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HCA vs. BScope

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Binister

Rough_Rock
Joined
Mar 3, 2003
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16
Looking for opinions on which tool (HCA or BScope) people would be more inclined to base their opinion of a diamond on (assuming you can''t see it for yourself.)
I plugged the numbers of two diamonds I am looking at into the HCA and one scored a .8 with Excellent scintillation and the other scored a 1.4 with a Very Good for scintillation. Yet when I look at the BScope results for the two diamonds the one with the Very Good HCA score blows the one with the Excellent HCA score out of the water when it comes to scintillation.
I realize both tools aren''t the only thing a person can use to compare diamonds but I was just curious as to which one people would give more weight to when comparing diamonds...
 

optimized

Shiny_Rock
Joined
Dec 28, 2002
Messages
306
Hi Binister,

Stu's suggestion to check out the thread above is indeed good, but I also have a few thoughts to throw into the mix, some of which are covered in the HCA/BScope thread and some of which aren't.

The HCA is often described as a good tool for "preliminary screening" of diamonds. What that statement is meant to convey is that the HCA is a valuable resource when trying to get a feel for which stones will likely perform well/poorly. The chief benefits of the HCA are that it derives its ratings from data that is often available to the consumer (angles and proportions), and that it uses a more refined mathematical model that takes into account variances in proportions and angles more reliably than the typical static "AGS-style" cut ratings. But, it is definitely limited by the fact that it is only taking into account a few key numbers in order to assign its rating.

The BrillianceScope is, in theory, a great tool for getting more of a "real world" estimate of a diamond's performance, but it too has its weaknesses. Essentially, the BScope moves a light source along a predetermined arc across the face of the diamond, and takes digital images of the diamond at five predetermined positions along that arc. It then calculates the amount of white/colored light present at each position by counting the number of "white" pixels and the number of "colored" (luminous non-white) pixels. These values are used to determine the bar graph ratings. The difference in the pixel count from image to image is used to determine the "scintillation" value/bar. While this system is very good in theory there have been criticisms by some of it being rather simplistic in its workings, but to my way of thinking it's more of a "simple elegance" situation than a "too simple to be of value" scenario. More bothersome though are the occasional comments from folks who have suggested that the BScope is able to be manipulated by unscrupulous dealers to give better ratings than it should. While I haven't ever seen anybody come up with a "smoking gun" example of this allegation, it is worrisome nonetheless.

can be very useful, as well as Hearts and Arrows images (if you're inclined). And, let's not forget the value of closely examining Sarin/Megascope reports to check the consistency of a diamond's cut. All of these things are useful.

thread for some more analysis of the strengths and weaknesses of the tools we've been talking about.

-Tim

[/u][/u]
 

barry

Shiny_Rock
Joined
Mar 21, 2001
Messages
441
Tim;

You make some excellent points.

All of these tools have their strengths and weaknesses.
Consumers should employ all available tools
to base their decision.

HCA, BrillianceScope, MegaScope/Sarin with detailed Cut
analysis, Idealscope, digital photos under
several magnifications and light conditions.
In addition, consumers should talk with the vendor
regarding the diamond. Specifically, if the stone is of
SI clarity, the vendor can examine the diamond for the client and "map" the nature, position, color, and
reflectivity of the inclusions and give life and aid
in the interpretation of data generated by the above tools.

Insofar as the BrillianceScope is concerned, I would reiterate that consumers should primarily focus on
the 5 light images generated by the machine.
It is here that one can assess the amount,
intensity, and distribution of light emanating from the diamond.

Barry
www.superbcert.com
 

michaelgem

Shiny_Rock
Trade
Joined
Feb 26, 2003
Messages
372
Tim and Barry,

Re Tim's statement: "Essentially, the BScope moves a light source along a predetermined arc across the face of the diamond, and takes digital images of the diamond at five predetermined positions along that arc."

As someone very familiar with the workings of the BScope, I am cognizant of its appeal and its shortcomings.

As an important point of correctness, the ring light source does not move along an arc across the face of the diamond. It simply moves along the axis perpendicular to the diamond's table, between the camera lens and the diamond. The lens shoots the diamond's pics along this same axis through the center of the ring light.

This is important to understand, because this system evaluates the diamond only in the face-up position with a radially symmetrical light source. Many argue, rightly or wrongly, that a measure of brilliance, fire or scintillation should include viewing angles other than just this one salient viewing angle. Others say realistic light sources are not symmetrical.

I think this comment by Barry is particularly insightful:

Barry's statement: “Insofar as the BrillianceScope is concerned, I would reiterate that consumers should primarily focus on the 5 light images generated by the machine.
It is here that one can assess the amount, intensity, and distribution of light emanating from the diamond.”

Barry's exhortation to focus on the 5 snapshots accords with my research reported in "Diamond Brilliance" at www.acagemlab.com. Look at the ‘view more highlights’ section: WLR Averaging Verses 'Snap Shot" Analysis of Brilliance.

Here I point out that averaging to measure the diamond's brilliance
"has lost the detailed knowledge of the relative brilliance occurring at any particular angle of observation such as the most important face-up position. Additionally, WLR has averaged out and lost the detailed information of the relative brilliance emitted at each point across the diamond's surface. 'Snapshots' retain this detail and can individually be used to assess brilliance at each point on the diamond and each viewing angle."

Check it out and let me know if you agree, or did I just confuse the issue for you?


Michael Cowing
www.acagemlab.com
 

barry

Shiny_Rock
Joined
Mar 21, 2001
Messages
441
Very informative, Michael;

Along these lines, I would propose to Gemex that they
emphasize the images by reversing the
positioning of the bar-graphs and light images,
with the light images on top and the bars underneath.

Barry
www.superbcert.com
 

Mara

Super_Ideal_Rock
Joined
Oct 30, 2002
Messages
31,003
From a consumer perspective....when viewing the 5 different light images--it is hard to tell what you are seeing. Can someone give us a breakdown of the 5 images and their 'contents'. For example...sometimes in image #1 I may see flashes of white bright light and #2 has more fire..but I have also seen that reversed. What exactly does that mean? If once is considering each of the 5 images separately and then as a whole, what do they look for?

This is an interesting post to follow as I personally enjoy the Bscope and the information it can convey, however it seems very objective on how to process that information--leading some to question how useful that information is to the consumer.
 

optimized

Shiny_Rock
Joined
Dec 28, 2002
Messages
306
Michael,

Thanks for clarifying the nuances of the BScope's lighting method. Does anybody know if any pictures of the innards of this device exists? The Gemex site is notably short on this sort of information.



Mara,

I knew I'd read a post by Jonathan giving a bit of detail about the light views. It took a while to find it, but I prevailed in the end.


" :

~ ~ ~ ~ ~

"The B'scope also shows what crown/paviloin angle combos are flattered in certain light positions as well so long as light is being reflected out of the stone. For example shallower crown angles coupled with a shallower pavilion are flattered most in light view 1 (particularly at the arrow heads) while moderate crown angles and moderate and more traditional ideal pavilion angles are flattered most in light view 2 (particularly at the arrow heads)."

~ ~ ~ ~ ~

Maybe Jonathan can add some more detail to this information as well.

-Tim

[/u]
 
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