The Differences in Appearance Within GIA Diamond Cut Grades

[Garry H (Cut Nut)]

its 5.50am here.
I can not understand your ??? IRa?

 

[Regular Guy]

No rush, mate; thanks for the quick reply!

I suppose there''s two items here, and the second one has 3 parts, representing the question for you:

I - This is just a change in view of what GIA is doing. If we reduce our expectations, and just seek the benefit of their now reporting of data (rather than seeking much benefit from their 5 grades particularly), we can reap the benefits, and try to take advantage of their now simply reporting data on the diamonds they''re grading. No longer will you see post after post here saying: get a sarin.

II -- Of course, this change of view will require some minor to major tweaking of existing tools, to gain the benefit sought. That''s where your help will come in.

Presuming GIA''s output will look like this:

Table size: 54%
Crown angle: 34.0°
Pavilion angle: 40.8°
Star length: 50%
Lower-girdle length: 75%


a) without any further work from you, can simple translations be put in place to

1) reinterpret crown & pavilion angles into percentages
2) combine with inferences from the girdle info that will be reported also, (right?),
3) to come up with a total depth percentage
4) allowing us to use the HCA, unmodified.

b) revise the HCA to do what (a) is attempting to do.

c) optimize...incorporate in HCAII the data further gathered, to include star length, and lower girdle length, so that the inclusion of that information will be factored into the evaluation of the diamond in question

After all, Garry, you''ve already put in your to do list the plan to provide a time limited, pay for use HCA delivered to a PDA. While you''re at it, maybe you can just tweak it thusly.

Perhaps GIA is not done, and their output will be different than that reviewed above. However, if it is like this, bolded above, and if it''s reasonable to both question the value of their own interpretation of their collected data, a significant benefit can be realized from the data they will begin to present, so long as it can be read with acuity.

Thanks in advance for your help.

 

[Garry H (Cut Nut)]

Date: 5/3/2005 4:24:14 PM
Author: Regular Guy


Table size: 54%
Crown angle: 34.0°
Pavilion angle: 40.8°
Star length: 50%
Lower-girdle length: 75%


a) without any further work from you, can simple translations be put in place to

1) reinterpret crown & pavilion angles into percentages No one should ever use %''s ever again - they mean nothing. Manufacturers rarely use %''s (except in choosing crown heights for pots)
2) combine with inferences from the girdle info that will be reported also, (right?), Yes - subtract crown pav and table from total depth and you have girdle thickness in % which GIA probably will never use - their system works fine.
3) to come up with a total depth percentage They should still give it (it can be calculated anyway)
4) allowing us to use the HCA, unmodified. of course

b) revise the HCA to do what (a) is attempting to do.still do not understand you?

c) optimize...incorporate in HCAII the data further gathered, to include star length, and lower girdle length, so that the inclusion of that information will be factored into the evaluation of the diamond in question The next release of DiamCalc and Gem Adviser will make such approaches only useful for manufacturers - and the answer is "Yes, there is a plan for an HCApro, which will be more useful for cutters"

in addition I have heard no plans that GIA nor AGS will be publishing predictive scores for Brilliance, Fire or Scintillation and Spread that I believe can be estimated from any diamonds proportions - but that is better done with Sergey''s approach than what I can effectively do.

After all, Garry, you''ve already put in your to do list the plan to provide a time limited, pay for use HCA delivered to a PDA. While you''re at it, maybe you can just tweak it thusly.

 

[Tony S.]

I am meeting my jeweler tomorrow and she is going to give me the crown and pavilion measurements so we can figure out where the cut of the diamond I am purchasing would fall out on the AGS cert. How do you recommend I proceed given this new information that was released from GIA??? Should I tell her I want her to perform the measurements based on this new info? I am a novice so this is all confusing to me.

 

[valeria101]

Date: 5/3/2005 10:21:49 PM
Author: Tony S.

How do you recommend I proceed given this new information that was released from GIA??? Should I tell her I want her to perform the measurements based on this new info? I am a novice so this is all confusing to me.

The catch of these new grades is that no one but GIA can give them - the tools needed and the procedures remain with GIA.

Not that the old "ideal" standard from AGS was any different - just less intricate so that some prediction had became fesible in time.

You can definitely use one of the existing tools (HCA, Ideal SCope, Brilliance SCope... you name it) to evaluate cut. The new grades are still in the pipeline. Unless you are a GIA fan and want their autograph, I would not worry about them - what will come will come and a diamond that is brilliant today will stay that way.

The research used by GIA to get to their new grades has been around for quite some time - the new grades are not all that new. Sure enough, the new new ideals will not come at a discount: if they will be better in any subtle way from the current ideals is more a matter of theoretical debate than practical concern. Well, at least as far as I understand.

Hope some of this makes sense

 

[Regular Guy]

Date: 5/3/2005 9:11:59 PM
Author: Garry H (Cut Nut)

Date: 5/3/2005 4:24:14 PM
Author: Regular Guy


Table size: 54%
Crown angle: 34.0°
Pavilion angle: 40.8°
Star length: 50%
Lower-girdle length: 75%


a) without any further work from you, can simple translations be put in place to

1) reinterpret crown & pavilion angles into percentages No one should ever use %''s ever again - they mean nothing. Manufacturers rarely use %''s (except in choosing crown heights for pots)
2) combine with inferences from the girdle info that will be reported also, (right?), Yes - subtract crown pav and table from total depth and you have girdle thickness in % which GIA probably will never use - their system works fine.
3) to come up with a total depth percentage They should still give it (it can be calculated anyway)
4) allowing us to use the HCA, unmodified. of course

b) revise the HCA to do what (a) is attempting to do.still do not understand you?

c) optimize...incorporate in HCAII the data further gathered, to include star length, and lower girdle length, so that the inclusion of that information will be factored into the evaluation of the diamond in question The next release of DiamCalc and Gem Adviser will make such approaches only useful for manufacturers - and the answer is ''Yes, there is a plan for an HCApro, which will be more useful for cutters''

in addition I have heard no plans that GIA nor AGS will be publishing predictive scores for Brilliance, Fire or Scintillation and Spread that I believe can be estimated from any diamonds proportions - but that is better done with Sergey''s approach than what I can effectively do.

After all, Garry, you''ve already put in your to do list the plan to provide a time limited, pay for use HCA delivered to a PDA. While you''re at it, maybe you can just tweak it thusly.

Gary, thanks for getting back.

Apart from wanting to re-express the recognition that the new GIA certs will capture data, so this is good...most of my points above were based on it not having been obvious to me that they would also include total depth info. So most of my notes above in both (a) and (b) you were responding to, had to do with contemplating the strategies that may be necessary to reconstruct their data, so HCA can be still used. Sounds like that whether included (as you think it will be) or not, it can be done.

Good wishes,

 

[Paul-Antwerp]

Is it sure that GIA will put actual average angles on the grading report?

 

[Regular Guy]

"Is it sure that GIA will put actual average angles on the grading report?"

Really, I''m not sure of anything, but since I re-introduced this post, I''ll bite...

Earlier, you wrote...

Date: 4/16/2005 8

7:19 AM
Author: Paul-Antwerp


Secondly, there is a huge difference in grading approach. GIA is using averages of measurements, checking these (in a rounded form) in their charts (which are a result of their studies), and thus come up with a grade, entirely based upon average parameters. AGS, on the other hand, is taking a full 3D-scan of the stone (with a measurement of each individual facet) and will take this scan through their ray-tracing software. Stones with identical average parameters will get different grades by AGS, because of the differences of individual facets. This last approach allows AGS to also start cut grading for fancy shapes (princesses) now, whereas the GIA-approach will not end up in meaningful results for fancy shapes.

Is the suggestion -- independent of what GIA could be doing as opposed to what AGS is doing -- that their report of crown & pavilion angles would be anything other than a recording of what could at least be routinely picked up today from a report from sarin?

 

[Garry H (Cut Nut)]

GIA will definitely be putting data on their reports and making this info freely available so manufacturers know what to do to achieve their grades