Fish Eye? Why buying by the #''s doesn''t always work...

[niceice]

With all due respect to Garry and the work that he is doing with the HCA we want to share an example of why "buying by the numbers" using HCA results as the basis for making a decision does not always work and why it is important to base your decision to purchase or not purchase a diamond based upon an actual evaluation of the diamond by an experienced diamond grader... We also want to point out, that there is a paragraph to this effect that appears on the HCA page just below the results section... Understand that this is NOT an attack upon the HCA - simply an example of why the results should only be considered as a possible indicator and not a definite indicator of what a diamond might look like...

In this particular instance, we brought a non-ideal cut diamond in for evaluation on behalf of a customer who was looking for a nice "bluff stone" - a non-ideal cut diamond that exhibits similar light return to an ideal cut diamond... The diamond is GIA #13371869 and it measures 6.17 x 6.21 x 3.79 mm with a total depth of 61.2% with a 60% table diameter and a crown angle of 35.5 degrees with a pavilion angle of 39.9 degrees with a slightly thick to thick girdle. It scored as follows on the HCA:

We want to draw your attention to the notation under the results which claims that "a small amount of tilt will show a fish-eye under the table of this diamond." which is an unfortunate assumption that is being made "by the numbers" when in fact, this diamond exhibits no such characteristic... If the diamond were evaluated for purchase by the results of the HCA alone, it might be passed over for a comment such as this which would be unfortunate because the diamond is truly beautiful and is right up there in terms of the actual degree of light return. Here are pictures of the diamond as seen through our Gem Scope "straight on" and at a slight tilt.

No fish-eye to be found

The only way to "buy your diamond buy the numbers" with any degree of accuracy is to do so with the assistance of an experienced diamond grader... Realize that programs like the HCA evaluate diamonds based on mathematical averages which will not always represent a diamond accurately because while a lot can be derived regarding a diamonds potential "by the numbers" the decision to purchase a diamond still requires a trained set of eye balls

 

[researcher]

Wow! Thanks for sharing. I'm someone who believes numbers can help people to narrow down their choices, but I guess people should still look into stones that they feel could really be right for them because of price or whatever! Very interesting

 

[strmrdr]

Can you post a couple pictures under the same lighting conditions/scope of a near h&a stone (by your definition :} aka h&a diamond to most every other dealer )?

That will give a frame of reference for people to compare too.

My problem with the hca is that it doesn’t seem to take enough things into account to truly tell what a diamond is going to look like.
Maybe it might be right for say 80% (picked a number out of the air) of the diamonds cut like that one but its possibly wrong for some because of other factors in the cut that it doesn’t take into account.

The more I study diamonds the less I know about them and you know what it seems like the "experts" are finding out the same thing about themselves wether they will admit it or not :}

Nothing personal to any individual just a general observation on this line of study that seems to be in its infancy.

 

[oldminer]

Garry can surely do his own answering, but it would look to me like the stone faces-up very nicely. However, if one takes such a diamond and tilts it a bit, the 'fish-ey" may be more apparent than in a more standard sort of near ideally cut diamond. That does not mean it is a bad diamond for a budget situation or that no one would ever like it. To me the warning with the HCA may be called for and then the customer just makes up their own mind how to compromise. No doubt, the stone was not D-IF, so a compromise was being made in many instances here.

Numbers doa good job of sorting out bad or dangerous stones. They do not serve to identify every great looking one or every poor one, but used judiciously, numbers assist more than create problems. A few diamonds with somewhat off numbers may do well, but they are not the industry standard. They are a decent compromise for someone sticking to a budget game plan.

 

[aljdewey]

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With all due respect to Garry and the work that he is doing with the HCA we want to share an example of why 'buying by the numbers' using HCA results as the basis for making a decision does not always work and why it is important to base your decision to purchase or not purchase a diamond based upon an actual evaluation of the diamond by an experienced diamond grader. We also want to point out, that there is a paragraph to this effect that appears on the HCA page just below the results section. Understand that this is NOT an attack upon the HCA - simply an example of why the results should only be considered as a possible indicator and not a definite indicator of what a diamond might look like...----------------

R/T, I know you mean well, but it seems to me you're trying to sell those who are already sold.

"The numbers" have been discussed ad naseum over the last several months, and the general consensus/message repeated here is "numbers only help narrow the field...they aren't a replacement for an independent evaluation."

I can't think of anyone here who has advised someone to buy sheerly by the numbers without having a trained professional look at the stone.

Why keep trying to convert the already converted?

(Or have I missed something on this front that prompted another repetition of the message?)

On 6/16/2004 4:05:07 PM niceice wrote:

If the diamond were evaluated for purchase by the results of the HCA alone....

But no one has said a diamond should be purchased by the HCA alone....so this is kind of a moot point.

 

[purduephotog]

I think the term is 'mono-numerosis'. It's a rare condition contracted by most forms of management. The disease is progressive- the higher the food chain, the longer the disease has incubated, the greater reduction in brain power.

It's a very sad condition to have to witness. In extreme cases (such as CEO's) simply stating things such as "The test scores 4.5 vs the competitors 1.8" can cause grins and celebration as well as immediate notification of the PR department to send out notes.

The only cure is repeated failing; unfortunately that just causes the CEO (in my example) to move to another host and begin the infection processes again.


In all seriousness, that's a very good post- I had seen a stone that warned of 'fisheye' and actually had listed a fisheye region. Not having the stone in hand (and not finding vendors willing to photograph them cheaply ) I took it on as 'not worth the risk'.

Thank you for the education; I'm still goign to be hesitant... but not so much.

Just for personal edification, how 'slight' was this tilt? Did a 10 degree tilt show a fisheye?

 

[aljdewey]

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On 6/16/2004 4:50:27 PM purduephotog wrote:




In all seriousness, that's a very good post- I had seen a stone that warned of 'fisheye' and actually had listed a fisheye region. Not having the stone in hand (and not finding vendors willing to photograph them cheaply ) I took it on as 'not worth the risk'.

Thank you for the education; I'm still goign to be hesitant... but not so much.----------------

It all depends on someone's definition of risk.

If my only risk as a consumer was that I would see such a stone at my local jewelers and not like it, then I'd be a bit more receptive to considering potential peripheral stones.

If, however, I had to pay $70 in round-trip shipping charges for each diamond I wanted to see (or have my appraiser evaluate), I'd probably be less likely to gamble IF there are more potentially promising stones available.

 

[niceice]

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On 6/16/2004 4:31:08 PM aljdewey wrote:

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R/T, I know you mean well, but it seems to me you're trying to sell those who are already sold. The numbers' have been discussed ad naseum over the last several months, and the general consensus/message repeated here is 'numbers only help narrow the field...they aren't a replacement for an independent evaluation.'----------------

It is true that the concept has been discussed repeatedly over the years here on PS, but the reality is that there are new people here on PS every day and thus we felt the topic pertaining to a specific example and not just a concept of averages was worthy of exploration...

Regarding the question pertaining to whether a fish-eye was visible at 10 degrees, etc. No, a fish eye was not visible in the stone at any angle... We posted the one photograph because it faced up the best in terms of showing a depth of field within the table facet... We'll post a photograph of an H&A type stone at a similar tilt a little later today when we sit down to photograph the parcel of diamonds that arrived this afternoon...

 

[niceice]

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On 6/16/2004 4:20:31 PM oldminer wrote:

To me the warning with the HCA may be called for and then the customer just makes up their own mind how to compromise.----------------

Perhaps it would be better if the warning used the word "may" instead of "will" in referring to the possiblity that it could exhibit a fish-eye. Thus the interpretation of the numbers would be a possible indication instead of being an absolute statement.

 

[niceice]

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On 6/16/2004 4:17:09 PM strmrdr wrote:

Can you post a couple pictures under the same lighting conditions/scope of a near h&a stone (by your definition :} aka h&a diamond to most every other dealer )?

That will give a frame of reference for people to compare too.----------------

This is a picture of a 1.36 carat, G, IF that we are in the process of checking in as seen at a similar tilt:

 

[Mara]

Buying solely by HCA does not work...but buying solely by eye in my opinion doesn't work either. Middle ground...

If you have a trustworthy vendor, such as R/T or similar who can eyeball a stone for you and you can trust their opinion...then you will be able to explore more options than you would if you were doing it all on your own. If you are buying solely through your own research, online using specs, reports, numbers, images...that is where the HCA comes in handy along with other data, to assist in weeding out 'possible chaff'.

 

[hoorray]

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On 6/16/2004 6:13:43 PM Mara wrote:


Buying solely by HCA does not work...but buying solely by eye in my opinion doesn't work either. Middle ground...

If you have a trustworthy vendor, such as R/T or similar who can eyeball a stone for you and you can trust their opinion...then you will be able to explore more options than you would if you were doing it all on your own. If you are buying solely through your own research, online using specs, reports, numbers, images...that is where the HCA comes in handy along with other data, to assist in weeding out 'possible chaff'.
----------------

I think we forget that many e-ring buyers do not have trusted relationships with a jeweler yet - online or off. Once they buy their stone and ring, they hopefully will have developed one, but in the just getting started phase, it's a big leap of faith to put complete trust in someone you have not done business with before, have never met, and are expected to wire thousands of $$ to. Thus, tools such as the HCA, and the numbers in general give you a way to help validate whether what a vendor is telling you makes sense or not. At least at a high level. Half the work of buying from an online vendor is getting comfortable with the process and a vendor.

 

[niceice]

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On 6/16/2004 7:19:40 PM lop wrote:

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Thus, tools such as the HCA, and the numbers in general give you a way to help validate whether what a vendor is telling you makes sense or not. At least at a high level. Half the work of buying from an online vendor is getting comfortable with the process and a vendor.----------------

Again, we want to be CLEAR that we are NOT trying to say that the HCA is not a valuable evaluation tool, merely that it is only part of the puzzle and not an absolute indicator of a stone's potential... Use it to narrow down the options and then ask a professional to assist you with the selection process from there. There are "many" trusted and established vendors here on PS who can assist you with the process of buying a diamond on-line successfully.

 

[aljdewey]

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On 6/16/2004 7:31:35 PM niceice wrote:

Again, we want to be CLEAR that we are NOT trying to say that the HCA is not a valuable evaluation tool, merely that it is only part of the puzzle and not an absolute indicator of a stone's potential.
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.....And for the benefit of those "new folks" R/T referred to who may not know otherwise, the HCA never claimed to be an absolute indicator of a stone's potential. That's not why it was developed, nor does it claim to "select" the best stones.

It is touted as a way to help weed out poor performers. It's not a selection tool, it's an elimination tool.....a tool to help narrow down the field of possible candidates. That's all.

 

[strmrdr]

Thanks niceice for the comparison shot.
It makes it easier to understand what your comparing it too :}

 

[niceice]

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On 6/16/2004 8:47:15 PM aljdewey wrote:

----------------...And for the benefit of those 'new folks' R/T referred to who may not know otherwise, the HCA never claimed to be an absolute indicator of a stone's potential. That's not why it was developed, nor does it claim to 'select' the best stones.

It is touted as a way to help weed out poor performers. It's not a selection tool, it's an elimination tool.....a tool to help narrow down the field of possible candidates. That's all

----------------/blockquote>

EXACTLY! Unfortunately too many people misinterpret the HCA to be an "absolute" indicator of brilliance, dispersion and scintillation and get all to caught up in the results... We know because we hear about it all day long and the funny thing is that our diamonds tend to score quite nicely on the HCA... But people will ask "Which of the diamonds should I buy? The one that scored 1.7 on the HCA or the one that scored 1.5?" and the reality is that both are probably phenomenal stones... We do object however to the statement that the proportions "will" exhibit a fish eye as opposed to the fact that it should probably say "may" or "might" because such language contributes to the mis-interpretation of the tools intentions...

 

[Garry H (Cut Nut)]

Sorry guys - that stone has a fish eye when titled.
You can see the little spots on the left.
It is physics - you guys are into engineering - you should know that.

 

[Garry H (Cut Nut)]

All diamond show the girdle through the table when titled - so all diamonds show a fish eye.

Put some bright colored ink or paint on the girdle and you will see it.

To see the fish eye all around then you need no tilt.
If the girdle is faceted and the stone is prong set then the gridle can act as a seperate set of facets - like the case of the 4 big girdle facets on the Regent.

 

[niceice]

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On 6/17/2004 11:37:08 AM Garry H (Cut Nut) wrote:

Sorry guys - that stone has a fish eye when titled.
You can see the little spots on the left.----------------

Sorry Garry, but we really didn't see the fish eye and we were staring at the stone for quite some time trying to find the effect because we would have loved to capture a really good photograph of a fish-eye to use as an example of such on our web site... We ended up rejecting the diamond by the way based upon how messy it looked internally because of the mirroring of the primary inclusions being so substantial which might be what you're seeing as little spots along the left, but we didn't reject it for having a fish eye.

 

[scotch]

Robin & Todd,

by how much have you tilted the diamond? I tried simulating the stone with DiamCalc, and when tilted by 15 degrees, the (simulated) picture shows a definite fisheye effect (see picture). Btw, the DiamCalc cut evaluation gives it a definite hit in the fisheye score, it comes out 0.75 [good]. So it's not an extreme effect, but you would expect to find it. Of course, this is only a simulation.

Scotch

 

[niceice]

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On 6/17/2004 12:50:30 PM scotch wrote:

Robin & Todd, by how much have you tilted the diamond? I tried simulating the stone with DiamCalc, and when tilted by 15 degrees, the (simulated) picture shows a definite fisheye effect (see picture). Btw, the DiamCalc cut evaluation gives it a definite hit in the fisheye score, it comes out 0.75 [good]. So it's not an extreme effect, but you would expect to find it. Of course, this is only a simulation.----------------

We understand that "mathematically" it is "possible" for a diamond with these measurements to exhibit a fish eye. The point is that this doesn't mean that it "will" exhibit a fish eye... Everybody who knows us recognizes that we're big fans of number crunching to narrow down the possibilities when it comes to diamond selection, but from time to time the anticipated results do not equal the reality of a specific stone. The same holds true for a diamond cut like a dream from a numerical perspective, sometimes it simply fails to produce the desired visual effect.

The specific degree of tilt? We didn't measure it, we just held the diamond in a pair of tweezers and rolled it about looking for the fish eye effect simply because the HCA indicated that the diamond had one and we thought it would be cool to capture it... So we're actually disappointed that it doesn't exhibit a distinct fish eye effect that can be captured for use on our site... Again, all we're saying is use the HCA, DiamCalc, etc. to narrow down the field, but then it's time to use your eyes...

 

[scotch]

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We understand that 'mathematically' it is 'possible' for a diamond with these measurements to exhibit a fish eye. The point is that this doesn't mean that it 'will' exhibit a fish eye...
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Can't help it, I just have to try and figure out why reality doesn't do what it's supposed to...

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Everybody who knows us recognizes that we're big fans of number crunching to narrow down the possibilities when it comes to diamond selection, ...----------------

I know, just love your website!

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Again, all we're saying is use the HCA, DiamCalc, etc. to narrow down the field, but then it's time to use your eyes...
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Couldn't agree more. Greetings,
Scotch

 

[Garry H (Cut Nut)]

R&T if you still have that stone then please try this experiment:

Set it in a rubbed in Yellow gold bezel with a little grease on the girdle to show what the stone will look like in a few months time. Then tell us what you think of the fish eye

 

[niceice]

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On 6/17/2004 4:56:24 PM Garry H (Cut Nut) wrote:

R&T if you still have that stone then please try this experiment:

Set it in a rubbed in Yellow gold bezel with a little grease on the girdle to show what the stone will look like in a few months time. Then tell us what you think of the fish eye

----------------

We rejected the stone and sent it back, but what you're saying is that the fish eye that we don't see, would be more apparent if the stone were set? Interesting... We don't see many stones cut like this as you might imagine, so they're kind of a curiosity for us...