HCA Rating with Pavilion Angle of 41 vs 40.8

[Cheburashka]

Hello All!

I am very curious to know if the GIA measurement of the crown and pavilion angles is truly accurate. I recently purchased a diamond. I'm very happy with my purchase. It's measurements are:

55% Table
61.9% Depth
35* Crown Angle
41* Pavilion Angle

When I use the HCA tool, i get this chart 1. When I change the pavilion angle to 40.8, chart 2 is completely different. Which makes me wonder if a diamond can lose so much of it's performance from a mere .2* change.

Looking forward to hearing your input. Thank you.

 

[Karl_K]

HCA in general is overly harsh on pavilion angles of 41 degrees.
In a lot of cases they are just fine.
An IS/ASET image would tell for sure.
In some cases a .2 can make a large difference.
Remember the numbers on a gia report are rounded then averaged then rounded again.
The lgf%/lgh% makes a large difference also.

 

[yssie]

Hello All!

I am very curious to know if the GIA measurement of the crown and pavilion angles is truly accurate. I recently purchased a diamond. I'm very happy with my purchase. It's measurements are:

55% Table
61.9% Depth
35* Crown Angle
41* Pavilion Angle

When I use the HCA tool, i get this chart 1. When I change the pavilion angle to 40.8, chart 2 is completely different. Which makes me wonder if a diamond can lose so much of it's performance from a mere .2* change.

Looking forward to hearing your input. Thank you.

The sarin scanners AGS uses (as of late 2011 anyway) are accurate to +/- 0.1deg, don't know about GIA but I assume it's the same. GIA also rounds pavilion up to nearest 0.2deg, so that 41 could be 40.9...

Other info on the proportions diagram and date of report, or post GIA report number and exact ct wt listed on the report?

So no, 40.8 vs 41 is definitely not something to scratch a stone from the list over, but I always recommend having the loose stone shipped out to you to inspect before having it set.

 

[Cheburashka]

Here is the other info from the GIA report.

 

[Cheburashka]

::bump::

 

[Regular Guy]

Ah...for the good old days...

https://www.pricescope.com/community/threads/41-degree-pavillion-angle.65301/


Ira Z.

 

[yssie]

Here is the other info from the GIA report.

Cheb, everything on the report is fine we'd need more info - a full scan, some pics - to give you more detailed info though.


Ira - nice thread!

 

[Dreamer_D]

That stone looks like a cracker jack to me.

 

[Karl_K]

Here is the other info from the GIA report.

With that lgf%/lgh% of 80% anything in the GIA rounding should be fine.
The next step is images, the numbers have told you everything they can.
IS or ASET images are preferred and if h&a is claimed it needs to be backed up with heart images.

 

[Cheburashka]

Here is the other info from the GIA report.

With that lgf%/lgh% of 80% anything in the GIA rounding should be fine.
The next step is images, the numbers have told you everything they can.
IS or ASET images are preferred and if h&a is claimed it needs to be backed up with heart images.

It was never claimed that it was a H&A stone. Unfortunately, I don't have any images. I wish I did. However, I don't see myself paying to get those images. Last night I did use the cut grading tool and the stone came out top be a 1B. I'm satisfied with that. Hopefully this stone will not be my last diamond purchase and maybe the next one will be H&A.

BTW, what does "It looks like a cracker jack to me" mean? Does that imply its good or that it's just like every other one? I'm not offended, just curious.

 

[Regular Guy]

BTW, what does "It looks like a cracker jack to me" mean? Does that imply its good or that it's just like every other one? I'm not offended, just curious.

https://www.google.com/webhp?source....,cf.osb&fp=a19adc643edab6bb&biw=1600&bih=788


Ira Z.

 

[Dreamer_D]

Here is the other info from the GIA report.

With that lgf%/lgh% of 80% anything in the GIA rounding should be fine.
The next step is images, the numbers have told you everything they can.
IS or ASET images are preferred and if h&a is claimed it needs to be backed up with heart images.

It was never claimed that it was a H&A stone. Unfortunately, I don't have any images. I wish I did. However, I don't see myself paying to get those images. Last night I did use the cut grading tool and the stone came out top be a 1B. I'm satisfied with that. Hopefully this stone will not be my last diamond purchase and maybe the next one will be H&A.

BTW, what does "It looks like a cracker jack to me" mean? Does that imply its good or that it's just like every other one? I'm not offended, just curious.

LOL... that means it looks awesome Maybe it is a Canadian saying. I have owned many diamonds and I do enjoy the precision of H&As, but I do think its mostly a "mind clean" thing, a preference that most people cannot see with their own eyes. As storm said, the longer lgf will compensate for the PA, something the HCA does not include in its calculations. That is why you must always rely on all the information available to make a choice, not any one tool.

 

[Regular Guy]

As storm said, the longer lgf will compensate for the PA, something the HCA does not include in its calculations. That is why you must always rely on all the information available to make a choice, not any one tool.

Dreamer, Storm...or...can anyone direct me to a useful tutorial, whether an e-mail string here, a vendor site, or other...that helps provide info on the interactivity of these other data points (i.e., lgf, etc,) not included in HCA, but with predictable influence on performance?


Ira Z.

 

[yssie]

Ira have you seen this page? I found it super useful - http://www.goodoldgold.com/Articles/MinorFacets/

And also Karl's article https://www.pricescope.com/journal/do_pavilion_mains_drive_light_return_modern_round_brilliant