hca .5 vs 1.5

[rosy]

Hi,
There is a disclaimer on the HCA that "you may prefer a 1.5 score vs. a .5 score". What effect does a score of 1.5 have on the diamond that is different than the .5?

 

[Garry H (Cut Nut)]

Most stones under 1.0 are tending to shallow (low spread panalty) and if you can focus as close up as 6 inches you may find these stones appear too dark.

 

[Paul-Antwerp]

Although, Garry, with a 0.5-score, it is not necessary to have a shallow stone, it is just a possibility.

I would prefer to describe it as such:

The HCA is a system that is working on a number of conditions, and gives a score according to the best of these conditions. Some of these conditions are:
- a completely symmetrical stone
- the same angle all around the stone
- the best possible length of lower girdle facets
- the best possible size of stars

If the above conditions are met, generally a lower score will give a higher light performance, but the stone needs to be checked to verify that. In any case, with two scores close to eachother (and 0.5 and 1.5 are close), it is entirely possible that the higher HCA-score meets the above conditions less well, and you have a lower light performance.

In a way, you should take the HCA-score as indicating the theoretically highest possible score if all other criteria are met. Just like you can have a car with one having a higher top speed than the other, while in a race, with a less good driver, that car will not finish first.

Garry, it may not be entirely correct, but I think that it is close, isn''t it?

Live long,

 

[valeria101]

Date: 11/2/2004 9:27:34 AM
Author: Paul-Antwerp

In a way, you should take the HCA-score as indicating the theoretically highest possible score if all other criteria are met.

This can be read as "the HCA overestimates actual performance". I am sure this is not what you meant...

 

[rosy]

Date: 11/2/2004 6:29:19 AM
Author: Garry H (Cut Nut)
Most stones under 1.0 are tending to shallow (low spread panalty) and if you can focus as close up as 6 inches you may find these stones appear too dark.

Hi Garry,
To clarify, if I have a stone that rates like this:

Light Return: Excellent
Fire: Excellent
Scintillation: Excellent
Spread: Very Good
HCA score: .6

Is the very good on spread meaning it is a shallow stone?
In this case when comparing to a 2.4 scoring diamond which would be the better choice?

 

[Paul-Antwerp]

Date: 11/2/2004 11:32:17 AM
Author: valeria101

Date: 11/2/2004 9:27:34 AM
Author: Paul-Antwerp

In a way, you should take the HCA-score as indicating the theoretically highest possible score if all other criteria are met.

This can be read as ''the HCA overestimates actual performance''. I am sure this is not what you meant...

Valeria,

Take it as the measurement of the top speed of a car. Or even better, the gas mileage. It is a theoretical score, based on limited information of averages. Not every driver will come close to that theoretical figure, just like not every cutter will deliver light performance, even with a very high HCA.

In a way, the HCA-score is always over-estimated, although with this being a relative score between 0 and 10, this does not make any difference.

Rosy,

with a ''very good'' on spread, I think that this is a stone that received such a high HCA on its merits, not because it gets some kind of extra plus, because of it being shallow, thus more spready. It is exactly the kind of example, that I mean, when I tell Garry, that it is a possibility to get a high HCA because of being more spready, but not a necessity.

I would not be surprised, if you are talking about a stone, which we have cut ourselves.

Live long,

 

[valeria101]

Date: 11/2/2004 4

1:25 PM
Author: Paul-Antwerp

Date: 11/2/2004 11:32:17 AM
Author: valeria101

Date: 11/2/2004 9:27:34 AM
Author: Paul-Antwerp

In a way, you should take the HCA-score as indicating the theoretically highest possible score if all other criteria are met.

This can be read as ''the HCA overestimates actual performance''. I am sure this is not what you meant...

Valeria,

In a way, the HCA-score is always over-estimated, although with this being a relative score between 0 and 10, this does not make any difference.

Thanks

I can definitely understand this as a matter of conceptual consistency... as it should be.

 

[Garry H (Cut Nut)]

Good analagies Paul

Rosy do you see that HCA will not tell you a stone is great, only that it can be great - but it might not be - so it is a tool to narrow down the stones for further investigation.
Nothing wrong with a 2 that has been beautifully manufactured.