Valuing the relative importance of "grade" in the HCA...

[Regular Guy]

I suppose this is all academic (is it?), but I find I''m influenced, i.e., heartened or disappointed from one HCA score to another, when seeing the categories for "light return, fire, scintillation, and spread" going from Excellent to Very Good, etc.

Is there any way to say, by way of analogy, how much of a difference this makes?

For example, is this variation sort of like the variation you would find with a Brilliancescope?

Or...what would you you trade one or two very goods for, to get an excellent. Let''s say you were looking at two White Flash stones...

...(I bet this is sort of like Dave Atlas''s question?)

one was an "A Cut above" stone rating 3 excellents and a very good, and one was a Value stone, rating 4 excellents...which one would you choose, all things being equal? Where would the balance point be...what if it was 2 Very Goods on the branded stone, against 4 excellents on the value one? And, is one of the 4 categories (i.e., light return, fire, etc.) valued more than another?

Obviously, more data is needed...but you get the idea. What are these variations worth, relatively?

 

[valeria101]

I would say this is very "academic" - especially if you are a statistician or work with stats...

All those nice words ("excellent", "good") are nice and tempting, but to me the only relevant part is what the fine print says: "scores above two are OK. and for any fner detail take an Ideal Scope".

Aside this, that "spread" score matters the least to me - since it is based on some estimated size that''s probably even less precize than the diameter measurement on the cert. But this is not important given the previous statement.

All just IMO, of course.

 

[Regular Guy]

Shameless thwack (on behalf of Keneau Revees...and Bill & Ted''s Excellent Adventure!).

 

[oldminer]

Obviously differences in value occur below the level at which we can visually observe any differences. How to understand the scale of the HCA is part of the mystery of understanding diamond grading and related prices. Is a .9 visually better than a 1.1, or only philosophically better?

Where are the visiual demarcations and where are the value demarcations? Do they differ? I imagine they do, but how do we assess this?

 

[Regular Guy]

Thanks Dave,

I guess you're in substance answering the question, by setting up the example, comparing .9 to 1.1.

I know the difference is relative...I was just trying to get at, are we talking nieces, or third cousins once removed.

In the real world, I think the question is a bit less about "exactly what should I pay for that stone," but rather...between two or three reasonably good options, which one should I pick? So, it's from that point of view that I set up the White Flash example, above. And so, when you are shopping at a distance, when being presented with variations in grade, how to "value" that, relative to other things in consideration.

 

[oldminer]

When buying sight unseen, I''d say buying "better" is safer so long as your budget can afford the difference, if any.

When buying, in the flesh, with the diamonds in front of my own eyes, I would not decide based on unseen or invisible differences. That''s personal as some people and some cultures value perfection more than myself.

I doubt I could tell if a diamond was .9 or 1.1 HCA. Maybe Garry Holloway could. Somehow I sort of doubt he can discriminate that finely, but he might tell us otherwise. I would not make the HCA the final decision making tool, if two stones were very closely rated, unless I had nothing else more meaningful to go on. The HCA is part of the process, not the process itself.

 

[valeria101]

Is there a difference between HCA 1.1 and .9? I thought the "above 2" interval proposed by Garry is sort of a confidence interval...

Anyway, reading any scale is a taugh to crack problem of psichology rather than math.

There must be some way to reconcile "buying sight-unseen" and "in person" as you decsribe them. Any thoughts?

Fot a confessed inexperienced buyer like me, refference stones make all the difference in the world: once you take that off the pocked, what you see is a perfect example of "the best" in the very same light and background conditions as the sample to judge.

Could anything akin to a "refference stone" be constructed as a virtual model ? The important part is to let each viewer appreciate the difference between what they have and the refference - no scores, no scales. At least by my 0.2 IMO.

 

[Garry H (Cut Nut)]

This morning i was sitting in the bath analysing my belly button lint and I decided that i could learn more about my life than by considering the things you ask Ira (

)

I am hoping to redo HCA completely - since it was done I have learned a lot and it would be easier to completely redo it than to tinker. I have learned a lot more since 1999/2000, and have some very smart friends and associates.

Now I do not think redoing it will create any big changes to the overall grade - but it would change some parts - like fire and scintillation for example.

But if I can attempt to divert you to say consider this:

Say 2 diamonds with equivalent HCA scores - one has a 32 crown angle (about 41.1 pavilion) and one has a 36.5 crown angle (about 40.5 pavilion) - they will have a very different look and spread. Which is better? Consumers choice.

 

[valeria101]

Date: 12/3/2004 5:13:44 PM
Author: Garry H (Cut Nut)

But if I can attempt to divert you to say consider this:

Say 2 diamonds with equivalent HCA scores - one has a 32 crown angle (about 41.1 pavilion) and one has a 36.5 crown angle (about 40.5 pavilion) - they will have a very different look and spread. Which is better? Consumers choice.

Consumer choice... has this disturbing habit to turn up completely random, even for less subtle things

 

[Regular Guy]

Just in case anyone was on the edge of their seats....

Garry, I think you helped me to understand (without really intending to do that, at all), that what I was perceiving as two sets of data....

a) the HCA score, and
b) the grading data, ranging from excellent to poor...

is really only one set of data, with the composite of (b) yielding (a).

I could see that easily, finally (as you obliquely pointed to your old research), by looking at your other site showing your detailed work on the HCA; previously, I had only been there to read about FICs, but I do see the other background there, which at least serves to clarify my original question.

And, speaking of which...not that I really do understand any of this (and of course good luck with any reformulations, by the way), but...regarding the two different diamond looks you juxtapose above, are you pointing to anything other than the separation by type you have already laid out between BICs and FICs?

Now, back to belly button analysis.

Regards,

 

[Regular Guy]

BTW, presuming you were working with today's options, wanted a 1.5 carat diamond, GH in color, and SI 1 was OK, is the basis upon which you'd select either of these options from DCD clear, or would you just want to see them both? If you could only see them one at a time, which would you select first?

http://www.dirtcheapdiamonds.com/diamond_detail.cfm?did=7034714&ref=PS622

http://www.dirtcheapdiamonds.com/diamond_detail.cfm?did=7034699&ref=PS622

(edited to add: Lachance22 might like to know, too!)

 

[oldminer]

Garry is now busy working on the BBLA, belly button lint advisor, as well as contemplating the more important things in life. The work on the new HCA will just have to wait.

 

[Garry H (Cut Nut)]

he he he

We should not take ourselves too seriously kiddies

ira both are very nice stones.
I would probably prefer the one with the fatter star - but want to check the ideal-scope to see the brighter upper girdles are not dug out (leaking)