Great HCA Score but Outside of ''Ideal'' Zones - what does this mean?

[Jeanne61]

Hi, I ran across a stone with the HCA scores below. As you can see, the scores 4 Excellents with an overall .7 in the TIC range, yet it still falls outside of the GIA and AGS ideal ranges -what does this mean? What kind of light performance will this stone likely give?

BTW - this is a J, SI stone with Excellent Symmetry and Polish and Med Blue Fluor ( I hear that this may be a bonus for a J stone, yes?)

Thanks everyone!

 

[lisa1.01fvs1]

I had a lot of guestions about the HCA as well and Garry commented on my results.

However, please read Goog Old Gold''s "Consumer''s Guide to the HCA" under technologies.

I think the stone deconstruction analysis neccesitates a degree in advanced physics; but you''ll get the overall jist that there is way more than meets the eye to cutting parameters.

I know many on PS use the tool in addition to others but it is a tool -- seeing the real diamond is the best test.

I hope that helps.

Lisa

 

[lisa1.01fvs1]

Oh and you can read about flourescence here on PS.

Sometimes it can make a yellower stone appear more white as blue and yellow impact each other on the color spectrum.

 

[Lorelei]

The diamond you mention looks like it falls into the shallower range for crown and pavillion angles, which could mean it is a very bright diamond. However the HCA may predict this, it can't take into account the individual personality of the diamond, your taste may run towards this diamond, or one which has scored between 1 and 2 on the HCA, beauty is in the eye of the beholder. The HCA score means this diamond is worthy of further consideration, so then you need an Idealscope image and a photograph of the diamond may be useful too, to evaluate this diamond.

Yes, medium blue fluorescence can help a lower colour diamond face up whiter, a J with med blue is a nice combo!

 

[Ellen]

I will also add, overall shallow stones can also suffer from head shadow, and may lack a bit in contrast and scintillation.

 

[bem3231]

While I am certainly no expert on HCA, when I began looking and discovered this tool I, too, had many questions. When I did some further research on it I discovered exactly what has already been mentioned in this thread - that HCA is but one of several tools available to evaluate a diamonds performance, the most important being your eyes! I have read several places that many people actually prefer the look and performance of diamonds in the 1 - 2 HCA range rather than those below 1.

 

[Jeanne61]

Thanks everyone.

I took a look at that GOG Technology page - what a gold mine of information! So, from what I gather, the HCA favors shallow stones which are great for jewelry to be viewed 12-16 " away.

I also found this thread https://www.pricescope.com/community/threads/too-shallow-with-great-hca.13670/ also about a shallow stone with a good HCA score. In it, Garry confirms the shallow stones are good for pendants and such, but also mentions that they''re "also not for people with dark skin or with lots of dark hair" (Garry, apologies if I misquoted you

). Why would that be?

 

[Lorelei]

Date: 1/29/2008 3:48:33 AM
Author: Jeanne61
Thanks everyone.

I took a look at that GOG Technology page - what a gold mine of information! So, from what I gather, the HCA favors shallow stones which are great for jewelry to be viewed 12-16 ' away.

I also found this thread https://www.pricescope.com/community/threads/too-shallow-with-great-hca.13670/ also about a shallow stone with a good HCA score. In it, Garry confirms the shallow stones are good for pendants and such, but also mentions that they're 'also not for people with dark skin or with lots of dark hair' (Garry, apologies if I misquoted you

). Why would that be?

Garry will correct me if I am wrong, but I think it is because a person with lots of dark hair etc can block some light from reaching the diamond, and the shallower type of diamond doesn't cope well with it, it may look dark and lose some sparkle if used in a ring setting ( head obstruction). Also if I remember rightly, these stones make good earrings and pendants for such people, as the head obstruction doesn't happen when they are worn in this way.

Hopefully Garry will chime in and give you a better explanation, but I think this is the reason why. Check out this page, to see a video on this in action.

http://diamondscope.pricescope.com/

 

[Garry H (Cut Nut)]

Good interpretations, but here is the low down - it is linked just where you get your HCA result (I guess it is too hard to find?

http://diamonds.pricescope.com/ideal.asp

 

[Lorelei]

* smacks head* I forgot that was where the info was listed

, thanks Garry!

 

[Garry H (Cut Nut)]

 

[Garry H (Cut Nut)]

 

[Lorelei]

 

[Jeanne61]

Lorelei, Garry - thanks for the translation and the education continues

This is a GIA cert stone and the specs are:

.68, J, VS2
depth = 59.9
table = 56
crown < = 33.5
pav < = 40.4
crown height = 14.5
pav depth = 42.5
polish & symmetry = excellent
GIA Cut = Very Good
AGAGrader = 1B
Fluor = Med Blue

From the page Garry posted, it says the GIA Facetware has rounding errors. Does that mean the GIA assigned Grade isn''t accurate due to the round-off? or that the numbers themselves are ''off''?

BTW - how does this stone look from the specs? It''s not an in-house stone so if I want to have it looked at, I''d have to have it called in for inspection. Price is approx $1500. Worth a look?

 

[Garry H (Cut Nut)]

it is not for a ring - it can be good for pendants though.

Consider up the colour and drop the clarity?

 

[Jeanne61]

Hi Garry,

It''s indeed for a pendant - so the shallower cut may be fine.

I''d actually prefer a stone with better color and trade-off on clarity. However, I''m looking for a stone to upgrade to, and my vendor doesn''t have anything in-house in my price range and specs right now - that''s why I''m looking at virtual stones. Ideally I''d want an in-house .55-.65 I-J (K is OK even if it faces up white enough), eyeclean SI1-SI2, with VG-Ex symmetry and polish and Ex cut, $1000-$1500 (ish)

Seems right now my online vendor''s in-house inventory is low ... guess I''ll keep looking until I find one closer to my specs.

Does anyone know: If I find an in-house stone offered by another vendor, can it be ''acquired'' by my vendor for my purchase? I''m betting not - sounds convoluted even to me!]

 

[Garry H (Cut Nut)]

Well then I have no p[roblem - the stone will face up better colour than it should be, and it is just under the 0.70ct price point but will spread bigger than many 70''s

 

[strmrdr]

do you have an IS image?
Or what does the GIA cert say the lower girdles are?

angles should make for an exellent pendant stone.

 

[Jeanne61]

Thanks Garry - BTW - what would be the .70 price point for a stone of this spec?

Strmrdr, no I don''t have an IS image for this stone yet. It''s not an inhouse stones so I''ll probably have to get the vendor to call it in to get all the neato pics.

The stone has a GIA cert, but the proportions plot doesn''t show a lower girdle length. The proportions from the cert is attached below. Can the length be determined from just these measurements?

I saw the GOG Lower Girdle video showing a longer lower girdle (~82%) can give the stone better pinfire. But won''t this also make the stone deeper than an ideal cut?

 

[strmrdr]

the 80% is the lgf% well a rounded version so its atleast 77.5
which is just where it needs to be for the c/p angle.
sounds like a really nice stone.

 

[Jeanne61]

Thanks for the interpreting strmrdr. What do you think of this one? Its comparable size to the first stone, but is an I, SI1. Again, no IS image or additional pics are avail because it''s a virtual stone.

 

[Jeanne61]

Sorry - forgot to mention that this second stone scored 1.3 EEEV on the HCA and is in BOTH the ''ideal'' zones! Might also be worth a look?

 

[strmrdr]

nice fic will be a very fiery stone.

The 2 stones would have different looks with the first being bright and the second fiery.

 

[Jeanne61]

Darn! That''s always the case isn''t it - one or the other! If I want to be greedy and want the best of both world, what kind of dimensions would I need to look for taht would give me more balance?

 

[strmrdr]

one of gog''s h&a''s, one of Paul''s Infinity''s, or a WF aca or other super-ideal RB''s are generally well balanced.

Frankly I think you are on the right track with these 2 for a pendant.
Save some money and get an awesome stone.
Just decide which you like slightly more fire or white light return.
Id go for the fic myself in a pendant

 

[Jeanne61]

Sound advice...I''ll wait one more week to see if anything comparable in price and quality show up inhouse. If not, I''ll have these 2 called in.

Thanks!