Another question about GIA cut grading....

[togal]

My stone was recently graded by Gem Scan, which is the largest gem grading and appraisal lab in Canada (an ISO registered co.), and on the back of the grading report it states that "The grading terms in the report are based on GIA standards". However, when I look at the GIA cut table, my stone rates an "Excellent" cut grade, but Gem Scan gave it a "Very Good" cut grade. I know, as many, including myself, have said before, other than the price paid for the stone, the words "Excellent", "Very Good", etc. don't really matter, as long as one is happy with their purchase. But it really makes me wonder why, if Gem Scan uses GIA standards, then shouldn't the cut grades match-up? The grader at Gem Scan told me that the table size caused the "Very Good" rating. What gives?

Does this mean I got a bargain?

The specs on the RB stone are as follows:

Depth: 61.8

Crown: 35.2 degrees

Pavillion: 41 degrees

Table: 58.9%

Girdle: Medium

Culet: V. Small

 

[belle]

you are probably looking at the chart using a 41 degree pavilion angle. what you have is a 41% pavilion depth. a 41% depth would equate with a lower pavilion angle on the chart. coupled with the 35.2 crown, you would miss the ''excellent'' grade using both the 58.9% table as well as the 59%.

 

[togal]

Hi Belle,

No, the pavillion depth is 44% -- the pavillion angle is 41 degrees. My crown depth is 14% -- 35.20 degrees

 

[belle]

well...i tried to make sense of it!

i''ll go back to doing what i''m supposed to now...

 

[togal]

Hey, thanks for trying Belle......maybe someone esle can chime in.

Now I also need to get back to what I''m supposed to be doing!

 

[Rhino]

Hi Togal

Belle is to be thanked for trying.

Her heart is in the right place.

I happen to be familiar with GemScan lab reports since we do have stones shipped from Canada from time to time so let me explain.

GemScan only lists on their reports the polish and symmetry gradings so the "very good" you are seeing (to my knowledge of this) is strictly polish and symmetry grading and not an overall cut grade. In the GIA Ex cut grade polish and symmetry gradings of "very good" are acceptable and just fine since polish and symmetry have the least impact on optical performance which is primarily dependant upon your proportion combinations. (Note: There are however lighting conditions that do indeed flatter precise optical symmetry but neither GIA or AGS grade for that).

So in short ... as long as the polish and symmetry are indeed "very good" as GemScan states (and in Canada they enjoy a good reputation from what I know) you do indeed have a stone that would qualify as a GIA Excellent cut grade, provided that

a. the culet is no bigger than medium,
b. the girdle thickness is not less than "thin" or no thicker than "slightly thick"
c. that the upper and/or lower girdle facets are not painted or dug out
d. also ... it really helps to know the lower girdle facet and star length to be 110% sure as these are factors GIA looks at as well but a good majority of stones on the market do fall within their specs for this.

Of course the best way to confirm all of this would be to have a knowledgeable appraiser who is familiar with the GIA cut grading system to do a full inspection on it who can provide this detailed data. So far with what you have provided though it looks good.

Hope this helps.

Kind regards,

 

[togal]

Hi Rhino,

Once again, thanks for your reply. What a great source of information you are.

I did get an insurance appraisal from Gem Scan, in addition to the more detailed report that listed the degrees & percentages, etc. The appraisal does list "Cut" as Very Good, so I assumed that meant the overall cut grade (not just polish and symmetry)....but I could be wrong.

Well, I know that:

A) The culet is - V. Small
B) The girdle thickness is - Medium
C) Don''t know about painted or dug out girdle facets (not exactly sure what that means, but it doesn''t sound so good

)
d) Don''t know about the lower girdle facet or star length either (first I''ve heard of this

)

Well, I am very happy with my stone and glad that it charted as Excellent on the GIA table....for whatever it''s worth!

Thanks, and have a great weekend...