HCA spread of very good vs. excellent

[rosy]

Hi, Ive noticed that the majority of diamonds I run through the HCA receive a score on spread of very good. I recently ran one & for the first time it returned a spread of excellent. How does the very good spread vs the excellent spread affect the appearance of the diamond?

 

[Garry H (Cut Nut)]

one with excellent spread will be bigger - but it will tend to be shallow and will be a little dark when viewed from closer than 12 inches

 

[rosy]

What if the diamond scores a 1.4 on the HCA, would it still look dark from 12 inches away? I had a diamond that scored .9 with a spread of very good & it looked dark from 12 inches away.

Does this mean I should stick with a diamond with a very good spread instead of excellent?

 

[rosy]

bump

 

[valeria101]

Just my 0.2 worth...

Those scores are as good as the numbers you put into them - meaning... not very precise. The "spread" score guesses the size of the stone, but that is written black on white on the lab report in simple milimeters instead of complicated score points

As far as I know, contrast is a finer detail - two relatively close HCA scores (like those you mention) make a rather rough guess at it. The proportions of minor facets is not taken into account by the HCA (or the AGS0 standard, for that matter) but they surely make a difference when "superideal" precission is considered. Down this link are some examples of what I am talking about...

Since seeing these two is probably too much to ask online, how about ideal scope pictures? Any luck ?

 

[rosy]

Unfortunately I don''t have an ideal scope image available. I''m really not sure what to do. I really did not like the up close darkness of my other diamond that scored a .9. & I''m afraid that this will be similar to that.

 

[valeria101]

Date: 12/30/2004 12:29:28 PM
Author: rosy

I really did not like the up close darkness of my other diamond that scored a .9. & I''m afraid that this will be similar to that.

Are the diamonds presented with ''scope pics way over the price of those by numbers only that you are looking at ? Aside that and inspecting stones one by one in person, no idea how to avoid the respective look

 

[RockDoc]

Date: 12/30/2004 12:56:11 PM
Author: valeria101

Date: 12/30/2004 12:29:28 PM
Author: rosy

I really did not like the up close darkness of my other diamond that scored a .9. & I''m afraid that this will be similar to that.

Are the diamonds presented with ''scope pics way over the price of those by numbers only that you are looking at ? Aside that and inspecting stones one by one in person, no idea how to avoid the respective look

The HCA results are based on Gary''s standards, which necessarilly don''t agree with industry standards.

Also it is modeled after what he believes is "real world results". The problem with this is the HCA doesn''t examine the actual stone, and while its a useful help in checking stones you find on the net without having the stone available to examine, it is only a partial indictcation of what the stone may actually be.

I''m not trying to concern you or frighten you, but having the stone (or stones) examined in person is a very priudent idea before you pick one.

To answer your question, It may be better to go with the very good rating given the excellent one might be a better stone.
Wish Gary would change his parameters to an accepted industry standard.

Rockdoc

 

[rosy]

Date: 12/29/2004 5:41:36 PM
Author: Garry H (Cut Nut)
one with excellent spread will be bigger - but it will tend to be shallow and will be a little dark when viewed from closer than 12 inches

Would the darkness still occur if the diamond were in the D-E-F range?

 

[RockDoc]

It depends...........

Rockdoc

 

[Serg]

Date: 12/30/2004 1

8:30 PM
Author: RockDoc

Wish Gary would change his parameters to an accepted industry standard.

Rockdoc

What is an accepted industry standard?

I missed something? Santa Claus brought industry standard?

 

[strmrdr]

Date: 12/31/2004 6:45:30 PM
Author: rosy

Date: 12/29/2004 5:41:36 PM

Author: Garry H (Cut Nut)

one with excellent spread will be bigger - but it will tend to be shallow and will be a little dark when viewed from closer than 12 inches

Would the darkness still occur if the diamond were in the D-E-F range?

yes.
Its a function of how its cut and returning light not the color of the material thats causing it.

 

[rosy]

Okay, thanks. I think I read on some earlier posts that someone had an E colored diamond that was behaving the same way, looking dark in certain lightings due to shallowness. If that''s the case I feel theres no use for me to go up in color, I think I just need to look for a stone that''s not as shallow or accept the shallowness. It seems like most stones I run through the HCA have been in the .9-1.2 range. Difficult to find one closer to 2. Oh well, they all say it''s just splitting hairs on anything under a 2 anyway. Gonna just buy the diamond & get on with my life.

 

[Garry H (Cut Nut)]

Date: 12/29/2004 10:21

9 PM
Author: rosy
What if the diamond scores a 1.4 on the HCA, would it still look dark from 12 inches away? I had a diamond that scored .9 with a spread of very good & it looked dark from 12 inches away.

Does this mean I should stick with a diamond with a very good spread instead of excellent?

Rosy have been away for a few days of NY partying

If you want to be sure the diamond will look good close up, then stay in the upper zones on the haca chart.

You will see you can have an HCA under 1.0 with Crown31 and pavilion 41, or Crwon 34 P 40.3
Both these stones are in the shallower ranges and will look better from a distance - they are perfect earring and pendaant stones.

On the other hand, diamonds tending to be steeper, like C34 P40.9 get a worse score for spread so they will natirally get a higher HCA score. This is not an industry standard because the industry is not as smart as consumers. So far it has no accepted standard - although Serg has introduced one - the modern tolkowsky with + and - wt and % that is given on DiamCalc.

So if you removed the spread factor, you would find that an HCA score for the deeper diamonds often presented as "ideal cuts" would actually score a similar result to the shallower ones I am often accused of favouring.

So in short - you can have very different looking diamonds with the same HCA score. For instance a steep 36.5 crown and 40 pavilion will rate very low - but will not be as bright but have more facets appearance and many little sparkles of fire. 9but they are almost impossible to find because people like Rocdoc will say they are no good. They are wrong. And eventuaally the industry will wake up.

 

[Garry H (Cut Nut)]

Date: 1/1/2005 3

7:24 AM
Author: Serg

Date: 12/30/2004 1

8:30 PM
Author: RockDoc

Wish Gary would change his parameters to an accepted industry standard.

Rockdoc

What is an accepted industry standard?

I missed something? Santa Claus brought industry standard?

Thanks Sergey, I had a good laugh at that.

 

[rosy]

If I have a diamond that rates 1.2 ex ex ex ex, would this be more suitable for a pendants or earrings rather than a ring?

 

[Garry H (Cut Nut)]

Rosy you are not getting it.

1.2 can be north south east or west on the HCA chart.

If you want a bargain stone that looks great and looks very big in a pendant, then look for stones that come up in the lower left on the HCA chart - but do not go below 2.

 

[flowergurl]

CutNutdo you mean the red part of the lower left? What about 32deg and 40.8deg? I thought the red area was good. How far south are you talking? Could you define the "lower part of the chart"? Thanks

 

[Garry H (Cut Nut)]

any part that is still under 2.0 (i.e red)