HCA - How much credence?

[djgaloot]

So I''m starting my e-search for diamonds. One site I''m looking at lists all the numbers to plug into the HCA. The program seems VERY sensitive to the combination of specs. How accurate are the specs given for the diamonds. I assume these are just averages. If the sarin report is available, how do you account for the symmetry (or lack thereof)? Finally, Would you even be able to tell the difference between a diamond that is the same size that scores a 0.8 Ex-Ex-Ex-VG and a 1.7 Ex-VG-VG-VG?? I realize that the HCA is not the end-all and should only be a part of the decision making process but How good is it?? should I be worried about Ex scores vs. VG scores?
thanks,

 

[Mara]

There are some posts on this in the advanced search archives, take a peek.

The HCA results should be taken with a small grain of salt, but many have found them to be pretty accurate in most cases. I think what you really should be looking for is stones that fare very badly on the HCA...chances are they are faring that way for a reason (e.g. the pavilion is too deep, crown too shallow or ?). There will be times when the HCA will not be AS accurate as it could be, but as long as you don't take the results as gospel you should be fine.

Where I would be concerned would be if the HCA returns a score over 4. 4-10 scores I would just PASS on that stone. Why bother when you can find a stone that the HCA scores under 4 or even under 3 or 2 for probably the same price? That is where you have a bit of leverage over the scores of people out there who don't know about the HCA. As Rich posted on your original post about the stone you were considering, that stone will probably have the leakage ring around the table. DiamCalc combined with HCA tends to make me a believer even though minor facets may make a difference.

To answer your last question, there really will be no huge visual difference in a stone that is .8 or 1.7. Anything under 2.0 is pretty good. But you may see a difference between .8 and 2.5...a huge difference? Maybe not. You will definitely see one between .8 and 3, or .8 and 4. Some people don't like stones that score .8 but prefer those that score 1.7 (these are people who can compare in person with their eyes). It really depends on your eyes. Our stone when we bought it was a 1.5 on the HCA and some recent changes to the scoring now made it a 2.8. Would we have bought it if it had the 2.8 scoring? Maybe not. But its very pretty in person and I get compliments all the time. So my personal preference may be for a stone under 3.0 rather than 2.0!

It's all about your level of comfortability.

Good luck!!

 

[Richard Sherwood]

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The program seems VERY sensitive to the combination
of specs.
-----------

True. This is largely because the light performance of a stone is VERY sensitive to different combination of specs.

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How accurate are the specs given for the diamonds. I
assume these are just averages.
-----------

Some labs "round off" the numbers. These are the least accurate. Some of the EGL labs come to my mind, but there could be others. The AGS doesn't, nor the AGA. The best figures to work off of are the Sarin or Megascope numbers. These are not rounded off. The figure you're looking at though is an "average", in that (for example) the angles of all the crown main facets are added and then divided to come up with the "average" angle. This usually works pretty good unless there's a large variance between the facets.

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If the sarin report is available, how do you account
for the symmetry (or lack thereof)?
-----------

The symmetry grade is a human-assigned grade rather than a machine-assigned grade, so you won't see it on a Sarin or Megascope report. A gemologist however, could get a reasonable assessment of the symmetry grade from examining one of these reports, although he probably wouldn't put it down in writing until he saw the diamond.

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Finally, Would you even be able to tell the
difference between a diamond that is the same size
that scores a 0.8 Ex-Ex-Ex-VG and a 1.7 Ex-VG-VG-
VG??
-----------

A layperson would probably never spot the difference. A PriceScope educated consumer that really knew what he was looking for might be able to. A professional diamond dealer or gemologist would be able to.

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I realize that the HCA is not the end-all and should
only be a part of the decision making process but
How good is it??
-----------

It's pretty darn good. As Mara states, you might not want to bother with stones over a 4.0 rating if a premium cut is one of your major objectives.

For internet buyers, it really helps in the shopping process. If you combine it with other tests and instruments, you can make a much better informed decision than you would ever be able to make standing at a jewelry counter and listening to the average salesperson.

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should I be worried about Ex scores vs. VG scores?
-----------

Not worried, but aware. It's all a balancing act, between size, color, clarity, cut & price. Decide what's most important to you, and use the instrumentation to eliminate the stones which obviously don't fit your parameters.

You might consider purchasing an IdealScope as well to help you in your search when you get down to the viewing stage. For $30, you get an instrument that immediately tells you if a stone is not performing well.

 

[caratgirl]

You know, I was slightly sceptical about the IdealScope when I purchased it, but what a pleasant surprise it was! It saved me from buying several inferior diamonds, and the salespeople could not get over the images. I had one shop's manager literally disappear with it and I had to ask to get it back. I was able to get a much better feel for what my eyes were actually showing me versus what the IdealScope was showing me.

Do be prepared to be disappointed in some diamonds that you may currently own, however. I have a princess cut and an oval cut .50 pendant that barely give a glimmer of pink at the center, so now I know why the lack of sparkle (fire) always kind of bugged me even thought they are very white.

On the other hand, my sparkly 1.00 tw earrings did quite well, even though they displayed no H&A or great symmetry. The proportions must be better than average.

Even though I had always wanted an upgrade, I was shocked to see how much light leakage my round e-ring diamond had! It always sparkled better than others I had seen, just not from the top, more from the crown facets. I saw this reflected in the IdealScope images perfectly.

The excellent new stone I chose from DBOF was a great performer on all the other documents and was absolutely perfect viewed through the IdealScope.

One additional perk with the IS was being able to quite easily see any flaws in the stone without going blind using the loupe. They show up perfectly in black, since of course that spot cannot (usually?) reflect light.

In my opinion, the best tool for an end-user on the market that I can totally recommend.

 

[niceice]

With all due respect to Garry Holloway and the HCA, we think of it as a "work in progress" which is an "excellent reference tool" for consumers, but one which should not be relied on heavily because we often source diamonds which scored very high on the HCA which we reject for lacking in visual performance and other times keep stones which are exploding with light, but which scored low straight V's on the HCA... And then there are quite a few which score well on the HCA and score well during our selection process... But definitely better than nothing at all for the average consumer! After all, what else do you have to go on? The HCA combined with the Ideal Scope does seem to be a powerful combination...

We recommend:

1. Search for diamonds which score well on the HCA.

2. Source that diamond from a dealer who insists on seeing the diamond prior to selling it so that they can ensure that the diamond does indeed exhibit a high degree of light return... While many of the dealers here on PS merely list diamonds for sale and drop ship those diamonds from their suppliers direct to their customers, there are others who visually inspect and evaluate every diamond that they sell to ensure the satisfaction of their customers and the integrity of their name... Those companies include ourselves NiceIce.com; GoodOldGold.com; SuperbCert.com; WhiteFlash.com; and a few others who's names escape us at the moment...

3. Be sure that the dealer provides you with detailed clarity photographs of the inclusions so that you know what to expect when you finally manage to see the diamond through a loupe for yourselves. Keep in mind that clarity photographs will not provide you with a true indication of the visual properties of the diamond and that the inclusions will look much larger in the photographs than they are in reality... You might be surprised at how often we hear that somebody is concerned about "how big" an inclusion appears in a picture because the customer overlooks the fact that they are evaluating a diamond crystal located within a facet that is pictured on their computer monitor as if the diamond was the size of a basketball... Of course the inclusion looks huge when the diamond is that size!

4. Be sure to obtain the "full page" Sarin or OGI computerized proportions analysis and not just the Avery mailing type sticker because the full page report provides much more detailed information including a facet-by-facet breakdown of the high and low measurements which make up the average for the crown and pavilion angles... The HCA becomes extremely accurate when you have this information to play with...

5. Assuming that you are not an experienced diamond grader, be sure to have the diamond verified by an independent GIA Graduate Gemologist or the equivelent thereof so that you know you received the diamond which was advertised... For those of you who are buying a diamond from one of the companies which does not evaluate the diamonds that they represent, this is an absolute MUST because you would shudder to the floor if you knew how many times we have to call our suppliers and tell them that they sent us the wrong diamond... As in "do you still have that other 0.73 carat, E, VS-2 that you offered us? Because the diamond that you sent us matches the lab report for that diamond!" which makes us wonder how many people are wandering around out there with the wrong diamond on their hand?!?! An independent gemologist is likely to catch this oversight and make sure that you actually receive the diamond that you intended to purchase... By the way, we don't think that this is an intentional act by anybody, just an oversight on their part...

6. Veryify the good standing of the company you are purchasing from with the Jewelers Vigilance Committee BEFORE you send money to the company to reduce the chance of becoming a victim - this is for both internet and Brick & Mortar purchases... And make sure that the company offers a full money back satisfaction guarantee so that you may return the diamond for any reason if you are not satisifed... "any reason" does not include damage inflicted to the diamond by you or your jeweler...

Good Luck on your search

 

[Garry H (Cut Nut)]

Robin and Todd wrote ".. we often source diamonds which scored very high on the HCA which we reject for lacking in visual performance and other times keep stones which are exploding with light, but which scored low straight V's on the HCA... And then there are quite a few which score well on the HCA and score well during our selection process... But definitely better than nothing at all for the average consumer! After all, what else do you have to go on? The HCA combined with the Ideal Scope does seem to be a powerful combination....."

Robin and Todd (and others) I would be very happy to have the data on any stones that you believe to be wrongly grade by HCA. As you know I buy and sell too, so my staff are constantly checking the system. I feel the variations we get can always be put down to a specific reason.

I have just submitted an article to Prof Jewler mag that was written about "Girdle Cheating" which is an example of a nasty trick that HCA can not identify. We think a very small % of cutters do this, but we are looking forward to the feedback post publication.

Another article that is under publication review by Rapaport considers diamonds that you would reject because of Cert symmetry comments, are actually perfect stones.

So anyone that sees a stone that has an obviously wrong HCA score - please please give me the data - every case we have been able to learn from, or show that there is a systemic problem (that even AGS and GIA are unaware of).

 

[Garry H (Cut Nut)]

Anothe possible upgrade for HCA is out of roundness.

If a diamond is out of round by 1% and say has a 35 crowen and 41 pavilion - it should get a bigger penalty than say a 34C 40.5P with a 2% out of round.
This would not be hard to do (for a wizz kid like Leonid) and could be just an additional 2 number entry.

Also if we actually had both dimensions and depth, we could pick up girdle cheating and warn consumers (and trade dealers too).

 

[Richard Sherwood]

I ran across one of those "girdle cheating" stones the other day Garry.

It was a 3 ct with a hugely scalloped girdle. At all the points you would measure, it measured medium to slightly thick. In actuality it was extremely thick, with "cheated scallops".

 

[Garry H (Cut Nut)]

So it looked like a 2,5ct stone?

 

[Richard Sherwood]

Yep.

 

[Rhino]

Hi Gary,

R&T will correct me if I'm wrong but they may be referring to 8* type diamonds which score low on the HCA but do not appeal to the eyes of R&T which may boil down to a personal preference issue.

Peace,
Rhino

 

[djgaloot]

NiceIce, others,

Thank you all for your generous information. I am looking forward to purchasing some quality stones but guess I just have a few jitters. I appreciate everyone's input. I'll let you know how it all works out.