A question from a Gemmology student

[Spear]

After looking at a lot of fancy coloured stones on the internet, I noticed that fancies do not display the same amount of fire and brilliance as colourless stones.

Brilliance in a colourless stone is displayd as flashes of light, while a blue stone would rather have a blue glow then blue flashes of light.

I have two theories
1. Transparency is a key component to brilliance.
Since a colourless diamond is obviously more transparent then a blue diamond, it would display a larger amount of brilliance.
2. The prism effect is when white light is separated into the spectral colours.
White light enters a diamond, it reflects against the pavilion facets, and exits through the table as flashes of white light, or though the crown as flashes of coloured light.
If light enters a fancy blue diamond.
The white light automatically changes its colour to blue.
When the blue light exits the stone through the crown, there is no fire because the prism effect is when white light is separated into its spectral colours.
Blue light canot be separated into the colours of the rainbow.
If any of you can help me understand why fancies do not display as much brilliance and fire as colourless diamonds, It would be much appreciated.

 

[Spear]

As far as my internet search is concerned, I did a google image search on the hope diamond and the de young diamond.
I could see no brilliance or fire, but i did notice that on these two stones there are blue or red spots and darker(black) spots.
What is the cause of this?


I still have lot of mountains to climb before I can understand diamond cut!!!!

 

[Rhino]

Hi Spear,

Welcome to the forum. Your thoughts/theory on why brilliance isn''t as intense in fancy colored diamonds (particularly those of the intense/vivid classification) make alot of sense. I''ve sold some fancy colors in my time but have never really studied them as *intently* as I have with colorless, near colorless and tinted stones. My general observation has been that if they emitting anything it''s white light and as you note ... little to no fire. I''d want to see and anlayze more before I made any kind of a judgement call though.

Regards,

 

[Rhino]

Date: 5/8/2005 5:43:37 PM
Author: Spear
As far as my internet search is concerned, I did a google image search on the hope diamond and the de young diamond.
I could see no brilliance or fire, but i did notice that on these two stones there are blue or red spots and darker(black) spots.
What is the cause of this?


I still have lot of mountains to climb before I can understand diamond cut!!!!

Let''s see the pic and we''ll give ya some input.

 

[Sunni79]

I have a fancy light yellow diamond and in my opinion, it displays as much fire and brillance as a colorless stone. I thought fire and brillancy came from the cut of the diamond anyway.

 

[Garry H (Cut Nut)]

Color is caused by asorption of certain wavelengths (colors) that leave us only what is left - sere is less visible light emerging from any colored material or even a surface.

Yelow diamonds have blue absorption.
Blue diamonds have yellow absorption.

The more absorption, the darker the stone.

I do not like red diamonds as much as strong but mid purplish pink diamonds because the reds have less light return. But reds can be 10x the price.

 

[Lord Summerisle]

And isnt there also a trend in fancies to cut to show off the inherent colour of that rock.... at the expense of light return?

 

[Garry H (Cut Nut)]

Yes, me Lord

But this is mainly for very pale colored diamonds to make them look deeper in color - radiants are a good example - they tend to extend the light paths for a couple more bounces - this is like the full vs half full glass of flavoured colored water effect.

Well cut round brilliants can decrease the effect.

 

[oldminer]

Brilliancy, light return, will be decreased not by color so much as by the tone of the color. Tone is the steps of white into black. Gray tones are the intermediate steps. The less pure,, full spectrum, white light, coming back to the ley, the less brilliancy. As gems become more dark in color, they become darker in tone.

You can have fancy colored diamonds with very goodbrilliancy because they really are not all that dark. Very deeply colored gems will have less brilliancy.

Some stones with highly saturated colors, but light in tone, will have high brilliancy. (Fany color diamonds in the yellow colors are an excellent example)

Spectral disply, known as fire, will decrease as stones become darker. If one was to measure the fire in a dark blue stone, very little of the other colors will be found as they have been absorbed by the material. If one only measures colored light return as a measure of "fire", then the reading on a dark blue stone would show lots of faire, all blue, and be very misleading. If one eliminnates body color, then only a tiny fraction of fire would be found.

 

[aussie1]

Old miner, I sent you a e-mail and an attachment, with acouple of questions??
havung received no reply either in the affirmative, or negative, I am wondering if you received it????
Regards
Aussie

 

[Spear]

Thank you Oldminer, That really makes sense.

I looked at a lot of pictures of fancies on the internet.
I understand that it is truly an art to capture a diamonds optical beauty on camera so I decided to look mostly at pictures of famous diamonds, because it is likely for a famous diamond to have several pictures on the net so I could separate the good pictures from the bad.

I did not think of comparing fancies with different tones and saturation.

Thank you to everyone else who took the time to comment on my question.
So if a fancy’s color increases in tone, It also increases in value.
But at the same time, its brilliancy decreases, so technically it should decrease in value.
If anyone has any pictures of fancy colors displaying brilliance or fire, or lacking them.
It would be much appreciated if you could post them in a reply.

 

[valeria101]

Well... strong (saturated) color does not get rid of fire unless the material is dark as well. The cut of fancy colors cuts fire so observing such stones hardly yields good evidence of what the optics of the material really can deliver at it's best interpretation.

Cheaper gem materials with strong color and dispersion get more often cut to show best brilliance and fire since the rough is easier considered worth "wasteing" on a great cut. Think of sphene and demantoid - except for the really dark material, they can have spectacular fire. Good luck finding diamonds with similar color and great cut to complete the argument, I certainly do not have such encounters on the record

The closest example I have seen was a 30 point FVPP round ideal cut and it certainly was fiery.

Using some cut modeling software that allows to tweak absorbtion, RI and diespersion of the "material" could at least produce theoretical examples. The "Cut Adviser" by MSU allows this. And Garry said there is some versio of it that models fire as well.