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H&A + HCA

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harry

Rough_Rock
Joined
Feb 27, 2003
Messages
50
I have read a bunch on H&A diamonds and the Holloway Cut Adviser. As I understand it, an H&A diamond can still have a less than stellar HCA visual performance score due to light leakages. Conversely, a great HCA visual performance score may not have the symmetry and cut of a H&A diamond.

If the above is correct, and I purchase a H&A diamond with great HCA scores, will I have covered all my bases in terms of cut? Is there anything else in terms of cut (not the other 3 Cs) that I''m not addressing? Thanks.

Harry
 

canadianice

Rough_Rock
Joined
Feb 4, 2003
Messages
82
Harry -
Some people like to see results from an instrument called the Brilliance Scope, which measures light return from the diamond based on different light positions.

The BScope is purported to represent the stone's performance under "real" conditions (whatever those are!), and gives a readout for white light, coloured light and scintillation.

Companies like SuperbCert.com and GoodOldGold.com have an abundance of information on their stones, which you may find valuable.
 

harry

Rough_Rock
Joined
Feb 27, 2003
Messages
50
Yes, I have read about BrillianceScope. I think there was a thread about BrillianceScope vs HCA in this forum. I have also read about it in the goodoldgold.com web site. I guess I have 2 questions now.

1) If a diamond has great HCA scores, will it also have great BrillanceScope scores? If not, why?

2) If I buy a H&A diamond with great HCA scores PLUS great BrillianceScope scores, will I then have covered all my bases in terms of cut? Will I have missed anything else in terms of cut?
 

canadianice

Rough_Rock
Joined
Feb 4, 2003
Messages
82
Check the AGS"0" vs. HCA vs. Brilliance Scope thread (started by Scorpionrioux -- you can search for that author's name) that is going on right now.

A good question -- although there are lots of reasons to think a great HCA will equal a great B-Scope, that isn't always the case...

I like the sites that provide all of the relevant data, including Sarin reports and B-Scope readings, for me to make my decision.
Cheers
 

canadianice

Rough_Rock
Joined
Feb 4, 2003
Messages
82
Harry, also check out David Atlas' cut charts (Accredited Gem Appraisers) used to categorize the porportions. The Cut Grade definitions are precise and widely accepted. http://www.gemappraisers.com/

AGS also has "ideal" proportions, although these parameters are pretty broad -- an AGS "O" Ideal isn't necessarily a winning stone.

You can also buy an Ideal-Scope and check the cut yourself, as I'm sure Garry Holloway (the I-S inventor) would tell you to do...
 

niceice

Brilliant_Rock
Joined
Jan 29, 2003
Messages
1,792
We have a lot of respect for the developers of the HCA and the BS but nothing beats a good set of eyes. We've rejected diamonds for lacking in visual performance which scored great "on paper" on the HCA and kept others which scored poorly... Hey, it's a work in progress not an absolute indicator, but we would like to add that the HCA just seems to be getting better and better with time. The same goes for the BS in our opinion, it is an indicator of potential, not an absolute defining factor. A lot of the problem with the BS lies not with the equipment, but with the user and how they have calibrated the machine. Rhino will probably tell you that he's measured diamonds on his BS (which we believe to be calibrated properly if his reputation is any indicator) and they have scored quite low after they were scanned by another dealer and the score was very high... No doubt that RockDoc would back him up on this as we know that he has seen this occur on quite a few occasions. So what we're trying to say is that the accuracy of the BS seems to have a lot to do with the operator...

The fact is that the proportions and alignment of the facets is what controls the visual properties of the diamond. Get a balance between the pavilion depth and crown height of the stone and you are likely to find a diamond that performs quite well. Now we want to say that while we are referring to depth and height correctly, what we actually want you to focus on is the crown angle and pavilion angle because those measurements are actually measured by the Sarin / OGI machines and the percentage depths are estimated. So a crown angle of 34.5 degrees works really well with a pavilion angle of 40.8 degrees but a crown angle of 35.0 degrees with a pavilion angle of 41.2 degrees would probably result in a dog of a stone... And interestingly enough, the HCA will back this up. A middle of the range crown angle with a middle of the range pavilion angle works well, a shallow crown angle with a deeper pavilion works well, a shallow pavilion with a deeper crown works well, but a deep crown and a deep pavilion won't and neither will a shallow crown and a shallow pavilion... Look for a balance of the parts.

The easiest thing to do is to select a diamond within this range:

Total depth: 59 - 61.8%
Table: 55 - 56%
Crown angle: 34.3 - 34.8 degrees
Pavilion angle: 40.5 - 40.9 degrees*
Girdle: 1% thin to 1.7% medium, preferably faceted.
Culet: none or pointed (same thing, different lab description)

As stated previously, there are many other combinations of proportions that will work quite well... However, it is easier to look within this range and obtain consistent results. Now every once and awhile, we'll find a diamond within this range that just lacks the visual properties we expect from a stone... Maybe it has something to do with the internal structure of the stone, we really don't know - it is definitely not something that can be figured out "on paper". This is where a reputable seller that actually sees the diamonds that they sell is invaluable because they can reject such a diamond on your behalf and probably did from their actual inventory (as opposed to a virtual, never actually seen inventory) before you even had a chance to review the details of the stone. How can you separate the virtual vendors on-line from the vendors with real inventory? They will be the ones with clarity photographs of the stone, scans of the actual lab reports instead of a black and white copy, H&A photos of the actual stone as opposed to the generic one used in so many instances... You get the idea.

H&A is not an indicator of the visual potential of the diamond as much as the proportions are. We've seen many H&A stones that were not as brilliant and dispersive as non-H&A ideals and vice versa.

One last thought... Look for consistency of size in the crown and pavilion facets on the OGI and Sarin reports... The full reports (as opposed to the little stickers) actually show the individual bezel main and pavilion main facet measurements that make up the averages displayed on the label... In other words, the label might show the crown angle to be 34.5 degrees but tht is an average of the eight facets measured... The actual range of measurements could be as tight as 34.4 / 34.5 / 34.6 / 34.4 / 34.5 / 34.6 / 34.5 / 34.4 or it could be 34.3 / 34.8 / 34.6 / 34.4 / 34.8 you get the idea... The tighter the range, the better that puppy is going to perform... Some dealers don't know that they can display these results on the reports that they print out of their machines, so you may need to ask for them... We can tell you that the information provided on the full reports is invaluable.
 

optimized

Shiny_Rock
Joined
Dec 28, 2002
Messages
306
Hi Harry,

First off, you are correct that an H&A may not actually be cut to outstanding proportions (and may score lower on the HCA), and that there are a lot of great performers that are NOT H&A. The tendency though is for H&As to also be fairly good performers, presumably since the type of cutter whose craftsmanship produces H&As will also typically cut diamonds to better proportions. Ultimately, H&A patterns are only a concrete indicator of the overall symmetry of the facets of the diamond, and should be looked on as such.

While I really like the HCA and consider it a valuable tool, I wouldn't use it as my primary evaluation method. As Garry will attest, it is a very useful thing but it is still evolving and getting better, so is not exactly a "definitive" indicator (yet). I think it's strongest when used as a tool to dismiss inferior stones, but ultimately it can't tell you for sure that a stone is great. Like I said though, it's getting better all the time...

here at Pricescope. I'm pretty interested in what Scorpionrioux's research project turns up. You may want to check out that thread for some more information.

I can say that one thing that limits the overall effectiveness of the HCA is the fact that it is using only a few averaged numbers to make its determination (depth/table percentages, crown/pavilion angles, culet size), so is not able to get an extremely accurate picture of the diamond's proportions. This isn't Garry's or anybody else's fault, it's just the limit of the current technology. More accurate ratings would require measurements of all manner of absurdly obscure angles and percentages (main and minor facets, etc.) and would be extremely cumbersome to use. I think Garry has done a great job of making a very useful tool while requiring a minimum of "cut geek" information from the user. I dig it...


I would caution you that ALL of the tools that are commonly talked about here on Pricescope (and elsewhere) should be looked at as just that- tools. They are very helpful in weeding out poor performers, but no one tool should be relied on too heavily, and in the end it is your eyes that should be the ultimate judge.

(for another respected opinion of the proportions), H&A imagery (for overall symmetry), Lightscope images (for leakage indications) as well as digital photography of the stone itself.

But, in the end I chose my diamond because when I opened the package and looked at it I was immediately enthralled. I knew I had the right stone when I saw it light up as if powered by a small nuclear reactor within.
All of the tools were very useful in helping me make an informed choice, but my eyes were the final judge...

Hope this helps.


-Tim

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optimized

Shiny_Rock
Joined
Dec 28, 2002
Messages
306
Wow, Robin/Todd, that's eerie.. I post a reply, and you've beaten me to the punch by a few minutes AND said almost all the same stuff... Great minds think alike, eh?


-Tim
 

barry

Shiny_Rock
Joined
Mar 21, 2001
Messages
441
Calibration of the BrillianceScope is done manually
by the operator/vendor according to clear directions and
instructions set forth by Gemex. If not done properly
and on a continuous basis the internal software will disable
and shut down the machine.

After a diamond has been run, resultant images and output are
sent to Gemex for review and approval. Gemex can determine
whether the machine is properly calibrated and the stone run
correctly. If the 'run' passes Gemex's review the images are converted
to gif's and sent to the vendor for his use.
If not, the vendor is asked to re-run the diamond. Some problems that
might interfere with a clear result are lint or spec of dirt on the
diamond, improper centering, or 'planing' ( a film that settles
between the diamond's table and the glass plate of the BScope).
Problems relating to the software can be detected and are
addressed either by Gemex from their offices or through on-site
tech support. A vendor can not access his BScope data unless
it has been first reviewed, approved, and returned by Gemex to the vendor.
Gemex encourages vendors to have their results validated by a printed
Light Analysis Report.

Barry
www.superbcert.com
 
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