Girdle thickness: terminology and suggestions

[oldminer]

You often see the girdle thickness of a diamond as a single word description such as “medium” or “thin”. Many diamonds do have reasonably consistent girdle thicknesses, but when they don’t using a one word description can be misleading to truly dangerous for the consumer. Below is a list of all the possible combinations of words to describe girdle thicknesses. There are 45 potential combinations.

Med
Thk
Thn
Slthn
Slthk
Vthn
Vthk
Xthn
Xthk
Xthn-Xthk
Vthn-Xthk
Thn-Xthk
Slthn-Xthk
Med-Xthk
Slthk-Xthk
Thk-Xthk
Vthk-Xthk
Xthn-Vthk
Vthn-Vthk
Thn-Vthk
Slthn-Vthk
Med-Vthk
Slthk-Vthk
Thk-Vthk
Xthn-Thk
Vthn-Thk
Thn-Thk
Slthn-Thk
Med-Thk
Slthk-Thk
Xthn-Slthk
Vthn-Slthk
Thn-Slthk
Slthn-Slthk
Med-Slthk
Xthn-Med
Vthn-Med
Thn-Med
Slthn-Med
Xthn-Slthn
Vthn-Slthn
Thn-Slthn
Xthn-Thn
Vthn-Thn

Xthn-Vthn

Another issue is the use of the word “Average” when it comes to the girdle thickness of a diamond. If you have a diamond with Xthn to Xthk ranges, the “average” the industry often then uses is “Medium” to describe the girdle in a single word. Who benefits from this is pretty obvious. In fact, the diamond may have mostly Xthn or Vthn girdle with only a tiny spot of the opposite thickness. Then it isn’t even a matter of a medium thickness girdle being found anywhere on the stone.

When an “average” is taken from measuring 8 or 16 places on the diamond it all makes more sense, but using the mid-range between two extremes can be dead wrong. Really, the right terminology should be “Mode” for the one word used when 8 or 16 measures are taken. The most common measure is probably a better indicator than the potentially non-existent range implied by using “Average”. At least a “Mode” terminology would be some proper indicator of the overall cut of the diamond and a proper use of the words themselves.

Food for thought late on Friday before a long weekend.......

 

[Lorelei]

Definitely food for thought and well worth bringing this up, thank you Dave!

 

[oldmancoyote]

The old quip "A person with feet in the oven and head in the freezer can be described as ''comfortable, on average'' ".

Mode or median would definitely be better than range for anything that is measured across many points - not just girdle: think pavillion and crown angles...

 

[Diamond Explorer]

Certain features of the diamond, such as a natural on the girdle though can also complicate things too. Lets say the average or modal thickness is medium or slightly thick. A natural could make the girdle extremely thin in one part without sacrificing the durability. But GIA would still say the girdle is extremely thin to slightly thick. This could be a beautifully proportioned and durable stone yet the GIA report would still read extremely thin! This would be one feature of a diamond that you really cant read from the report. Thanks for your post Old Miner. Definitely got me thinking!

 

[Garry H (Cut Nut)]

Hi Dave,
What a great topic and interesting number.

And just for fun every lab has a different boundary and a different method or place to measure - valleys, main junctions etc.
GIA examines and does it by eye, AGS uses %, AGS thin on a 100ct stone is thick enough to write your name on, GIA''s is the same thickness as on a 1/2ct.....and so it goes...............

 

[strmrdr]

While interesting I don''t see it as a huge issue.
Buy from someone who actually looks at the diamond and is honest enough not to sell a problematic stone and don''t worry about it.
Or if you buy from a drop shipper use an appraiser within the return period.

 

[kcoursolle]

My personal thought is that they should just put the percentage like they do with depth and table. It''s more meaningful and most consumers don''t learn "thin, thick, etc." or even what a girdle is anyways, so for the people who want to know a percentage can tell you more information and they can learn for themselves what percentages to look for.

 

[Diamond Explorer]

Date: 4/5/2009 2:55:14 AM
Author: kcoursolle
My personal thought is that they should just put the percentage like they do with depth and table. It''s more meaningful and most consumers don''t learn ''thin, thick, etc.'' or even what a girdle is anyways, so for the people who want to know a percentage can tell you more information and they can learn for themselves what percentages to look for.

I agree, that would be the easiest to understand across the board, but you still have the dilemma of what value to use, as the measurement areas and averaging methods still vary from system to system.

The labs should be more consistent universally with their nomenclature and methodologies. That would make it easier to compare diamonds across systems.

 

[Serg]

what is girdle thickness for Cushion cuts?
If girdle facets will have 5-10 degree slope( conical girdle), what is it girdle thickness in such case.
I think current approach is wrong and misleading fo consumer. For consumer is more important:
1) Durability
2) Spread

These two criteria is much more important and clear for consumer than a lot of gradations for girdle thickness with quite "strange" definitions even for RBC( valley, bone, bezel)

Fancy cuts have troubles to use such ''definitions ''
I think industry should change approach, do it more consumer helpful and user-friendly

 

[Paul-Antwerp]

You are absolutely right, Sergey.

 

[oldminer]

ALong with ImaGem I developed a Durability - Finish - Size set of parameters and a consistent way of applying them to all shapes. It is the DFS system which ImaGem will be marketing as part of their Diamond Essence program. The average girdle measure it uses is based on many readings of girdle thickness all around the diamond, not on min-max.

The mention of slightly sloped lower girdle facets on some shapes such as cushions are highly interesting to understand. In this way the cutters retain huge weight benefits and escape the Very Thick or Extremely Thick girdle comments from the labs. This is indeed a huge shortcoming of how things are being done by the labs all of us trust. I am sure I''ve seen a few cushion cuts where 35% of the depth would have been girdle had the lower girdle facets been vertical instead of ever so slightly angled inward...... Just one more bit of the game of diamonds.

I think the AGS 0 princess cut has a mid-pavilion break angle which serves to add some weight retention, but it is not nearly as extreme as some of the cushion shapes I''ve seen. Maybe Paul would comment.

 

[diagem]

Date: 4/5/2009 5:32:21 AM
Author: Serg

what is girdle thickness for Cushion cuts?
If girdle facets will have 5-10 degree slope( conical girdle), what is it girdle thickness in such case.
I think current approach is wrong and misleading fo consumer. For consumer is more important:
1) Durability
2) Spread

These two criteria is much more important and clear for consumer than a lot of gradations for girdle thickness with quite ''strange'' definitions even for RBC( valley, bone, bezel)

Fancy cuts have troubles to use such ''definitions ''
I think industry should change approach, do it more consumer helpful and user-friendly

Yep...

I believe based on my experience most straight edge girdle planes are conical shaped..., which could very well be a durability issue..., (especially if sloped towards the pavilion.)