Measuring Light Return versus Grading Light Return

[oldminer]

We often see people shoppng for a diamond with high or "highest" levels of light return. They seek out such diamonds in the hope that a diamond providing a very high level of overall light return will be also highly attractive. I think for most people, this probably will be a correct assumption although a great deal of how pretty a diamond looks is found in the cutter''s art and not simply just a physcial measurement of light returned to the eye.

It is easy enough to build a simple device which can measure some version of average light return. With such a tool one could say one diamond is brighter than another or darker than another. One could report the relative gray scale of compared stones in a numerical manner on 8 bit gray scale of 0 to 255. 0 is total blackness and 255 is total whiteness. It is easy enough to set up a small, square mirror a constant distance from a camer lens, light it in a constant manner and adjust the lighting that nearly 100% of the light return does not overstimulate the camera''s sensor. Using the same settings, limage one princess cut and then another. Crop the stones away from any visible background and look at the histogram for average light return. You will then be very able to discern which has a higher or lower average total light return. Simple enough, but not a grading standard or readily used by any other lab since the setup is only a homebuilt, one off design. However, the user could make some pretty good comparisons of diamonds which could be cropped and compared.

To bring such a simple solution to the mass market and to foster a grading standard is a far larger undertaking. There is no consensus on the standard lighting setup, but someone knowledgeable needs to build many units all the same to get things going. The comparison of gray scale numbers becomes more meaningful if folks at any place in the world ge the same gray scale readings on the identical stones. Still, there is no standard for creating grading from this.

Grading is a human endeavor placed over factual data. Grades are derived from human observation. Setting where excellent departs from Very Good, or Very Good departs from Good, etc. is absolutely a human endeavor, not up to technology.

The process of giving gray scale readings of light return is definitely with us. There has been human study of the results to create the existing grading, but grading is continually subject to further refinements. The old AGS system has been replaced with the new AGS system. The old GIA system now has a new system. While we use these systems today, there are few people who don''t think we can eventually do it better.

The measurement of light is one thing. Grading light is another. I hope the distinction is made more clear for the interested parties.

 

[Garry H (Cut Nut)]

I would just add one additional thing to that Dave.

When testing a grading system with actual diamonds, I suggest testing the worlds worst looking stones, because they are a better calibration then the worlds best.

For example does system XYZ downgrade a fish eye appropriately? Or does it capture the ugly effect of a zone of darkness from head obstruction that sits right beside a zone of darkness from leakage?

 

[oldminer]

I agree that testing narrowly won''t give the sort of results to determine how to set grade borderlines without using some of the worst possible diamonds. Of course, the entire market we see on Pricescope is highly concerned with defining the best stones. The highest value diamonds are of the most interest to dealers and consumers alike. It is very difficult to convince sellers of poorly cut diamonds to pay anyone to grade them to highlight their poor performance as well. With numerical, repeatable results, one can begin the difficult political process of setting Internationally accepted Standard Grades. The grades we do provide today are the best we can offer now, not those we envision possible.

The financial considerations are a major reason progress has been at a snail''s pace. It suits the majority of sellers to promote wide categories of "BEST" with little direct evidence of how the grade was determined and where it ends and goes into the next lower grade. AGS has not found a home for AGS 1 or AGS 2 diamonds, which, in theory, look very nice and would be a good value for money, too. It is very hard to shove facts down the throats of those who simply prefer not to base grading on facts.

Patience is the byword.

 

[Garry H (Cut Nut)]

Dave I do not imagine anyone will want to grade lousy cuts.

But this is the best test for any grading system

Grade the grader testing

For example I seem to remember an instance where Rhino "saw the light" and changed his religion from Brillaincescopanity to GIAanity. He tested one of the GIA master stones on the Bscope - it scored badly (rightly so) in GIA''s study, but did well on the Bscope

 

[strmrdr]

No absolutely not, the diamond with the best light return is not always the most beautiful diamond!!!
With rounds it comes close but putting fancies in the mix and it is totally WRONG!!!
Using the B-scope and even ASET(to some extent its very useful but not the final answer!!, it is kewl for showing patterns under 30 degree obstruction) to select asschers will lead you down the wrong path!!!

Dave please please please be careful making comments like that!!!!
We both know better and while I know what you were trying to say be careful!
Thanks!!!

 

[oldminer]

I cannot say that the highest light return equates with the most beautiful looking diamond. What is most beautiful is up to human perception, not any device. What we can say is which diamond returns more light and has a more, or most, effective cut for doing exactly that, Light Return.

Strmrdr, you are reading into what I wrote something I never said. A mirror with nearly 100% light return would not make a pretty diamond. At some point, if some cutter created a diamond with too much light return, and folks judged it less pretty than others, the grading would look like a bell shaped curve, not a line into infinity. Please don''t think I am so simplistic as to imply more is better without smart qualifications.

The RED TYPE is screaming! I think you had too much coffee, maybe

 

[susi]

Dave, I have a layman''s way of looking at mounted stones in a store. Wearing my AGS 0 ( HOF RB ) ring I put the store ring on my finger next to it, and cup my hand around both. My stone shines like a headlight in low light and it''s fun to compare with other stones.

This process looks funny, but it''s an interesting way I''ve found of getting an idea of the light return on store stones especially when the sales people are not familiar with what I''m asking them about.

 

[oldminer]

That''s a good idea you have with using your eyes as comparison tools for lgith return and beauty analysis. You have created a standard lighting environment for yourself which you can repeat.

 

[Garry H (Cut Nut)]

Date: 11/26/2007 8:06:53 AM
Author: susi
Dave, I have a layman''s way of looking at mounted stones in a store. Wearing my AGS 0 ( HOF RB ) ring I put the store ring on my finger next to it, and cup my hand around both. My stone shines like a headlight in low light and it''s fun to compare with other stones.

This process looks funny, but it''s an interesting way I''ve found of getting an idea of the light return on store stones especially when the sales people are not familiar with what I''m asking them about.

Actually you have probably found a cupping format with your hands and lighting that favours your stone.

So as i mentioned above, this will only test against one type of cut.
If you found a better stone than yours it would probably score badly in that lighting format, but may outperform yours in some others.

As Dave said - it is not a simple problem