Question about grading cut

[pyramid]

QUOTE: 2.01cts. Thin Girdle 10X EGL/LA
"A nicely bruted girdle shows two areas where the girdle thickness becomes rather thin. Since thickness is graded at the midpoint between the facet junctions, here it is slightly greater than the actual thinnest portion of the girdle.
If it were graded at the thinnest section of the girdle only, the grade would be Very Thin".




Why is the girdle not graded at the thinnest section only?

 

[oldminer]

My own labs grades girdle thickness at the extremes. We look at the thinnest and the thckest portions, not somewhere in the middle. My gosh, if one was trying to use an "average thickness" in order to report min and max, how dumb would that be? I suppose there is always a new way to do a job half a**ed.

Every lab has the right to have their own procedures, but common sense tells you that something is not right if reporting minimum and maximum is based on other factors.

 

[pyramid]

Thanks oldminer. I wondered if it was something to do with the body of the diamond being narrower at the valley rather than at the halves which was where that picture showed the very thin girdle?

 

[oldminer]

To me, if a girdle is thick overall and yet very thin somewhere, it is exactly that (very thin) as a minimum. No other logical explanation could exist. Surely, illogical explanations make what I said sound like I am an unreasonable lunatic. If someone has a different explanation that truly makes my logic wrong, then I'd be glad to read and further my own knowledge, too. I don't mind finding out I don't know it all. Just try not to make it too painful, please. Thanks. TGIF

 

[pyramid]

Thanks Oldminer. I''m sure you are not in the field you are in without knowing most of it.

 

[pyramid]

Does anyone else have an opinion about why a lab would grade in one position on a stone when other positions could have a very thin or extremely thin girdle?

Does anyone know why labs grade at different positions instead of thinnest and thickest parts of the stone?

 

[Richard Sherwood]

From what you report Pyramid, it appears that the EGL lab is using only the midpoint girdle position for their "official" girdle thickness, while making a notation if another portion of the girdle is thinner (or thicker) than this.

It''s a little strange, but as long as they report if another portion of the girdle varies from the reading taken at the midpoint section I guess it''s okay. The GIA lab, and most other labs I am aware of use the thickest and thinnest portions in determining their measurements, whether at midpoint or not.

 

[Richard Sherwood]

One reason they may be doing it that way is to show if there's something "out of the norm" with the girdle.

In other words, with a normal girdle the thinnest portion would always be at the midpoint between facets. If you have a girdle which is thinner somewhere other than the midpoints, then there would be some unusual factor creating this, such as an inclined natural on the girdle surface, or poor fashioning.

 

[pyramid]

The picture was in Gary Roskins book page 77.

It does not say there is a natural it just looks like the girdle below the very thin girdle is sloped out or slope in towards the very thin girdle. There is nothing below the girdle area. The sloping girdle just looks like the rest of the diamond and is polished. It is at the girdle halves.

They do not say that this is reported just as I typed that if the girdle was measured in this area the grade would be very thin.

As you say maybe it is just being used as an example for the book and the actual diamond would have had a minimum and maximum girdle thickness recorded on the grading report.

 

[pyramid]

Date: 7/10/2005 9:44:49 AM
Author: Richard Sherwood
One reason they may be doing it that way is to show if there''s something ''out of the norm'' with the girdle.

In other words, with a normal girdle the thinnest portion would always be at the midpoint between facets. If you have a girdle which is thinner somewhere other than the midpoints, then there would be some unusual factor creating this, such as an inclined natural on the girdle surface, or poor fashioning.

above such as an inclined natural on the girdle surface - how ''inclined'' does a natural have to be before it affects the girdle width?

 

[Richard Sherwood]

Date: 7/10/2005 7:36:55 PM
Author: Pyramid

Date: 7/10/2005 9:44:49 AM

Author: Richard Sherwood

One reason they may be doing it that way is to show if there''s something ''out of the norm'' with the girdle.


In other words, with a normal girdle the thinnest portion would always be at the midpoint between facets. If you have a girdle which is thinner somewhere other than the midpoints, then there would be some unusual factor creating this, such as an inclined natural on the girdle surface, or poor fashioning.

above such as an inclined natural on the girdle surface - how ''inclined'' does a natural have to be before it affects the girdle width?

About 10 degrees or more is usually enough to reduce the effective girdle width.

 

[Garry H (Cut Nut)]

Pyramid read Peter Yantzers article on girdle Indexing in the journal (lower left front page).

Also note that AGS have now changed from measuring the thin part (like GIA) to international standard of measuring at the thick part because that is where most other fancy shapes are measured.

AGs now allow (maybe even ecourage) thicker girdles which I think makes sense give our irrational fear of diamond chipping / breakage.
But their system penalizes smaller spread - so there is a

balance

 

[pyramid]

Thanks Richard Sherwood and Garry H.