HCA can not help with ,,,,,,,??

[Photon]

Hi,

I understand HCA should be used to weed out bad stones, but i was wondering information can not be captured by HCA data? Lets say the HCA output is like 1.3-ex-ex-ex-ex. I am assuming it means it is an excellently cut stone with excellent symmetry. Am I on track so far? I am assuming it does not provide any feedback on the color, clarity, inclusions and polish. Is there anything else that HCA can and can not tell us?

Thanks
Photon.

 

[JulieN]

correction: angles are averages; HCA assumes the stone is symmetrical. of course, this is not always the case.

 

[Dancing Fire]

Date: 7/3/2008 2:44:05 AM
Author: JulieN
correction: angles are averages; HCA assumes the stone is symmetrical. of course, this is not always the case.

agree with JulieN....
always better to post a sarin or helium report.

 

[Photon]

I dont have access to sarin report yet but here are the numbers for one of the stones I was looking at.

Depth: 59.9 %
Table: 59 %
Crown Angle: 33°
Crown Height: 13.5 %
Pavilion Angle: 41°
Pavilion Depth: 43.5 %
Girdle: Medium, Faceted
Culet: None
Star length: 55 %
Lower Half: 75 %

What is the significance of Star Length and Lower Half?

Are you saying the percentages are more accurate than the angles? If I use angles I am getting 1-ex-ex-ex-ex, but if i use percentages i am getting 1.5-ex-ex-vg-ex. I understand they fall in the same range relatively, but the difference because of the rounding affect of angles?

Thanks
Photon.

 

[arjunajane]

Date: 7/3/2008 2:34:52 AM
Author:Photon
Hi,

I understand HCA should be used to weed out bad stones, but i was wondering information can not be captured by HCA data? Lets say the HCA output is like 1.3-ex-ex-ex-ex. I am assuming it means it is an excellently cut stone with excellent symmetry. Am I on track so far? I am assuming it does not provide any feedback on the color, clarity, inclusions and polish. Is there anything else that HCA can and can not tell us?

Thanks
Photon.

if you have the info to gain an hca score, supposedly you have already seen this stone in real life or online, so you will already have access to that info.

 

[Lorelei]

Date: 7/3/2008 3:07:52 AM
Author: Photon
I dont have access to sarin report yet but here are the numbers for one of the stones I was looking at.

Depth: 59.9 %
Table: 59 %
Crown Angle: 33°
Crown Height: 13.5 %
Pavilion Angle: 41°
Pavilion Depth: 43.5 %
Girdle: Medium, Faceted
Culet: None
Star length: 55 %
Lower Half: 75 %

What is the significance of Star Length and Lower Half?

Are you saying the percentages are more accurate than the angles? If I use angles I am getting 1-ex-ex-ex-ex, but if i use percentages i am getting 1.5-ex-ex-vg-ex. I understand they fall in the same range relatively, but the difference because of the rounding affect of angles?

Thanks
Photon.

Angles are more accurate than percentages. Also don't worry so much about HCA estimations such as ex ex vg etc, the HCA can't see the diamond, and a lower score isn't better than a higher one. You want to score 2 or below generally, then you evaluate using Idealscope and other methods, the HCA is used as an elimination tool, not for selection.

As to your query concerning star and lower halves, this page should help.

http://www.goodoldgold.com/Articles/MinorFacets/

 

[ikonos]

Those numbers appear to be like 60-60 that was mentioned in the tutorial. With out the benefit of IS and ASET pictures we may not know how it looks but some of the experts here might be able to tell you whether it is a well cut stone or not based on the above numbers confirming or denying your above assumptions.

I am also confused about the two statements from different forum members one saying angles are approximate and the other saying angles are more accurate than percentages. I hope you will get other opinions to clarify.

 

[Lorelei]

Angles are more accurate than percentages. Please see the following information copied from the HCA tutorial and useage.

"It is best to input crown and pavilion angles into HCA to reject less beautiful diamonds. We use trigonometry to calculate the angles from % data. Use angles if you have them because:

%'s are often rounded i.e. 13.3% crown height becomes 13% or 13.5%.
Pavilion depth % when converted to pavilion angle often understates the pavilion angle by 0.15°
Scanners are not good at measuring culets; a culet reduces the pavilion depth % but does not change the pavilion angle.
Sarin scanner data is better than Ogi because they calculate the angles and then scale of the %'s. Ogi works the other way round.

If you only have access to % info (e.g. EGL, IGI or HRD report) then use the %'s to reject known duds, then and ask the supplier to run Sarin angle data on your short list."

I hope this helps.

 

[Allison D.]

Date: 7/3/2008 4:17:57 PM
Author: ikonos

I am also confused about the two statements from different forum members one saying angles are approximate and the other saying angles are more accurate than percentages.

To help clear it up......

Julie''s comment says angles are averages; what she means is that the grading report may show a crown angle of 34.7, for example, but that doesn''t mean every crown facet is exactly 34.7. The facets may range from 34.3 to 34.9, and the average angle is 34.7. As long as the corresponding pavilion mains are complementary, it''s of minimal concern.

Angles are still more accurate than percentages, though, because the rounding is even more extreme when expressed as a percentage than as an angle.

Think of it this way: The average student may have 96 cents (some have 95, some 96, and some 97), but if you had to round to a full decimal percentage, everyone would be rounded up to $1.00. That percentage rounding is far more variant (less accurate) than taking the average.

(Granted, in this example, the average could be skewed if the spread between highest and lowest was bigger, but in a well cut diamond, there shouldn''t be a wide fluctation between the facets, so the 94/95/96 analogy should be fairly spot on.)