Cut Geeks only: HCA approved GIA Excellents

[Garry H (Cut Nut)]

Should I put some sort of notation on the HCA page to advise that GIA Excellent includes steep-deeps and stay below say HCA 2.5 ??????

Play with these charts (convenienlty upside down to all previous conventions)
http://www.diamondcut.gia.edu/charts/57_table.html

You should also be able to find actual Cut graded stone results for most stones from the past few years at this link http://reportcheck.gia.edu/ (but it has been down the past few days)
You need cert # and ct wt

 

[perry]

What I find interesting is that according to the index for the chart. P is Poor. However, there are no Poor cut diamonds on the chart.

It must be because all diamonds are "Fair" by definintion....

If I can''t trust GIA to tell me when a diamond is Poor in the cut grade department - why should I trust them to tell me that they are Excellent?

Perry

 

[Garry H (Cut Nut)]

Perry change the proportions of the table to 70% and there are plenty of Poors.
There are 3 tabs that allow you to make charts by different table, crown or pavilion angles.

I have done a 57% table size overlay showing GIA Ex and VG on HCA with AGS 0 included.

We can see that GIA have found the same "slope" (even though Ilene Reinitz once denied it back in WLR days). The trouble is their wierd lighting and tray have moved the result into steep deep territory (as shown by AGS as well as GH)

What would be really cool is to make an ideal-scope image for each GIA Excellent and blow their EX section on the chart up and put one ideal-scope image on each little square. The 62% table chart would be really scary.

 

[valeria101]

Date: 2/15/2006 6:45:42 AM
Author: Garry H (Cut Nut)


Should I put some sort of notation on the HCA page to advise that GIA Excellent includes steep-deeps and stay below say HCA 2.5 ?

Why the Hell not. The same thing done to the old AGS 'slot' caught pretty well. Some may still remember.

I have done a 57% table size overlay showing GIA Ex and VG on HCA with AGS 0 included.
What would be really cool is to make an ideal-scope image for each GIA Excellent and blow their EX section on the chart up and put one ideal-scope image on each little square. The 62% table chart would be really scary.


Sounds like my sort of thing (boring & geeky).

See attached to the next posts. (JPG looks relatively terrible compared to the BMP screenshots of DC pictures... dunno why.)

 

[Regular Guy]

Two primary thoughts, with the preface that...while the intention to take up getting ones hands dirty and helping others is admirable, in this particular case, given the implications of mucking with this other system, looking singularly at the consequences of measurement error, I wonder if the best solution would instead be to keep ones hands clean.

- So, for example, were you to comment in the HCA on applying GIA data to HCA, since you are talking at that point hopefully about actuals versus hypothetical crown & pavilion angle complements, knowing that GIA rounds data, unless you DID provide a value added legend (THIS could be helpful, as an add on for GIA readers) that showed, for any given angle, the possible actual angle represented by whatever data is posted on the cert...letting people know that even for GIA, the represented crown & pavilion angle could accurately (given their internal standards) point to a relatively significantly wider variance of angles...helping the user understand this handicap may be a first necessary step in commenting on the proposed interrelationship between these two systems.

- Given that the proposed user actually gets to your HCA chart to make use of whatever annotated text you have provided, unless you feel that the GIA system will have provided them some sort of upside protection otherwise, I'm not sure why you would want to give them the grace of an extra .5 measure of wiggle room, i.e., why suggest to them 2.5 is perfectly fine, vs. 0 - 2 for anyone else.

Finally, unlike Ana's intent, my thoughts are brought to you without the benefit of any actual work. As always, though, your efforts in these matters are appreciated.

 

[valeria101]

 

[valeria101]

 

[valeria101]

Date: 2/15/2006 6:45:42 AM
Author: Garry H (Cut Nut)


We can see that GIA have found the same ''slope'' (even though Ilene Reinitz once denied it back in WLR days).

Strange... ''Thought everyone agreed on that (how could they avoid it?).

Anyway, just wanted to drop the personal 2c after the impersonal charts: ... hope some day, someone finds a mine of diamond pancakes, so that RBCs get to err towards the lower-left corner of the HCA chart instead of the top right. At least those mistakes look nicer.

 

[valeria101]

 

[Garry H (Cut Nut)]

Thank you very much Ana - great job

Date: 2/15/2006 10:38:56 AM
Author: valeria101

Date: 2/15/2006 6:45:42 AM
Author: Garry H (Cut Nut)


We can see that GIA have found the same ''slope'' (even though Ilene Reinitz once denied it back in WLR days).

Strange... ''Thought everyone agreed on that (how could they avoid it?).

This is a partial direct quote from an article I submitted to Gems&Gemology - they refer to Figure 11 and the fact that I had noticed this sloping relationship from observing diamonds with Firescopes and my early Ideal-scope hand helds.(the black intersecting lines dran on Fig 11 are mine)

DISCOVERY OF A SIMPLE WAY TO QUANTIFY CUT
The patterns in Figure 11 in the Gems & Gemology paper by Hemphill et al. show a trend. The centre point of the oval ‘bull''s-eyes’ on the seven graphs for crown angles between 30.5* and 36.5* move from the top right to the bottom left. This trend confirms my simple system for buying, unseen, diamonds with the aid of Sarin reports.
(Please note that this is Mr. Holloway’s system, not one proposed or necessarily supported by GIA. Dr. Ilene Reinitz)
And .......
[I am not sure what Mr. Holloway means by this; we were certainly aware that the center moved to shallower pavilions and larger tables as the crown angle increased well before Symposium. Mary Johnson) (Furthermore, I am not sure that we agree with his “significance” as it is described below. Dr. Ilene Reinitz]

 

[Garry H (Cut Nut)]

This is a chart indicating Fire potential according to AGS.
I have included only the part that roughly lines up with the HCA chart proportions - note the lighter diagonal running from the lower right corner that represent more firey diamond proportions.
Same same

 

[valeria101]

Date: 2/15/2006 3:04:12 PM
Author: Garry H (Cut Nut)

This is a chart indicating Fire potential according to AGS.

It looks like to obtain an inverse relation between crown and pav angles, the only necessary input in the model is the shape of the cut (or less - the angle between the surface light falls on - i.e. pairs of opposed facets) and the RI. I can''t see how any diamond cut grading system can avoid that relation.

Thanks for the colorful citation


And one question, Garry: relative to the HCA chart, why do the other systems choose slots towards the right not left? Yield? Old habits? Are there diamonds being cut throughout the preferred HCA zone anyway?

 

[Garry H (Cut Nut)]

Date: 2/15/2006 7:51:17 PM
Author: valeria101

And one question, Garry: relative to the HCA chart, why do the other systems choose slots towards the right not left? Yield? Old habits? Are there diamonds being cut throughout the preferred HCA zone anyway?

Ana this is an edited quote from the G&G WLR article Fall 1998
The conspiracy theorists can see that big tables and deep pavilions are where the grading business lays (or is that lies).

http://www.gia.edu/pdfs/Fall_1998_Cut.pdf page 13 in the Box.

To get an idea of the range of WLR values for stones
seen in the diamond trade, we collected information
on the proportions of 67,621 round brilliants graded by
GIA GTL. (This data set included all the D-to-Z-color
round brilliant diamonds seen during a span of
months……..
More than 80% of this group of diamonds fell within
the smaller proportion range of 30°–40° crown angles,
40.2°–42.4° pavilion angles, and table sizes from 53%
to 70%. ……………………………….The stones with
average proportions for this sample set (represented by
29% of the sample) had crown angles between 31° and
35.9°, pavilion angles between 41.0° and 42.4°, and
table sizes of 61%–63%; ………….
7,617 diamonds had crown angles of
36° or more,……… There were 275 round brilliants
that had crown angles of 40° or more………
This sample of 67,621 diamonds contained very
few with proportions that would qualify for a top grade
in most of the systems shown in table 3. Only 3% of
the sample (2,051 round brilliants) had crown angles
between 34.0° and 34.9°, pavilion angles between 40.2°
and 41.3°, and table sizes between 53% and 57%.
............................................................nearly
twice as many diamonds had pavilion angles of
41°–41.3°, rather than 40.2°–40.9°. Thus, even manufacturers
who strive to cut “Ideal” proportions often
choose to cut a larger table or steeper pavilion angle
than Tolkowsky recommended, presumably for
greater weight retention.

 

[Garry H (Cut Nut)]

What if I put the GIA Excellent outline onto the HCA charts as I have done with AGS''s white outline?

Would that be educational?
HCA and GIA''s info are both free so it is not a commercial usage nor is it hindering GIA''s commercial interests.

I think I would not put the VG boundaries because that would be pushing the limits - and it would not be useful for most people here who are looking to be assured of buying a nice diamond.

Marty published the comparison charts already with GIA''s and AGS''s data - have not heard about lawyers letters?

Would it be useful?

 

[Regular Guy]

Garry, even if you allowed some indifference to the procedural and practical implications for the user of "mixing milk with meat," (not a kosher practice), I would hate to see you making yourself ill for the practice of aligning the data as you've suggested.

(Edited to add)...so, another approach, and one I've long thought would be available once GIA did make their proportion data available, has been demonstrated as viable by Scott, a recent poster here, who has engaged in some creative data mining to get what he wants, and virtually ignoring GIA's own categorization of cut quality. Although the effort you've suggested, Garry, has the promise of less drudgery by allowing inductive searching rather than deductive, your own questions concerning the goodness of the GIA categorization do raise concerns about this approach, don't they?

 

[JohnQuixote]

Date: 2/16/2006 6:04:14 AM
Author: Garry H (Cut Nut)

What if I put the GIA Excellent outline onto the HCA charts as I have done with AGS's white outline?

Would that be educational?

HCA and GIA's info are both free so it is not a commercial usage nor is it hindering GIA's commercial interests.

I think I would not put the VG boundaries because that would be pushing the limits - and it would not be useful for most people here who are looking to be assured of buying a nice diamond.

Marty published the comparison charts already with GIA's and AGS's data - have not heard about lawyers letters?

Would it be useful?

Speaking as one in the trade I’d like this as a curiosity - but Garry asked 'would it be educational?' So, would it help the uneducated or cause confusion?

Rounding: 60 57 34.8 40.9 (1.6 evve HCA) is forced to 60 57 35 41 (2.1 vvve HCA) on a GIA report. It’s possible a consumer could buy based on a HCA x-y coordinate, then feel confused or deceived as a result of forced rounding. It's explainable, but the explanation requires elaboration.

Steep/Deep: The overlay will indicate up to 41.8/34 as EX in some combos. I’m asserting my opinion here, but that’s outside many experts’ comfort zones for top make and I worry about it appearing as a top option for consumers.

Mixed message: The HCA favors shallow, but not adversely so. GIA’s steep/deep predilection is more damaging and, even if not reflected in the numerical result, I wonder if having it displayed would send a mixed message.

Brillianteering: There’s no way to account for GIA’s current position, so a consumer could again feel they have a GIA EX and later feel deceived if it were downgraded.

The beauty of the HCA is its simplicity. As simple as it is, explanations are already needed in its current form. Including disparate/contrary information could raise so many questions for new consumers that it may defeat the HCA’s most appealing aspects (simple and reliable). The HCA is already proven as a system. With respect, this new GIA system is not.

 

[valeria101]

Date: 2/16/2006 6:04:14 AM
Author: Garry H (Cut Nut)

What if I put the GIA Excellent outline onto the HCA charts as I have done with AGS''s white outline?

Would that be educational?
HCA and GIA''s info are both free so it is not a commercial usage nor is it hindering GIA''s commercial interests.

I would love that! If there is divergence of opinion (= CONTRADICTION) between different lab''s opinion of what is great or merely good, bad or ugly... one picture would make short work of the thousands and thousands of words wasted on the subject on now well buried threads.

One suggestion: instead of crowding the HCA chart, why not clean off even the existing AGS outline and make a full-screen chart with the overlay - for one or two table sizes, for starters. And since the matter (i.e. contradiction between lab''s value judgements) is an important one, there could be a little caption and a bit of reading linked below. For example, say this one page thing could be an item in the FAQ, the journal or tutorial, linked prominently under the HCA chart.

It may be an overly personal view, but the one thing I am trying to pass though with this is... is that the systems may not be as daunting to handle if their common background is emphasized. And a sloping line is not such a difficult concept

Even if so much sweat and cash are spent to research it.

 

[Garry H (Cut Nut)]

I thought I posted here - it must not have worked.

Thx everyone for advice.

I still feel the simple outline would be easiest for many people to understand.
Complex explanations from me are a bit like sour grapes - I said - they said....
You all can do that

I think I should procede to make the graphics

 

[Regular Guy]

So, perhaps, and at least in part, I''ve played (loudmouth, amateur) devil''s advocate, being as much a fan as JohnQ of the existing and simple HCA, but also, valuing the true point Ana was making:

Date: 2/16/2006 1:14:15 PM
Author: valeria101

Date: 2/16/2006 6:04:14 AM
Author: Garry H (Cut Nut)

What if I put the GIA Excellent outline onto the HCA charts as I have done with AGS''s white outline?

Would that be educational?
HCA and GIA''s info are both free so it is not a commercial usage nor is it hindering GIA''s commercial interests.

I would love that! If there is divergence of opinion (= CONTRADICTION) between different lab''s opinion of what is great or merely good, bad or ugly... one picture would make short work of the thousands and thousands of words wasted on the subject on now well buried threads.

Still, (and if you think this is important...you be the judge!) to help the user in taking care to not make assumptions about the implications of the association between placement of the cross hairs on the chart (the principle), and how that information will apply to any specific diamond the user has in their hand (the practical), a couple of suggestions about design might help, and Ana has made one above. Here''s another:

I now see that, with the current presentation of the cut advisor, you have users begin to walk through the tutorial after engaging in its use. Consider this, then. In the tutorial, lift out the first page on Grading reports, and place it into the Advanced Info section, and between the HCA page, and the page on AGS Ideal Cuts. Then, update the page on grading reports, as you see fit, such that you can provide any procedural warnings that you might seem and deem as appropriate and necessary. For example, from my reading here, two observations come forward:

- Re GIA data, though not sure I understand it all, the rounding thing, it seems to me, has implications for just understanding what the actual proportions are on the diamond. This place on the tutorial would be a helpful (and as Ana says, good and simple place to have this sort of info all in one place, since RockDoc points out it is not otherwise on the cert) spot to iterate it out.
- re AGS data, users could understand their diamond will in some instances be regarded as AGS0 for light performance, even if the cross hairs are out of whack, as a result of briallianteering, and this could be reviewed here. Unless you think it is advanced advanced, the concept of brialianteering altogether could be reviewed in such a spot as well, unless it is more tempest in a teapot

Final point about this...my suggestion goes towards a more simple reordering of info already presented otherwise to help explain the new data you''re proposing being presented. All actions have consequences, of course. Adding the new comparative data, as your idea suggests, has both upsides, for the added info, but implications in presenting it. The implications goes towards wanting the reader to have a context into which the new info might most usefully be placed. You have probably felt comfortable, without much further ado, to overlay the AGS0 template on the existing HCA graphic, because of the respect afforded their criteria. Consider then, perhaps adding one more slide (?), which will not only give the facts, mam (reviewed above), but also which steps aside, and does some more comparative discussions, and may take up some of the possibly more nuanced points we read here, such as:

- judgements GIA has made based on a poor choice of color trays?
- judgements about brillianteering (i.e., digging, cheating, etc.) that each agency has made
- procedural dynamics that go into the placement of a grade that will respectively provide a benefit or detriment to the goodness of the grade (if GIA principally uses now proportions, vs AGS to also consider observations of light performance, this could be usefully noted)
- regarding rounding, and reflecting on the numerical data now displayed on the grading chart...though no one has talked about this that I am aware of, what is being described about rounding for GIA is something you have pointed to about EGL for a long time, causing you to encourage the use of angles vs percents, and also, causing AGS to be squished into a tiny spot for those who do not use rounding?)

Anyway, just some more grist for the mill. Thanks again for asking, and not to mention, the necessary elbow grease to make this all come together.

Regards,

 

[JohnQuixote]

I''m inclined towards Ana/Ira''s suggestions if you''re going to do it Garry. It sounds like you want to. Being on the receiving end of questions generated by the HCA I''d like to note that, simple as it is, some follow up is still necessary in its present form. Ana''s "Labs would grade this differently (click here)" idea is promising, and I believe Ira and others have contributed to iterations of the text used. It''s a great tool and I''m confident you''ll be able to keep it robust.

As I write this it occurs to ask; Would it be helpful for a few dealers to compile the most FAQ we encounter from clients who bring up the HCA and IS?

 

[valeria101]

Date: 2/17/2006 10:37:47 AM
Author: JohnQuixote

As I write this it occurs to ask; Would it be helpful for a few dealers to compile the most FAQ we encounter from clients who bring up the HCA and IS?

If ''yes'', then there is a hoard of that sort of material on Pricescope too

 

[Garry H (Cut Nut)]

thx Ira, John and Ana,

on a trip - will get back to this later

 

[valeria101]

Someone turned in a new GIA cert in a post today...

... would this be a fair interpretation of the numbers ?