Girdle Question

John

__________________________

John Pollard

Whiteflash Director of Education 2004-2007

Ideal-scope images below:  Traditional brillianteering (left), painting (right).

Capable cutters would point out that the minimal-leakage footprint on the right is not a definite sign of painting:  There are other ways of running a stone that will acquire such a look in a reflector.

My observations below are specific to diamonds with good optical symmetry, which behave differently than those without.  Others can comment on painted or dug diamonds cut purely for weight retention, not optical symmetry (we don't see many of those on PS).

When there is spread in the angular relationships (associated with traditional brillianteering), light returning to the viewer’s eye is splintered along symmetrical paths and junctions at different angles, giving an intense, on-off look to the scintillation.  In diamonds with balanced major and minor configurations the sharper dispersion is beautiful in all illumination scenarios, with small pinpoint flashes that are especially intense in bright light conditions.

When the angular relationships of the facets are closer (associated with painting), light return flows easily across the closely matched angles.  In diamonds with balanced major and minor configurations this creates large, broadfire scintillation, described as fluid and colorful.  The  spectral colors are especially notable in soft light conditions like candlelight, when your pupils are dilated.

John

__________________________

John Pollard

Whiteflash Director of Education 2004-2007

David S. Atlas

GG(GIA), ASG, Sr. Mbr. NAJA

www.datlas.com

John

__________________________

John Pollard

Whiteflash Director of Education 2004-2007

John

__________________________

John Pollard

Whiteflash Director of Education 2004-2007

Date: 3/13/2006 3:27:11 PM
Author: Lynn B

Thanks, John. Appreciate the detailed information.

Feeling a bit ashamed to admit this but still wondering... is this, then, (likely) a painted girdle?

(It's the IS of my stone. 2.36 AGS-0, 55, 60.5, 34.4, 40.8)

John

__________________________

John Pollard

Whiteflash Director of Education 2004-2007

Date: 3/13/2006 9:55:01 PM
Author: Lynn B
And John, TOTALLY off-topic, but how in the world do you quote two different 'authors' (me and Dave) in ONE post, like you did above? Apparently I am either Quote-Challenged or living in Quote Purgatory because I am having a terrible time!!!!

Thanks!
Lynn

John

__________________________

John Pollard

Whiteflash Director of Education 2004-2007

I'm seeing this as well.

These approaches have been around for generations.  Digging and painting are just words.  They are parts of the manufacturing process, like cleaving, sawing, blocking, etc.  They are not common parlance when discussing diamonds in the mainstream:  If you drop these terms there are many jewelers and appraisers who won’t even know what you’re talking about.  They are nothing to fear.  Poor brillianteering will result in an inconsistent, wavy or knife-edge girdle, which will be downgraded by reputable labs.

A lot of buzz (and worry) has been created on the forum lately.  Here is a simple overview.

With the vast majority of diamonds:

The thickness of the girdle is marked at blocking, and revisited before brillianteering.  As the polisher puts the facets on he meets those marks.  He may dig a bit or he may paint, depending on the desired yield and girdle thickness.  It is all very natural.  The approach is like choosing a fork or a spoon, according to the dessert you’re eating.  The intent is to finish the diamond beautifully, particularly in premium makes (often seen on PS) where utmost care is taken throughout the process.

In extreme cases:

The main reason for extreme digging is because a stone may be steep/deep and there is a need to make that stone appear to have a medium or thin girdle.  Remember, the desired girdle thickness is marked.  By digging the upper and lower halves, starting from the girdle out toward the poles, thinning of the girdle occurs and the cutter meets the mark.  This tends to hide weight.  Digging may also be referred to as gouging.

In the case of shallow diamonds (where the girdle is marked to be quite thin), the cutter may need to start from the poles and polish toward the girdle to preserve the marks and avoid thinning the girdle any more.  This is painting.  If too much material is taken away it could result in a knife-edge girdle.

Of the two, digging is far more deleterious than painting.  It can hide weight and reduce performance.

The ‘buzz’ lately is because GIA has decided to downgrade a certain level of digging or painting without analyzing the actual diamond.  This is positive for average consumers in common situations (like the mall) as they will be protected from gouging for the purpose of saving weight…  Unfortunately, a small baby was thrown out with their bath water:  A few brands of the most carefully finished premium diamonds are painted on purpose.  Coupled with optical symmetry, this technique can result in some of the most spectacular diamonds in the world.  Unfortunately, along with such shortcuts as rounding of numbers, GIA is lumping that tiny percentage of wonderful premium makes in with the larger percentage of ‘save the weight’ cases.

With premium optical symmetry, like we often see on Pricescope, beauty was always the objective.  It was not about saving weight.  If the girdle is consistent and the painting was deliberately designed to beautify (as with Lynn’s diamond) it should not be downgraded.

Hope this helps.

John

__________________________

John Pollard

Whiteflash Director of Education 2004-2007