question about depth

[nycguy]

i was under the assumption that if you added up the % of crown, pavillion & girdle it should equal whatever number the total depth is. after looking at stats for stones, i see this is not always the case. is there something i''m missing?

for example, if total depth is 60, and crown is 14% and pavillion is 43% and girdle is thin (around 1%), that only equals 58% - where does the other 2% go?

 

[adamas]

thats too much variance. The girdle is not even in round stones, that's why you get, thin-med, med.to sl. thick etc. but 2% is too much. It is possible that the stone has a variable girdle, thick on one side, thin on the other. or the table is not parallel to the girdle plain. Even with these explanations 2% is too much. Are you sure it's not 0.2% which would be in line.

 

[Paul-Antwerp]

I fully disagree with the previous reply.

Your question is a classical one, and it must have been answered a dozen times in other posts.

The American labs measure the girdle in the valleys, where they are the thinnest, while they measure crown height and pavillion depth on another spot. That is why the summation does not add up.

If you take the measurements of the Belgian HRD-lab, for instance, you will see that they do add up, because this lab takes all measurements at the same spot. The difference between the two systems is on average about 1.7%

To sum it up: this difference does not mean that anything is wrong with your stone, it is perfectly normal.

However, some untrustworthy people in the trade use this apparent inconsistency to cheat or mis-inform the public. If you do a search here on 'warped diamonds', you will find examples of this.

Live long,

Paul

 

[nycguy]

so are you saying that pavillion % + crown % + girdle thickness should exactly equal depth percentage?

the numbers i gave here only an example - but i've noticed when looking at alot of diamond stats that it seems that often the three numbers gives (crown, pavillion, and girdle) do not exactly add up to the depth percentage and i wanted to know if this was to be expected, or whether they should all exactly add up.

thanks.

 

[aljdewey]

Paul.....an excellent reply! Thanks for the reminder on this!

 

[nycguy]

thanks so much - that makes a lot more sense.

so, if a gia cert says the girdle is medium to slightly thick, what % is that approxiamately? (and i assume that according to your email, whatever this percenatge is it reflects the valley)?

gratis.

 

[adamas]

I'm thinking on a stone described a "thin girdle" 1%
Pauls explanation does not work for a 2% variance in total depth. A 2% variance would need to be knife edge to thick, best benifit of doubt would be a sl. thick.
All of my experience has the plane at the low's yes.
In this case the provided information is a 1% girdle with 2% missing. Correct me if i'm missing something but that would be a 3% girdle, based on the above answer. Must be a 10ct plus for 3% to be thin. To my though on large goods % goes out the window for girdle and rather were looking for 1.75mm. So I guess this means i'm disagreeing with Pauls explanation while trying to address the original question.

 

[pricescope]

nycguy:

----------------
so, if a gia cert says the girdle is medium to slightly thick, what % is that approxiamately? (and i assume that according to your email, whatever this percenatge is it reflects the valley)?

gratis.
----------------

According to Marty Haske, GIA measures girdle in mm. See http://www.gis.net/~adamas/cut.html#girdle

Thin: Less than 0.15 millimeters
Medium: between 0.15 and 0.20 millimeters
Slightly Thick: between 0.20 and 0.23 millimeters
Thick: between 0.23 and 0.33 millimeters
Very Thick: between 0.33 and 0.40 millimeters
Extremely Thick: greater than 0.40 millimeters

What are the measurements of your stone in mm?

Paul described the problem with AGS method of girdle measurements.

Besides crown and pavilion depth measured can have certain measurement error depending on the model. I think you shouldn't worry about 1%-2% difference.

 

[nycguy]

I think the problem was my example was just that - an example - not an actual stone from memory, but rather, an example based on the fact that i've seen many, many, many stats for stones that i notice don't add up. so it was just a general question, and i gave the example with numbers so to make my question clearer, but i think i just ended up confusing things.

anyway, i totally understand both of your answers now.

thanks.