FCD: light performance question

[luigivampa]

How can one measure the light performance of fancy colored diamonds? Do any of the techniques for colorless diamonds (ideal scope) work also for FCDs?

I have looked at enough (still not many) FCDs to appreciate that some have good light performance and some do not. But I don't know if there are tools to assist and quantify what to date has been a qualitative process for me of simply viewing stones. Obviously, logistics make it difficult to view many fancy colored diamonds since they are usually with vendors spread across the globe.

 

[Rhino]

Tools would be the same for judging light performance as it is with any other shape, some being more useful than others. Just a word of note though. FCD's are generally NOT cut with light performance issues in mind the way most communicate it here on the forum (via ASET, IdealScope etc.).

You see ... color in diamond is enhanced and absorbed the more it is cut to emphasize light leakage (not return) and is why you see many diamonds like Radiant's, cushions, cut to fancy colors.

 

[chrono]

I think that the ASET can be used for FCDs but if you want light performance on top of having fine colour, it'll be a long wait to find the right stone that combines the two qualities. As Rhino has explained, FCDs fall into the coloured gemstone category where the primary focus and what sets the price is colour, not light performance.

 

[luigivampa]

Thank you Rhino and Chrono. The reason for the question is that it seems that light performance is what separates diamonds from other gemstones, so if you cannot get good color and good light performance, then maybe another colored gem is just as good a choice. I'm oversimplifying, I'm sure.

 

[chrono]

I am likely to get killed for writing this in RT but here goes. With colourless diamonds, there is no colour to speak of. Without light performance, it is going to look like clear glass and be absolutely boring. Even with ideal light performance, there are times when it is just going to look plainly white, and dare I say, a bit boring. However, with good cutting, it is going to show the spectral dispersion that diamonds are well known for.

Coloured gemstones (FCDs and others) are evaluated completely differently because well....it has colour. It does not need ideal or precision cutting to look beautiful to the eye because the neon colours are what draws the eye to the stone. Of course a yucky cut is a yucky cut no matter what, but even a good to very good cut is enough to catch the eye if the colour is there to begin with.

With other coloured gemstones, depending on the type, you will get flashes of the body colour. With others, you will get flashes of body colour and some neighbouring colour on the colour wheel. What sets FCDs apart from other coloured gemstones is that if it isn't too dark, you CAN still get spectral dispersion. You can get good colour and good light performance, just don't expect ideal light performance. Evaluation of light performance is done by viewing the stone in person, not by any tools because frankly, I think they will all fail if the traditional colourless diamond tools are used.

 

[Rockdiamond]

HI everyone!

What is light performance?
Could it be a preference in how a diamond looks- another way of stating this is it's optical signature.
There's different type of sparkle that comes off of diamonds.
Brilliance, and brightness are not necessarily perceived the same way.
For example, a well cut radiant may be demonstrably less brilliant on ASET or other reflector devices when compared to a super ideal round- yet appear brighter overall in many real life lighting scenarios due to lack of contrast- and a larger number of reflections returning to the eye.

We can agree there's an "optimal light performance range" in round diamonds based on the standardization.
But this is not possible with any fancy shape.
So when applying the term "light performance" to fancy shapes, and fancy colors, we're speaking preference- nothing more. There's no agreed upon standard of what's right.

 

[kenny]

FCD's are generally NOT cut with light performance issues in mind the way most communicate it here on the forum (via ASET, IdealScope etc.).

True.

You see ... color in diamond is enhanced and absorbed the more it is cut to emphasize light leakage (not return) and is why you see many diamonds like Radiant's, cushions, cut to fancy colors.

False.

FCDs are not cut to emphasize light leakage.
They are cut to emphasize color strength, so the get a higher color grade and price.
This is not the result of leakage.
It is the result of positioning the facets to force the light to bounce back and forth more times through the colored body material.
This makes it pick up more light before it is finally forced back out the top, the only view considered when GIA grades FCDs' color.
Radiant and cushion are cuts that can do this, and is why so many FCDs are Radiant and cushion.

That said, yes many FCDs DO have light leakage as a result of saving the weight of the unfortunately-shapped rough and cutting them too shallow.
ALSO, you CAN find FCDs with good light performance, but it will take time.
I have a couple.
Just keep in mind all FCD vendors want to sell every FCD in stock and it's not their fault they are rarely cut to optimize light performance.
IMHO it is just luck that the shape of an occasional rough results in cutting decisions for weight and color to ALSO happen to maximize light performance.
It's the lucky accident that I look for.

Yes you could use an idealscope or ASET to evaluate light performance after you buy it since FCD vendors usually don't offer such pics.

I'm an FCD collector with a dozen that form a rainbow. Click here
Over the years I've bought 20 and returned 8.
I think the only way you are going to find an FCD with good light performance is to buy it and judge it in person, so deal with a reputable vendor with a no questions asked money back policy.

All of my FCDs were bought from Leibish & Co. www.fancydiamonds.net and I cannot recommend this vendor strongly enough.
They have an enormous selection and great service.
Stick with GIA-graded FCDs.
Most of the FCDs that I returned was because I wasn't happy with the light performance, but I have kept a few with poor light performance just because they had superb and rare color, the first priority for most FCD collectors.

Tonight I put them in the Halloween candy bowl for a fun pic.
Then when I brought the bowl outside I forgot to take them out before the first kids arrived.
Glad I noticed them and grabbed them before a kid did.
Two kids passed them up and took candy.

 

[distracts]

Tonight I put them in the Halloween candy bowl for a fun pic.
Then when I brought the bowl outside I forgot to take them out before the first kids arrived.
Glad I noticed them and grabbed them before a kid did.

Man, I would have LOVED trick-or-treating at your house!

 

[kenny]

Tonight I put them in the Halloween candy bowl for a fun pic.
Then when I brought the bowl outside I forgot to take them out before the first kids arrived.
Glad I noticed them and grabbed them before a kid did.

Man, I would have LOVED trick-or-treating at your house!

They might look sweet, but they'd probably chew up your teeth like they were candy corn.

 

[Christina...]

Tonight I put them in the Halloween candy bowl for a fun pic.
Then when I brought the bowl outside I forgot to take them out before the first kids arrived.
Glad I noticed them and grabbed them before a kid did.

Man, I would have LOVED trick-or-treating at your house!

+1! I would love to find these in my treat bag!! Wasn't there a story a few years ago about someones ring slipping off into someones bag of treats?

 

[Rockdiamond]

Kenny, we agree on some of what you wrote- FCDs are not cut purposefully to leak light- and we agree that is not how they work to show color. By the way, different colors require different techniques if cutters want to bring out the color.
However you're still touting "light performance" as though it's a scientific measurement with regards to Fancy Colored Diamonds, it is not. It is a matter of preference.
After looking at thousands of stones you can gain a reference as to how color and cut work together- or don't- to make a Fancy Colored Diamond desirable.
Different cutters use widely different styles of angles and facet placement.'This has the effect of making one radiant or cushion look almost nothing like one from a different cutter.
I strongly believe that taking this term "light performance" out of context ( such as when using it to describe FCDs) is a disservice to diamond education.
Each diamond has an optical signature- each one has it's own light performance.
You may not love the performance of a diamond that I do, and vice versa- yet both may be well cut, as it applies to FCD's