GIA EX/EX/EX stone gets low HCA score

[tinv]

Here is the certificate of one of the stones I am considering. Would you let a modeling software that doesn't take into account of many things such as minor facets, digging and painting from buying a stone that GIA has examined in person and assign a Exellence cut rate? It's a small stone and relatively cheap so I am buying from a drop-shipping PS vendors.

Ten years ago when I started looking at diamonds, GIA did not give cut ratings or crown and pavilion angles so everyone was using sarin numbers and HCA result to weed out bad stones. Do we still do that now even with a GIA certificates?

 

[Lorelei]

Here is the certificate of one of the stones I am considering. Would you let a modeling software that doesn't take into account of many things such as minor facets, digging and painting from buying a stone that GIA has examined in person and assign a Exellence cut rate? It's a small stone and relatively cheap so I am buying from a drop-shipping PS vendors.

Ten years ago when I started looking at diamonds, GIA did not give cut ratings or crown and pavilion angles so everyone was using sarin numbers and HCA result to weed out bad stones. Do we still do that now even with a GIA certificates?

Hi Tinv,

With the HCA score, this is a stone I might consider for further evaluation with images as it might be ok depending on some of the factors you mention, especially if the price is right. So no, I wouldn't necessarily let the HCA deter me depending on budget and what I had in mind for the stone. Potential issues I can speculate over could be light leakage due to the angle configuration but looking at some of the other measurements, considering proportion rounding averages and if the overall cut precision was good, these things might help negate any adverse effects such as leakage.

Also the same rules apply as when you and I first started looking at diamonds years ago, especially with the GIA cut grading rounding methods, I would say HCA, consider those scoring <2 and even between 2 and 3 for further evaluation in some cases, then images, then shortlist those for serious purchase consideration. This might be a very nice diamond, from the info we have we can determine it might not be cut to the most exacting levels of precision with the ultimate optical performance in mind, but if the proportions work well together, it could be a very fine stone. But I am speculating, an ASET or Idealscope is needed to tell us more.

Depending on the use you have in mind for the diamond, I would suggest getting an expert to check out this stone to make sure it is eye clean to your specifications, as it's from a drop shipper, see if someone can check this for you should you proceed, also check the location of the feather and if there are any potential durability issues in SI2. Chances are the stone is perfectly fine, but it never hurts to check I believe and I tend to err towards caution anyway.

I would personally want to be able to get some images for this diamond before proceeding to make sure there weren't any negatives or loss of optical performance, but as this is a virtual stone, see if one of the trusted vendors could call it in and do the analysis for you.

I hope this helps a bit. Do you have this diamond in mind for a ring?

 

[Diamond_Hawk]

+1 Lorelei

 

[Todd Gray]

Here is the certificate of one of the stones I am considering. Would you let a modeling software that doesn't take into account of many things such as minor facets, digging and painting from buying a stone that GIA has examined in person and assign a Exellence cut rate? It's a small stone and relatively cheap so I am buying from a drop-shipping PS vendors.

Ten years ago when I started looking at diamonds, GIA did not give cut ratings or crown and pavilion angles so everyone was using sarin numbers and HCA result to weed out bad stones. Do we still do that now even with a GIA certificates?

As you've indicated, the intent behind the HCA is to help consumers weed out diamonds which are likely to exhibit lesser degrees of light return and visual performance, and I think it remains useful for that purpose. However I think that people would be well served by running diamonds through the program twice, once using the crown and pavilion angle measurements, and once more using the crown height and pavilion depth measurements, to get a more accurate impression of the diamond since the two are not necessarily in sync with one another.

In addition, remember that the GIA and the AGS measure lower girdle length differently, the GIA measures lower girdle length by radius, while the AGS measures it by length, thus if you're attempting to "buy a diamond by the numbers" it is important to realize that the numbers add up differently depending on which gemological laboratory graded the diamond... hence the importance of reflector scope images.

 

[Lorelei]

Hey Todd, it's good to see you!

 

[WinkHPD]

Here is the certificate of one of the stones I am considering. Would you let a modeling software that doesn't take into account of many things such as minor facets, digging and painting from buying a stone that GIA has examined in person and assign a Exellence cut rate? It's a small stone and relatively cheap so I am buying from a drop-shipping PS vendors.

Ten years ago when I started looking at diamonds, GIA did not give cut ratings or crown and pavilion angles so everyone was using sarin numbers and HCA result to weed out bad stones. Do we still do that now even with a GIA certificates?

ABSOLUTELY!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

GIA grading reports are pretty much worthless as far as cut grading goes. Their numbers are too rounded to depend on and they reward too many diamonds that are not of top visual quality with their excellent ranking.

Now that so many cutters have figured out how to "job" the system by cutting to the outer limits of a GIA X the market is flooded with stones that are nothing more than pretenders. This makes it even more important to "run the numbers" and to see reflector images, not less.

Wink

 

[Todd Gray]

Here is the certificate of one of the stones I am considering. Would you let a modeling software that doesn't take into account of many things such as minor facets, digging and painting from buying a stone that GIA has examined in person and assign a Exellence cut rate? It's a small stone and relatively cheap so I am buying from a drop-shipping PS vendors.

Ten years ago when I started looking at diamonds, GIA did not give cut ratings or crown and pavilion angles so everyone was using sarin numbers and HCA result to weed out bad stones. Do we still do that now even with a GIA certificates?

ABSOLUTELY!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

GIA grading reports are pretty much worthless as far as cut grading goes. Their numbers are too rounded to depend on and they reward too many diamonds that are not of top visual quality with their excellent ranking.

Now that so many cutters have figured out how to "job" the system by cutting to the outer limits of a GIA X the market is flooded with stones that are nothing more than pretenders. This makes it even more important to "run the numbers" and to see reflector images, not less.

Wink

Why don't you share with the group how you really feel Mr. Jones?

I mean like, you know that I was thinking it... but you actually SAID IT... Like "Out Loud"

Even though I can already picture this diamond in my head, I clicked over to the HCA to run the numbers using both the angles and percentages and it gets 4.1 Good if you go by the angles, and 3.3 Very Good if you go with the percentages... all of which of course is based upon the averages. For the sake of newbie's who might trip across this thread, the reason why it's important to consider both the angle and depth percentages is because the upper and lower sections of the diamond need to be "balanced" in order for light to travel through the diamond properly, the ratio is generally one third for the crown (top) section and two thirds for the pavilion (lower) section, with minor adjustments required for the girdle edge.

In this particular instance, the reason the HCA is downgrading the diamond is most likely because it considers the crown angle to be too steep at 36 degrees and this is affecting the total depth of the diamond. However when the HCA considers the diamond based upon the depth measurements, it concludes that the balance between the sections of the diamond are correct, but in reality the sections are correct, but the cutter figured out how to increase the carat weight of the diamond by pushing the crown angle out further by extending the table diameter...

Is this good or bad? That my friends depends on your personal preference for the way you want your diamond to look, some people prefer smaller table facets, other people prefer larger table facets, and different combinations of crown / pavilion angle, and even the depth percentages will provide different levels of visual performance.

Clearly this diamond is exactly what tinv is looking for, and it appears that tinv has the experience to understand how the factors of diamond cut quality interact with each other to produce a desired effect, I'm being long winded and providing a more in-depth answer because a lot of the people who trip across this thread might not be as familiar with the differences between the GIA Excellent / AGS Ideal cut grades, and how the labs differ in how they determine the proportions grades.

Good to see you also Lorelei

 

[Lorelei]

Here is the certificate of one of the stones I am considering. Would you let a modeling software that doesn't take into account of many things such as minor facets, digging and painting from buying a stone that GIA has examined in person and assign a Exellence cut rate? It's a small stone and relatively cheap so I am buying from a drop-shipping PS vendors.

Ten years ago when I started looking at diamonds, GIA did not give cut ratings or crown and pavilion angles so everyone was using sarin numbers and HCA result to weed out bad stones. Do we still do that now even with a GIA certificates?

ABSOLUTELY!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

GIA grading reports are pretty much worthless as far as cut grading goes. Their numbers are too rounded to depend on and they reward too many diamonds that are not of top visual quality with their excellent ranking.

Now that so many cutters have figured out how to "job" the system by cutting to the outer limits of a GIA X the market is flooded with stones that are nothing more than pretenders. This makes it even more important to "run the numbers" and to see reflector images, not less.

Wink

Why don't you share with the group how you really feel Mr. Jones?

I mean like, you know that I was thinking it... but you actually SAID IT... Like "Out Loud"


Good to see you also Lorelei

Hahaha! Wink even used red ink to make his point.....

 

[JulieN]

This combo needs to be looked at. It might show leakage under IS but could be fine irl.