Bob’s Flashes - Girdle Thickness – how important is it?

[dimonbob]

Bob’s Flashes - Girdle Thickness – how important is it? What does faceted girdle mean?

I have received several e-mails from customers with questions regarding girdle thickness.

The girdle is the outside parameter or rim of the diamond which separates the top (crown) from the bottom (pavilion), and is the area where the prongs or the bezel hold the diamond in place in the jewelry piece.

The thickness should not be too thin or too thick which means an ideal thickness would be thin, medium or slightly thick or any combination of these.

An extremely thin girdle would be a girdle so thin that it would be knife edge sharp. If the complete girdle was extremely thin, that would be an accident waiting to happen. In most cases only a very small area of the diamond girdle is extremely thin. If that portion of the girdle that is extremely thin receives a sharp knock it may chip. If you find a diamond that has a girdle range that includes extremely thin, be sure to work with a vendor that can eye ball the diamond and let you know if it poses a problem or not.

If the girdle is too thick as in extremely thick, there would be too much weight of the diamond in the girdle and the diameter of the diamond would smaller than the same weight diamond with a medium girdle. In other words the diamond would appear smaller. An example; if a diamond with a 6.6mm diameter and a 60% depth with a very thin girdle it will weigh about 1.08ct. If it has a very thick girdle it will weigh about 1.18ct. If the girdle thickness is extremely thin and extremely thick the difference will be greater.

The girdle of a well cut diamond is not a constant thickness but fluctuates slightly. That is not to say that it is wavy. A wavy girdle can be observed by looking at the diamond from the side and the girdle appears to wave up and down. The girdle should appear as a straight line that slightly fluctuates in thickness.

Up until about 25 years ago almost all round brilliant cut diamonds had what is called a bruted girdle. It is slightly frosted in appearance and is made from one diamond being held against another diamond that is turning at a fairly high rate of speed in a lath type machine. The diamond is rounded up in this way. If the person doing this operation has a heavy hand this process leaves many hairline feathers extending into the girdle. This is noted as bearding on the Diamond Grading Report.

Many diamonds on the market have bruted girdles and many of them are beautiful with no bearding whatsoever. This is fine. An AGS Ideal cut can have a bearded girdle.

Another type of girdle is a faceted girdle. Instead of a frosted appearance, this girdle has tiny facets around the girdle that have the same appearance as any other facets on a diamond. They are clear and polished. Faceting and polishing takes out any hairline fractures that may have been a result of the rounding up process. It leaves a fresh clean appearance and is preferred by many diamond enthusiasts. The same rules apply to a faceted girdle as to an unfaceted girdle with regards to thickness.

 

[Lynn B]

Bob,

Thank you very much for...

Everything I Ever Wanted To Know About Girdles*

* but was afraid to ask!

Seriously, it was very interesting and informative. Thank you for sharing.

Lynn

 

[researcher]

I think this info is EXTREMELY helpful, but I don't understand why you would want a girdle that varies. Why isn't it better to have a girdle that is consistent? Is this different for different shapes? I'm just curious because several sources for princess stones have stated that a girdle without variation is best because the various facets line up better.

 

[DiamondExpert]

Researcher -

I think what Bob is referring to is the small variations in girdle thickness (like in this round example - sorry for the inscription, but was only one I could find quickly) resulting from the different angles of the different groups of facets...e.g., upper/lower girdle vs. upper and lower mains.

 

[researcher]

Okay, that makes sense I was just confused trying to figure out how a TN-STK girdle was possibly better than a medium girdle! Sometimes I'm just not thinking! LOL

 

[Judi W]

and we thought a girdle was something women USED TO WEAR and happily - do not any longer!!!!

Sorry DiamonBob....couln't resist!

 

[alexah]

Thanks diamonbob - interesting read.

I also wonder about what researcher asked - "Why isn't it better to have a girdle that is consistent? Is this different for different shapes?"

I have a princess cut & went out of my way to look for a medium polished girdle - I heard that, in lower near colorless stones, faceting of the girdle will reflect more color back to the eye so a consistant girdle's best. Anyone: True or False?

Thanks!

 

[dimonbob]

Theoretically it would be ideal to have a thin or a medium girdle but we are talking about very very small numbers and in actualuality NO ONE can see the difference. It is just like me a my D color obsession. I want a D color diamond but I know for a fact that I cannot see the difference in a D and an E in a set ring.

Sometimes we get caught up in the tiny details that do not amount to a hill of beans.

To me a perfect diamond would be a 5ct D Flawless ACA with a thin or medium girdle and a HCA of 0.8! How much of this really counts? Would a 4.75ct E VS1 ACA with a thin to slightly thick girdle and a HCA of 1.8 look the same. Yes, exactly the same! It would also cost a lot less!

Details. We need to be a little more flexible. There is not much in this world that is perfect.

 

[squirerad]

Does the thickness or thinness of a girdle adversely affect brilliance, fire, scintillation?


squire

 

[DiamondExpert]

squire - I think between a Thin to Slightly Thick girdle - No. When you get to extremes, however, it could possibly be another story.

Perhaps more important is whether the girdle is faceted or bruted...Like Bob, I have personal "hang ups" about stones and having a faceted girdle is one of them - it just looks nicer, and probably won't collect dirt/metal/etc. and become gray as easily as a bruted girdle - it will also be easier to clean.

Personally, I also have strong preferences for rounds concerning color (D or E), clarity (nothing below a VS1), cut (thin-med girdle, X/X, 54-56 table, 60.3-61.0 depth,pavilion depth 42.6-43.0, 34.2-34.6 crown angle, 40.6-40.7 pavilion angle, etc.), but these are personal and for the most part cannot be seen with the naked eye. These irrational, and severe restrictions should not be considered by individuals looking to purchse a diamond because they would miss a great many great looking stones. I'm a great proponent of letting your eyes dictate what suits you best.

 

[Garry H (Cut Nut)]

Great work Bob

But what would be you GIA preference for girlde thickness on your 5 ct stone?
An AGS thin would be a GIA thick, and a gIA thin would be an AGS very thin or maybe even extremely thin.

Folks the GIA more or less measures the girdle thickness and so as the stone gets bigger the thickness % reduces for the same grade.
GIA and AGS measure the girdle thickness at the thinnest point - the 'valley', while European based labs measure at the main or bezel facets. A European lab's pavilion, crown and girdle thickness add up to the total depth %, where-as all US labs graded diamonds are warped (he he he).

 

[luvmysparklies]

Hey, that's a great read! My question is something that I've been curious about for a while. Why does a thicker girdle ADD weight? It would seem like to make a thick or extremely thick girdle the cutter would wear away at the diamond material, making the circumference (or diameter) smaller. So with the diamond material being worn away in making the girdle thick/extremely thick, why would it weigh more? Thanks again, this was a helpful amount of information. Bob, please "flash me" again!

Luv

 

[fire&ice]

----------------
On 6/14/2004 8:28:37 AM luvmysparklies wrote:

Hey, that's a great read! Why does a thicker girdle ADD weight? Luv----------------

Yes, this is a very good read. I even bookmarked it.

That said, in layman's terms - the girdle has weight retention. It's holding weight in an area that isn't visable face up. So, it will appear smaller; but possibly weigh more. Just like people - it's the way the weight is distributed as to what one appears to be in size (this also goes to issue of depth %). You may have two people who weigh 120 whose appears of size is completely different.

 

[glitterata]

Luv,

The answer is that when you wear away the girdle, you're removing length from the diameter--you're making the stone fit into a smaller circle. So even though it weighs less than it did before you wore away the girdle, it weighs more than a stone of the same (new, small) diameter, but with a thinner girdle.

One way to think of it is to imagine taking a stone with a thin girdle, slicing it through the girdle (separating the crown and pavilion), adding a circular disk of diamond between the two slices, and then magically fusing it back together. You'd have a diamond with the same diameter, but a thicker girdle--and it would be heavier than before by the weight of the disk that you added.

Does that make sense?

Basically, you have to compare the weight of two stones OF THE SAME DIAMETER but different girdle thicknesses.

 

[luvmysparklies]

Alright, now I understand the context of the expression "added weight" in a thick girdle. I actually already understood that a thick girdled diamond will not appear to be the weight that it should be since its circumference (diameter) is smaller than it should be-- and that other diamonds with the same diameter that are properly cut weigh what they should weigh. I guess what confused me was the term "added weight", like the girdle somehow made the stone heavier. But, thanks for the clarification gang! It helped me to understand the context of what terms mean

Luv