AGS light performance grade 0 with HCA < 1

[insured]

I have read all the discussion I can find on HCA scores < 1 and understand well that they can be nice performers or can be subject to excessive obstruction to direct light return at close range, and much depends on symmetry. Some places it's been suggested that an AGS 0 grade negates any concern of this possibility in a stone scoring under 1 on HCA.

Seeking opinions on whether an AGS 000 with light performance score 0 weeds out the stones with HCA < 1 that would be subject to excessive darkening at close range.

As always, thanks to anyone willing to weigh in!

 

[Texas Leaguer]

An AGS 0 light performance based certificate provides a lot more information than the HCA. It is based on ray tracing the actual 3D model of the diamond and takes into account the effects of each individual facet (as opposed to an averaged measurement of a few). Contrast is a central part of the AGS analysis and is based upon a viewing distance of 9.84 in, the standard in the field of optometry as the distance of most distinct vision for a person with normal vision.

 

[insured]

An AGS 0 light performance based certificate provides a lot more information than the HCA. It is based on ray tracing the actual 3D model of the diamond and takes into account the effects of each individual facet (as opposed to an averaged measurement of a few). Contrast is a central part of the AGS analysis and is based upon a viewing distance of 9.84 in, the standard in the field of optometry as the distance of most distinct vision for a person with normal vision.

THanks for the reply. I understand that the AGS light performance gives more info than the HCA - still not sure though if a 0 score rules out a less than pleasant looking amount of head obstruction. Such a stone for example could have lots of contrast but up to 50% of the stone is black, no?

I have seen it stated (possibly by the same poster) in several places that if you have an AGS light performance 0, HCA doesn't add anything. Is there a general degree of consensus on this or just one person's oversimplified take?

Thanks.

 

[Texas Leaguer]

I am not the arbiter of general consensus here but I think most people understand that HCA is a great tool for filtering stones for consideration from lists of diamonds where only basic information is available. It was particularly useful in the time before AGS developed their light performance based cut grading system. The sophistication of that system makes an HCA score moot in the presence of a Triple Zero report.

You can read the science behind the system here.
http://www.agslab.com/spie/spie_lo_res.pdf

It is interesting to note the chief scientist of the system’s development is a professor of optical engineering and astronomy who designs mirror systems for major ground based telescopes. Since a diamond is a system of tiny mirrors it makes a lot of sense!

 

[insured]

I am not the arbiter of general consensus here but I think most people understand that HCA is a great tool for filtering stones for consideration from lists of diamonds where only basic information is available. It was particularly useful in the time before AGS developed their light performance based cut grading system. The sophistication of that system makes an HCA score moot in the presence of a Triple Zero report.

You can read the science behind the system here.
http://www.agslab.com/spie/spie_lo_res.pdf

It is interesting to note the chief scientist of the system’s development is a professor of optical engineering and astronomy who designs mirror systems for major ground based telescopes. Since a diamond is a system of tiny mirrors it makes a lot of sense!

Thanks again for the input and article. I take the gist of the bolded sentence above to mean that you DO believe an AGS triple zero negates any POTENTIAL concerns of excessive darkening due to head shadow with HCA score below 1. Is that correct? Forgive me for being dense!

 

[Paul-Antwerp]

The consensus-rule about HCA-scores under 1 developed gradually on PS, and is about as useful as the advice to young men to avoid dating a super-pretty girl.

If a diamond with HCA-score under 1 is cut correctly, it is more likely to be a super-performer than one with a score between 1 and 2, in my opinion.

However, if it is cut a bit sloppily, the negative effect of that sloppiness will be quickly noticeable, whereas a diamond scoring between 1 and 2 has some more room for sloppiness.

My advice is to discard that consensus-rule, and to use the HCA as the rejection-tool it was designed to be.

Live long

 

[Texas Leaguer]

I am not the arbiter of general consensus here but I think most people understand that HCA is a great tool for filtering stones for consideration from lists of diamonds where only basic information is available. It was particularly useful in the time before AGS developed their light performance based cut grading system. The sophistication of that system makes an HCA score moot in the presence of a Triple Zero report.

You can read the science behind the system here.
http://www.agslab.com/spie/spie_lo_res.pdf

It is interesting to note the chief scientist of the system’s development is a professor of optical engineering and astronomy who designs mirror systems for major ground based telescopes. Since a diamond is a system of tiny mirrors it makes a lot of sense!

Thanks again for the input and article. I take the gist of the bolded sentence above to mean that you DO believe an AGS triple zero negates any POTENTIAL concerns of excessive darkening due to head shadow with HCA score below 1. Is that correct? Forgive me for being dense!

In my opinion you should not be concerned about contrast in a Triple Zero. It will not have too much or too little. It is one of the fundamental factors of light performance that is evaluated by the AGS LP system. It is essential to have enough contrast to create scintillation.

As Paul suggests, the precision of the cutting is something a score alone will not tell you. That is why prosumers here like to see Ideal Scope, ASET and H&A pics to make more refined judgments.

AGS also has a tool called the VPA that helps evaluate faceting precision.

 

[insured]

The consensus-rule about HCA-scores under 1 developed gradually on PS, and is about as useful as the advice to young men to avoid dating a super-pretty girl.

If a diamond with HCA-score under 1 is cut correctly, it is more likely to be a super-performer than one with a score between 1 and 2, in my opinion.

However, if it is cut a bit sloppily, the negative effect of that sloppiness will be quickly noticeable, whereas a diamond scoring between 1 and 2 has some more room for sloppiness.

My advice is to discard that consensus-rule, and to use the HCA as the rejection-tool it was designed to be.

Live long

LOL Paul! Hot men are best avoided too

Re: sloppy cutting - I've noted your valued opinion previously that a perfectly cut diamond close to the edge is indeed the bees knees. Interesting that this seems to conflict with Gary Holloway's statement that "Stones near the center of the red region, those with the lowest scores, are often the least affected by small symmetry variations."

If I may ask your specific opinion on the following ASET - certainly less than perfect optical symmetry, HCA 0.7. Your thoughts where this one might fall on the sloppy/sweet spectrum? http://www.agslab.com/pdf_sync_reports/104055025045-PLDQR.PDF

Thanks for your input

 

[insured]

In my opinion you should not be concerned about contrast in a Triple Zero. It will not have too much or too little. It is one of the fundamental factors of light performance that is evaluated by the AGS LP system. It is essential to have enough contrast to create scintillation.

As Paul suggests, the precision of the cutting is something a score alone will not tell you. That is why prosumers here like to see Ideal Scope, ASET and H&A pics to make more refined judgments.

AGS also has a tool called the VPA that helps evaluate faceting precision.

Thanks once again TL. Your thoughts on the above ASET posted above would also be appreciated, specifically on if the optical symmetry is off enough to worry about a reduction in performance wrt light return at close viewing and with tilt. It's not really a loss of contrast I'm worried about, I know the stone has a ton of it.

 

[Texas Leaguer]

In my opinion you should not be concerned about contrast in a Triple Zero. It will not have too much or too little. It is one of the fundamental factors of light performance that is evaluated by the AGS LP system. It is essential to have enough contrast to create scintillation.

As Paul suggests, the precision of the cutting is something a score alone will not tell you. That is why prosumers here like to see Ideal Scope, ASET and H&A pics to make more refined judgments.

AGS also has a tool called the VPA that helps evaluate faceting precision.

Thanks once again TL. Your thoughts on the above ASET posted above would also be appreciated, specifically on if the optical symmetry is off enough to worry about a reduction in performance wrt light return at close viewing and with tilt. It's not really a loss of contrast I'm worried about, I know the stone has a ton of it.

I would defer to Paul to answer your specific question. I would make this general statement that you may find helpful. The stone you reference will be very bright and beautiful although not a perfect hearts and arrows diamond. It's got a very powerful engine. The precision of the cut in 3 dimensions is like the tuning of that engine. Could this one be tuned up a little. Yes. Will you notice the deficit in real life. Probably not.

 

[insured]

I would defer to Paul to answer your specific question. I would make this general statement that you may find helpful. The stone you reference will be very bright and beautiful although not a perfect hearts and arrows diamond. It's got a very powerful engine. The precision of the cut in 3 dimensions is like the tuning of that engine. Could this one be tuned up a little. Yes. Will you notice the deficit in real life. Probably not.

Thanks TL, I appreciate your input. Insurance replacement constraints are keeping me from freedom of choice, and just trying to find a level of comfort with the reservations I have about this stone. It did seem dark to me in person and I'm just trying to convince myself that it really will be okay. I want to believe I'm imagining it but knowing that some stones with HCA < 1 CAN be dark makes me fear I'm right.

To Yssie, who has been most generous with her help previously: the Lazare was my first choice but the jeweller pulled a bait and switch on me with the setting which would have required significant cash infusion over my insurance reimbursement (and continuing to do business with him after his dirty tricks, grrrr!). Hence the 'dark' corner I now find myself in

 

[Texas Leaguer]

I would defer to Paul to answer your specific question. I would make this general statement that you may find helpful. The stone you reference will be very bright and beautiful although not a perfect hearts and arrows diamond. It's got a very powerful engine. The precision of the cut in 3 dimensions is like the tuning of that engine. Could this one be tuned up a little. Yes. Will you notice the deficit in real life. Probably not.

Thanks TL, I appreciate your input. Insurance replacement constraints are keeping me from freedom of choice, and just trying to find a level of comfort with the reservations I have about this stone. It did seem dark to me in person and I'm just trying to convince myself that it really will be okay. I want to believe I'm imagining it but knowing that some stones with HCA < 1 CAN be dark makes me fear I'm right.

Be mindful of the lighting in the store or office where you are viewing the diamond. Make sure you can make an assessment in a lighting environment with diffuse full spectrum fluorescent light. Many stores are equipped with LED lighting these days. They do some beautiful things for diamonds but can also accentuate contrast.

 

[insured]

Be mindful of the lighting in the store or office where you are viewing the diamond. Make sure you can make an assessment in a lighting environment with diffuse full spectrum fluorescent light. Many stores are equipped with LED lighting these days. They do some beautiful things for diamonds but can also accentuate contrast.

This particular jeweller actually makes a point of pride of avoiding LED lights, and makes sure you know it and keep it in mind when comparing to things you see at other jewellers, although he does have halogen track lights. There are large full windows across the front of the store for daylight viewing. It was in daylight viewing and with tilt that the diamond looked concerningly dark to me and I suspect a good part of it is very generous head shadow. More so than my previous stone being replaced, which was also AGS 000 with visible arrows, although it predated the AGS light performance reports.

 

[Paul-Antwerp]

The consensus-rule about HCA-scores under 1 developed gradually on PS, and is about as useful as the advice to young men to avoid dating a super-pretty girl.

If a diamond with HCA-score under 1 is cut correctly, it is more likely to be a super-performer than one with a score between 1 and 2, in my opinion.

However, if it is cut a bit sloppily, the negative effect of that sloppiness will be quickly noticeable, whereas a diamond scoring between 1 and 2 has some more room for sloppiness.

My advice is to discard that consensus-rule, and to use the HCA as the rejection-tool it was designed to be.

Live long

LOL Paul! Hot men are best avoided too

Re: sloppy cutting - I've noted your valued opinion previously that a perfectly cut diamond close to the edge is indeed the bees knees. Interesting that this seems to conflict with Gary Holloway's statement that "Stones near the center of the red region, those with the lowest scores, are often the least affected by small symmetry variations."

If I may ask your specific opinion on the following ASET - certainly less than perfect optical symmetry, HCA 0.7. Your thoughts where this one might fall on the sloppy/sweet spectrum? http://www.agslab.com/pdf_sync_reports/104055025045-PLDQR.PDF

Thanks for your input

Hello Insured,

I have my reservations about online-assessment of diamonds, regarding all potential tools as rejection-tools at best and personal confirmation and preferably choice necessary to truly assess diamonds. However, given your situation, I will do my best to give you my opinion, with some reservation.

- On the basis of the available info, I see no direct reason for this diamond to seem dark. I would at least expect it to be a bright stone, essentially the same position as TL.
- The printed ASET indicates the stone not being cut to the best cut-precision, but I would advise confirming that live in an actual ASET-scope. I have seen and experienced other examples of AGSL making mistakes in their ASET-print. The stone could be better than that ASET indicates.
- However, I see no indication for the stone to appear dark in real life. I would suggest to re-examine the diamond in real life in various light-environments. You will have to wear it, and if you feel that despite the paperwork and the quick online-assessment, the stone does not perform in the way you want, then you need to pass. None of us can make this decision for you, I think.

Do understand however the position of your jeweler too. As a cutter, I know very well how difficult it is to produce perfectly cut diamonds to AGS-standards or better in such somewhat smaller sizes, and end up with a final price that can be defended. The extra loss of weight and the fixed expenses attached have a much higher impact in smaller diamonds, and as a result, it is kind of natural to find only limited number of such quality diamonds available.

In that sense, your jeweler probably has done a great job in finding you this stone, and if this does not work, you will need to give him time to find a better one. From what you have posted about them, it seems to be a high-quality-outfit, all the more reason to understand that they simply cannot pick such diamonds off the shelf.

Live long,

 

[Texas Leaguer]

Be mindful of the lighting in the store or office where you are viewing the diamond. Make sure you can make an assessment in a lighting environment with diffuse full spectrum fluorescent light. Many stores are equipped with LED lighting these days. They do some beautiful things for diamonds but can also accentuate contrast.

This particular jeweller actually makes a point of pride of avoiding LED lights, and makes sure you know it and keep it in mind when comparing to things you see at other jewellers, although he does have halogen track lights. There are large full windows across the front of the store for daylight viewing. It was in daylight viewing and with tilt that the diamond looked concerningly dark to me and I suspect a good part of it is very generous head shadow. More so than my previous stone being replaced, which was also AGS 000 with visible arrows, although it predated the AGS light performance reports.

I recommend viewing in a controlled full spectrum diffused lighting environment. People often assume that a window gives you those conditions but the light tends to be directional and most buildings have a tinting on the glass for energy conservation that alters the nature of the light significantly.

Following on what Paul said about the ASET on the report, it is a computer generated light map. If you are concerned about the patterning/contrast it would be good to have your vendor provide you an actual ASET image for comparison.

 

[insured]

Hello Insured,

I have my reservations about online-assessment of diamonds, regarding all potential tools as rejection-tools at best and personal confirmation and preferably choice necessary to truly assess diamonds. However, given your situation, I will do my best to give you my opinion, with some reservation.

- On the basis of the available info, I see no direct reason for this diamond to seem dark. I would at least expect it to be a bright stone, essentially the same position as TL.
- The printed ASET indicates the stone not being cut to the best cut-precision, but I would advise confirming that live in an actual ASET-scope. I have seen and experienced other examples of AGSL making mistakes in their ASET-print. The stone could be better than that ASET indicates.
- However, I see no indication for the stone to appear dark in real life. I would suggest to re-examine the diamond in real life in various light-environments. You will have to wear it, and if you feel that despite the paperwork and the quick online-assessment, the stone does not perform in the way you want, then you need to pass. None of us can make this decision for you, I think.

Do understand however the position of your jeweler too. As a cutter, I know very well how difficult it is to produce perfectly cut diamonds to AGS-standards or better in such somewhat smaller sizes, and end up with a final price that can be defended. The extra loss of weight and the fixed expenses attached have a much higher impact in smaller diamonds, and as a result, it is kind of natural to find only limited number of such quality diamonds available.

In that sense, your jeweler probably has done a great job in finding you this stone, and if this does not work, you will need to give him time to find a better one. From what you have posted about them, it seems to be a high-quality-outfit, all the more reason to understand that they simply cannot pick such diamonds off the shelf.

Live long,

Thanks so much Paul. I understand your reservations on weighing in, and appreciate the extent of your input. It helps very much to have the opinion of someone in your position to correlate the degree of imprecision with the degree of anticipated effect, and that no one's got the crystal ball to replace looking into the diamond.

Unfortunately scopes of any kind haven't made it to my relatively small corner of the world to use in person yet, but I had already thought perhaps the printed ASET might be sloppier than the cutting. One can hope.

In no way do I think poorly of this jeweller for this stone. I know he did work hard to find it and takes pains to accurately represent his goods. The other branded dealer who pulled a bait and switch on me is another story... Nice stones but I refuse to reward his sales methods!

Once again, thanks.

 

[insured]

I recommend viewing in a controlled full spectrum diffused lighting environment. People often assume that a window gives you those conditions but the light tends to be directional and most buildings have a tinting on the glass for energy conservation that alters the nature of the light significantly.

Following on what Paul said about the ASET on the report, it is a computer generated light map. If you are concerned about the patterning/contrast it would be good to have your vendor provide you an actual ASET image for comparison.

We did look under a full spectrum large area diamond grading light and in the doorway without coated glass, but thanks for the additional viewing tips. No overhead fluorescent lighting but maybe there is some in the back. Thanks for your input, and here's hoping it's all in my head!