Flourescence based on chromaticity diagram

[kevinraja]

We all know "Blue" and "Yellow" are complementary colors. Refer to the chromaticity diagram in the following link if you didn''t know that.

http://www.cs.rit.edu/~ncs/color/a_chroma.html

Simplifying the 2-dimensional chromaticity diagram into 1-dimensional diagram requires transforming it into a real line with negative axis representing YELLOW and positive axis representing BLUE, with zero in the real line being the WHITE color.

STRNG_YELLOW YELLOW FNT_YELLOW WHITE FAINT_BLUE BLUE STRONG_BLUE

-10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10

Z Y X W ... T S R Q P .. K J I H G F E D C B A


White is the meeting point between Yellow and Blue. The effect of blue flour on an yellow stone is like adding positive number(blue) with the negative number(yellow) and interpreting the resulting sum.

1. If the resulting sum is negative (but greater than the previous negative number), then your stone improved a few grades visually (eg: H color with faint blue flour ~ G color, say).

2. If the resulting sum is, say, zero, then your stone looks colorless (D, ideal case, even though as per theory, it should be A-C which in practice doesn''t exist).

3. If the resulting sum is +ve, then your stone looks bluish. Example D-F stone with Strong blue flour.

That is my penny''s worth of contribution. Hope it helps.
--------------------------------------------------------
-Raja
http://www.rasoni.com/raja

"Performance is everything, potential is nothing." - Bill Parcells, Coach of the Dallas Cowboys

 

[Garry H (Cut Nut)]

Lovely approach Kevin.

But a couple of problems:
A-C never was meant to exist - D IS colorless.

D-E-F has less color drop than J-K

Your idea only holds true if there is sufficent UV light in the environment

VStB needs a lot of UV to make it look blueish
A blueish colorless is largerly considered to be favorable - blue white is whiter than white (Lever and kitchen detergent adverts)

 

[windowshopper]

thanks Garry................whew i was starting to become delirious

 

[valeria101]

Not to mention that Blue+Yellow does not look white

You get a cold gray (a colored gray - as called) out of it.

And... those color grades are already hard enough to see. Looking for the slightest shift due to fluorescence only accounts for more eye strain. But down below M and into fancy yellow strong fluorescence makes for some obvious color change. Pretty cool, IMO.

(edited to add after the comments of Marty Haske: the image below is made by modifying the photo of a Y-Z color diamond, not by exposing the stone to UW.)

 

[mdx]

Hi Ana

That''s a really nice illustration

Johan

 

[Garry H (Cut Nut)]

Hmmm
I don''t agree Ana

I think you will find the color is often a pure complimentary subtraction because the absorption is at exactly the same frequency as the fluorescent excitation.

We need Marty here to help explain this.

 

[valeria101]

Date: 11/26/2004 5:55:8 PM
Author: Garry H (Cut Nut)
Hmmm
I don''t agree Ana

I think you will find the color is often a pure complimentary subtraction because the absorption is at exactly the same frequency as the fluorescent excitation.

We need Marty here to help explain this.

May I agree with your disagreement ?

What you mention is basic physics - nothing to disagree about.

... the post above comes from a course of design, not of physics. It took me a bit to understand the relation between the two after your post Garry. Never quite bothered with it before.

 

[RockDoc]

As with most diamond characteristics..... each diamond is unique and how it reacts or appears with varying light conditions is something an expert eye should examine.

There are some stones of medium fluoresence in which the fluoresence is a detreiment to its appearance - others with extremely strong fluoresence show no affect except under UV.

Some of this result is affected by the cutting and proportioning as well as shape.

Hope this helps,


Rockdoc

 

[adamasgem]

Date: 11/26/2004 5:55

8 PM
Author: Garry H (Cut Nut)
Hmmm
I don''t agree Ana

I think you will find the color is often a pure complimentary subtraction because the absorption is at exactly the same frequency as the fluorescent excitation.

We need Marty here to help explain this.

Gary, you rang?

See http://www.gis.net/~adamas/giafluor.html

Basically, the added blue in the 415-460nm band created by blue fluorescence offsets the yellow body color of the stone and it appears more white

Colorimeters which do not take care to eliminate the UV content will give better color grades for fluorescent stones. BUT the problem all bulbs have differnt UV content and when you pump in varing amounts of UV you get different percieved colors. A strong blue can be overgarded in color by 2 to 3 color grades..

 

[adamasgem]

Date: 11/26/2004 9:57

1 AM
Author: valeria101
Not to mention that Blue+Yellow does not look white

You get a cold gray (a colored gray - as called) out of it.

And... those color gardes are already hard enough to see. Looking for the slightest shift due to fluorescence only accounts for more eye strain.

But down below M and into fancy yellow strong fluorescence makes for some obvious color change. Pretty cool, IMO.

Nice pic.. gray is actually a tonal variation on white.. Stone is whiter..

 

[valeria101]

Date: 12/3/2004 12:51:39 PM
Author: adamasgem

Nice pic.. gray is actually a tonal variation on white.. Stone is whiter..

Sure, this is exactly why I took back the silly art class comment.

The bias of that type of material (link to sample) does seem to have a practical side: paint colors are concerned with the visual appearence of solids, not transparent material as diamonds. And again, practically, once you do get a neutral gray there is no practical way to adjust tone. With transparent material all that's needed is to turn on some light.

Not that any of this has much to do with diamond aestetics. But it is often mentioned that inclusions "help" the strength of color in gem material - especially hazy inclusions like this:

Not that anyone wold waste wisedom on severely included diamonds... perhaps fancies though?

 

[adamasgem]

Date: 11/26/2004 5:55

8 PM
Author: Garry H (Cut Nut)
Hmmm
I don''t agree Ana

I think you will find the color is often a pure complimentary subtraction because the absorption is at exactly the same frequency as the fluorescent excitation.

We need Marty here to help explain this.

Gary, I can''t explain or support your explanation because it is wrong..

Long Wave UV excitation is typically at 365nm and the EMISSION of blue light due to fluorescence is in the visible in the approximate 415-460 nm band..

 

[adamasgem]

Date: 11/26/2004 9:57

1 AM
Author: valeria101
Not to mention that Blue+Yellow does not look white

You get a cold gray (a colored gray - as called) out of it.

And... those color gardes are already hard enough to see. Looking for the slightest shift due to fluorescence only accounts for more eye strain.

But down below M and into fancy yellow strong fluorescence makes for some obvious color change. Pretty cool, IMO.

Thinking about it, I would say that is the best picture I have ever seen regarding the fluorescence in diamonds issue.
I never had a X-Y-Z with VSB that I could take a picture of like that

I asked Ana to take pics of the same stone with differing amounts of UV by moving the UV source away from the stone, what color grade do you want to get..

Those are the type of pictures that would be interesting to show a civil fraud jury..

Sometimes makes you wonder how much the value of the DeBeers stockpile rose after GIA changed their 50 years of teaching that "Diamonds should be graded at their poorer color, under artificial light devoid of ultraviolet"

 

[valeria101]

Date: 12/4/2004 11:41:34 AM
Author: adamasgem

Those are the type of pictures that would be interesting to show a civil fraud jury..

I know.... but perhaps not that one ! It is not what it seems. Please accept my apologies and have the offending exibit removed.

I can only hope it is obvious that I had no intention to misslead. The respective picture is done not by exposing a diamond to UW, but by exposing a diamond photo to (very rough) color editing. The post was dropped casually with no specific consequence in mind, I am very sorry it had unpleasant ones.

 

[adamasgem]

Date: 12/4/2004 1

6:57 PM
Author: valeria101

Date: 12/4/2004 11:41:34 AM
Author: adamasgem

Those are the type of pictures that would be interesting to show a civil fraud jury..

I know.... but perhaps not that one ! It is not what it seems. Please accept my apologies and have the offending exibit removed.

I can only hope it is obvious that I had no intention to misslead. The respective picture is done not by exposing a diamond to UW, but by exposing a diamond photo to (very rough) color editing. The post was dropped casually with no specific consequence in mind, I am very sorry it had unpleasant ones.

Apologies accepted Ana..

I''ve repeatedly seen 3 to 4 color grade shifts in VSB diamonds, but trying to find a diamond in the x-y-z range that had very strong blue fluorescence as an exemplar to buy and to photograph is difficult, as these are usually not listed on the wholesale sites or even sent to a lab for grading..