

 

[ChrisA222]

Chrono, if you ever get tired of looking at those blue spinels...especially the round one...I know of a great new home for it...he he.

 

[chrono]

Am I under the mistaken presumption that we cannot post videos here?

Chris,
I did seriously consider selling the BB blue spinel about two years ago but looking at how difficult it is to get good spinels lately, plus the increase in pricing made me change my mind.

 

[FrekeChild]

MB, you give me entirely too much credit.

 

[minousbijoux]

MB, you give me entirely too much credit.

There's no denying the photographic evidence, my dear!

 

[Lisa Loves Shiny]

Chrono's spinels are TDF. I wish my spinels threw off sparks. They glow, they sparkle, but none spark. Now I WANT one that sparks. Arghhh!!!

 

[1001smiles]

I am a little late to the party, but I thought I'd add some pics.

For me, I think the spinels that are light and well-cut are the sparkliest, and then some have good dispersion and some don't.

These two lavender ones are Tanzanian...



And this one is from Burma, almost colorless. Probably the best dispersion I've seen in spinel (especially in an asscher cut).



Dana has another similar spinel from Birma in a cushion cut, it's still available and I bet it will sparkle
http://mastercutgems.com/index.php?page=viewgem&id=6577