Question for Chan and whomever else may know...

[gee5088]

Hello Chan,

In a reply you made earlier today to a question from peptidbond, you noted that a stone with a lower score on the HCA (below 1 specifically) would appear "more brilliant than firey". Could you elaborate? By firey do you mean more flashes of color? I've been lurking for a few months now and we'll be purchasing a stone with an HCA score of 0.7 (EX/EX/EX/EX). It's an AGS Ideal
1.03 ct F/SI2 (eye-clean) and am now wondering should we be concerned with this lower score? I've read much and I know for some a score between 1-2 is ideal but still don't fully understand why. Please help! Thanks in advance...

 

[chantheman]

Let me preface this by saying that I am not an expert. I am relying on the explanation provided by Gary Holloway in the HCA tutorial. It will also provide some information about the differences between TIC (Tolkowsky Ideal Cuts), BIC's (Brilliant ideal Cuts), and FIC's (Firey Ideal Cuts). The reality of this situation is that there are many things that can affect the level of fire eminating from a diamond. The diamond My fiance' has scored a 1.4 on the HCA, yet I still see quite a bit of brilliance.

Hopefully one of the real experts will post some information here as I, like you could surely use some additional specifics. Most likely it is related to an area of physics that is far too complicated for me to understand.

Per Gary's Tutorial

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"Stones near the center of the red region, those with the lowest scores, are often the least affected by small symmetry variations.

A shallower stone, on the lower part of the chart, will look darker when viewed from close up, they are not for everyone. Shallow stones have the advantage of a bigger spread. They are better suited for use as pendants and earring stones where they are not usually viewed from very close proximity (a close observers head obstructs light sources that would otherwise be returned).

Deeper proportioned stones, near the upper part of the red area, have more leakage. Leakage means reduced light return. A limited amount of reduced light return can contribute to a diamonds contrast. Diamonds with a large area of partial leakage table, seen as a pale pink area with an Ideal-Scope, are best set in open backed rings so light can get in the bottom or pavilion of the diamond. It is possible for light entering the pavilion to leak back out the top as firey dispersed colored flashes. Deeper diamonds that have perfect or hearts and arrows grade symmetry, with scores around 2, will often perform far better than diamonds of lesser symmetry."
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The reality of the information above is that there are a multitude of interelated factors that feed, at varying levels into the HCA score. Surely there are stones in the market that score a low HCA that have a great deal of fire. Also, as can be seen with Mara's previous diamond, a higher HCA can yield a great deal of brilliance.

I bet your .7 HCA is a great stone and quite firey. The component crown and pavillion angles and minor facet alignment factors greatly into the appearance. Venus by Infinity stones often have low HCA scores, but are obviously very beautiful stones. If your stone looks good in a variety of lighting conditions then it is most likely a firey and brilliant stone like my 1.4 HCA. It has also been posted that the typical viewer will not necessarily be able to tell the difference in sub 2.0 stones. The PS scope forums are filled with combinations of science and reality. Sometimes the hardest thing to do as a "learning" consumer is to decide where you draw the line in your decision making. This is most likely the reason all experts urge consumers to rely on their eye. I fully concur!

I really hope an expert will add to this thread. I know I have seen the brilliance vs. fire debate here on PS, I just cannot seem to remember where.

 

[pqcollectibles]

It''s my understanding that diamonds with lower scores may visually appear more brilliant due to a lower level of contrast.

Colored Gemstone Nut, aka Josh, explained contrast in a post in a thread yesterday. Here''s a link to that thread:

https://www.pricescope.com/community/threads/j-color-h-a-si1.25099/

If you''ll scroll down toward the mid/bottom of the thread, you can read Josh''s response there.

With reduced contrast, the eye will perceive more white light return, or performance described as brilliance.

Ideals can, and will score up to 2 on the HCA. Some near Ideal cuts will even exceed the 2 cut-off but will still be less than 3. Some people will love the look of diamonds that score in the 1.5 to 2+ range. Other people prefer diamonds that score near 1. The type of performance that appeals to you may not be the type of performance that I prefer. The best way to decide what appeals to you is to get out and look at diamonds. Get the stats on diamonds that you see in person and make note of the ones that appeal to your eye the most. As you view diamonds, you''ll notice a trend developing of corresponding HCA scores and the diamonds you liked vs. those that did not appeal to you. A lower HCA score, below 1, does not necessarily mean the best diamond for you.

 

[gee5088]

Thanks Chan and pqc...

I appreciate the feedback..I knew there was much more to learn!!!

 

[Rhino]

Hi PQ,

You got it a little mixed up.

Actually, the greater the contrast the brighter the diamond will be. Also ... when discussing contrast it helps to clarify whether the contrast is between light return vs light leakage vs the contrast of facets reflecting back white diffuse light vs head obstruction. One is a comparison that in my opinion degrades the optics (as in the first case a diamond may have greater contrast due to MORE LIGHT LEAKAGE), and this IMHO is a negative contrast. Why? I don''t believe a diamond should be rewarded for more light leakage. The latter is a totally different perspective which I had introduced in my studies on the subject adn published in our tutorial on it. This type of contrast compares not leakage/return but that of facets reflecting back white diffuse light vs facets reflecting back head obstruction. In this case the greater the contrast THE BRIGHTER the diamond will be ... hence greater brilliance. In this perspective 2 factors would contribute to the decrease of brilliance/contrast, light leakage contributes to the DECREASE OF BRIGHTNESS and the 2nd is too much head obstruction.

I am beginning a discussion with the scientists at AGS on this subject because if they are going to factor in a grade for brightness relating to the subject of contrast (particularly as observed in suffuse light), it is my conviction that a diamond should not be rewarded with a higher contrast score for more leakage.

While I have many positive things to say about the HCA, determining contrast is not information that can be garnered from that as the minor facets & optical symmetry play a very relevant role in determining this feature of diamond optics.

Hope that helps cel

Kind regards,

 

[pqcollectibles]

Hey THANKS, Pups!!

You really cleared that up for me and anyone else reading this post. Guess I have had it backwards all along.