Help in choosing the center stone with 5.8 HCA

[jramy278]

Hello PS-ers!

I have been recommended by Pearlman's the following center stone:

A round cut 3 Ex diamond (.7 Carat, Color- I, VS2) for ~$ 2250 that is GIA certified (please see below for details):

Depth: 62.5%

Table :58%

Crown: 34 degrees

Pavilion: 41.6 degrees

Based on the above parameters, the HCA score comes out to be 5.8!

I understand that the HCA score (of less than 2) does not solely determine if a diamond is good or not and hence would like your expertise on this. Do you think it would be worth it to purchase the diamond and have it examined by Pearlman's (as they are well reputed)and then decide whether to go with it or not?

Thanks a ton!
P.S: Ideal scope and Aset images currently not available.

 

[diamondseeker2006]

I sincerely love Pearlman's, but I just couldn't spend thousands on a diamond and not get one that is in the best cut category. I mean, why pay for GIA Excellent and not get one of the better cut ones? It's a little on the deep side and that may affect the diameter, but you didn't include that number. I'd ask them to source you a stone that is within these parameters:

table: 54-58

depth: 60-62.3

crown angle: 34.0-35.0

pavilion angle: 40.6-41.0

Those numbers will generally get you into the best range of GIA Ex cut stones.

 

[jramy278]

Thanks so much for your prompt reply! I really appreciate it. Sorry about not including the measurements of the stone.
It is: 5.68-5.69x 3.55.

I am really confused at this point as I have seen people say high HCA scores are still great diamonds and Pearlmans seems to think its a very well cut diamond and worth looking into.

 

[JulieN]

What happened to the last one you posted about?

 

[msop04]

Thanks so much for your prompt reply! I really appreciate it. Sorry about not including the measurements of the stone.
It is: 5.68-5.69x 3.55.

I am really confused at this point as I have seen people say high HCA scores are still great diamonds and Pearlmans seems to think its a very well cut diamond and worth looking into.

I started a thread on this very topic... you may want to have a read. I agree that a >2 HCA does not mean it can't be beautiful, however to score a 5+ seems iffy to me. Hopefully, one of the more seasoned PS members will chime in...

https://www.pricescope.com/community/threads/hca-2-0-but-still-performs.192820/

 

[msop04]

To make it a little easier, this is the response from Jon at GOG:


by Rhino » 27 Aug 2013 19:22

I have seen *many* that scored over 2.0 that were just fine, particularly when the HCA was geared to kill diamonds that hit the 41.0 pavilion angle mark. I've fielded so many questions on the technology I was forced to write an in depth article on the subject that I could refer people to so I wouldn't have to type it out each time.

This however was from a cutting facility that consistently produced precision cut diamonds utilizing a 34.x crown angle (sometimes 35.0) and were always superior Optical Symmetry Hearts & Arrow diamonds.

Garry and I are among a handful of gemologists who truly grasp and appreciate reflector based technologies and the HCA rightfully does ding diamonds with the 41.0 pavilion angle as it is a threshold angle that generally = blatant light leakage in round brilliant cuts under the table and on the lower half facets. I generally have referred to this in the past as the "ring of death" in previous posts.

The thing is this ... diamonds with 41.0 pavilion angles can be just fine however the *saving grace* that I have seen was superior or near superior Optical Symmetry (ie. H&A patterning) in precision cut diamonds. The fact that it was dinging perfectly fine diamonds (even under the FireScope which was the primary tool used to develop the HCA) disturbed me. Garry has since made adjustments and last I checked seemed pretty good although I don't use it today to make my buying decisions.

To consumer's I'd counsel this ... if a diamond does score over a 2.0 on the HCA but the seller *swears* it is just fine ... ASK FOR PROOF. If the diamond does indeed have a genuinely solid FireScope/IdealScope/DiamXray result there's your proof. Otherwise ... proceed with caution.
Kind regards,
Rhino

 

[jramy278]

Thanks for your responses.
JulieN - Both of the last 2 stones had a slight brown tinge to it (as told by the vendor to PJ) and so we decided not to go with them.

msop - Thanks for the links and Jon's post. I noticed one PSer talked about a great diamond with > 5 HCA as well. And all the vendor posts (Jonathan, Wink etc) all say they rely on their eyes 1st and HCA last (if at all)...It's all so confusing! PJ assures us that he will take a look at the stone in person for us to look at symmetry, and says that a GIA triple ex will never have leakage issues (in all his years of experience and always satisfied customers etc). Argrghhhhh

 

[pyramid]

Just wanted to write this. It seems very strange that for years on Pricescope, customers and vendors have been saying how great the HCA is, and now there has been a sudden turn against it. People saying in this thread that the vendors Jon and Wink use their own eyes and then maybe the HCA if at all. I have also read recently that the HCA is not known at all to the public. Why is it then that Garry Holloway is mentioned in write ups by GIA and thanked for his help in their large cut study. I also read a thread where another vendor seemed to be having a pop at Garry and discrediting him. This vendor is a very well liked one and not one I would have expected it from so don't really know what was going on as the discussion was a bit technical and maybe they both had just reasons for the bit of an argument. It seems really weird how things have all turned all of a sudden. I have been on this board for years and it seems that there is no real technical education anymore and it is all going back to the way it used to be, buying with your eyes.

Is it because people are buying more old cuts now that the vendors want people to just go with the flavour (another word used a lot here now is personality - never mentioned on pricescope before) of the old cut diamond and technology is being discontinued and not encouraged anymore?

Garry's ideal scope does still seem to be praised but there is a bad feeling here now about the HCA. I just remembered that I read it on another board about no one knowing about Garry's HCA in the real world and that the person writing it did not recommend the HCA. This person who wrote it is an appraiser here on this board. It seems kind of in bad taste the way Garry is being treated. He was always very helpful to customers and a nice personality to have around, with great jokes/humour.

 

[jramy278]

Thanks for your post Pyramid. I'd like to clarify that I was simply paraphrasing some other posts and not trying to discredit or offend anybody. I'm really new to all this and am simply trying to learn so I can make an informed decision. I apologize if my posts have indicated otherwise. I have great respect for all of your knowledge and expertise, that's why I'm here in the first place

 

[JulieN]

I'd rather have a brown I than a 5.8 HCA.

 

[MissGotRocks]

The HCA should be used to weed out questionable stones - not pick the winners. I think the thought process goes that if a stone scores 2 or below on the HCA, it is a stone worthy of further consideration. I think it has been very useful to many people but it is a start rather than an end.

AGS0 grading trumps the HCA because they have actually seen the stone and performed assessments on it. The problem with the stone the OP posted is that it has a pavilion angle of 41.6 - the HCA sharply dings stones with a pavilion angle above 41. It could be a very pretty stone and it could meet his requirements but like DS, I would want a stone that gets AGS0 or GIA3x.

I personally would always use the HCA for stones that I was considering when dealing with only the numbers. I think it is a pretty reliable tool but nothing beats some of the light performance assessments that can be performed on an actual stone. I do not think the public at large is aware of the HCA but I also know much of the public is not aware of ideal cut stones either. We know that based upon the people that still come here for help - and I was one of them yay long time ago! Thank goodness for PS, Garry Holloway, the HCA and Dave Atlas and his diamond guide. These are some of the great things that you can access right off the bat to assist in beginning to understand the difference between a well cut stone and a not so great cut stone!

 

[jramy278]

Thanks MGR. I just wanted to point out that the stone I posted IS a GIA3X. I'm still a bit confused, would you (/others) recommend we bring the diamond in to take a look, or just pass it over and keep looking?

 

[jramy278]

Also can someone help me with understanding this a little better? It seems to me that the depth (62.5%) and the pavilion angle (41.6 deg.) are the proportions that are out of whack. So this combination is a problem because there can be issues with the light leaking out of the lower part of the diamond instead of being reflected back through the face? What does this look like in real life (i.e. if I was to order this diamond and then go take a look at it, what am I looking for that indicates if it's a good/bad stone)?

 

[pyramid]

Thanks for your post Pyramid. I'd like to clarify that I was simply paraphrasing some other posts and not trying to discredit or offend anybody. I'm really new to all this and am simply trying to learn so I can make an informed decision. I apologize if my posts have indicated otherwise. I have great respect for all of your knowledge and expertise, that's why I'm here in the first place

Hi jramy278

No I am not against what you have written at all, I know you were repeating the information you were given, I would have done the same. I am just wondering what is going on with the change of opinion on the HCA. I know it was a tool for sifting through worse looking diamonds to discard them, but most people and experts seemed to see it as good for that purpose. Something has now changed here. I wouldn't pick a stone which is over 5 on the HCA. If there is a reason it is good though or even if Garry Holloway could explain why it may be good, then I would maybe change my mind, but not having that information I would look for another stone rather than regret buying if I saw a better more sparkly stone in real life later on.

Maybe it is just that the experts are now going with the laboratory grading i.e. GIA saying it is Ex Ex Ex or AGS saying Ideal and have no use for the HCA anymore, it is always preached we should go for the top cut and not even a GIA Very Good. Why this so when a M or N diamond is praised and an old cut with no cut grade too. Is there two camps here now, the old cut brigade and the Ideal/Excellent brigade and Garry's help to find for example shallow earring/pendant stones that face up bigger and the dirt does not adhere to them so badly is now redundant. So nobody buys a modern cut unless it is Ideal or Excellent anymore or they are buying from a bricks and mortar store. Is this the internet trying to flush out local stores like the supermarket chains have done?

 

[kenny]

Reject rounds with HCA scores over 2.

Get Idealsope pics on rounds that score under 2.

Compare them to this.



This easy 2-step process guarantees a well-cut round.
It may reject a few rounds that experts with years of experience would not have rejected but who cares?
You and I are not experts with years of experience.

 

[AprilBaby]

I would still try to stay under 2.

 

[Gypsy]

MO, we've talked about this many times.

Under 2 if you have no idealscope.

Up to 3 if you do, is fine.

2-3 range has a LOT of nice stones and if you have an idealscope, you get everything you want there.

But if you do not have an idealscope then under 2 is safer.

All scores under 2 are equally good.