Dug Out Girdles

    In most of the diamonds we have analyzed to date that exhibit "digging", we have generally found it to be amongst the upper girdle (also referred to as upper half) facets which are angled further away from it's neighboring main facet and more towards each other causing a steeper angle in the half facet as a result.  To quote GIA; "...the half facets can be fashioned so that they lean toward each other, thereby creating steeper angles between each upper or lower girdle facet and its neighboring bezel or pavilion main facet, and steeper angles of the halves themselves with respect to the horizontal (in which case they are referred to as “dug out” facets). These techniques are well known in the diamond cutting industry, but seldom discussed outside of that group."

    If that was a little tough to understand, the graphics below will help you to better grasp the concept and what it is that is being looked at. The diamond used in this example is one that just falls outside of the AGS Ideal range and will be submitted in January to see how it qualifies on the new GIA Cut System (we don't anticipate Excellent grade).  Below is a look at the first piece of data and the first graphic is of a stone with dug out upper girdle facets next to the classic ideal girdle.  Note how the girdle thickness from bezel to half is not consistent as it gets thinner at the half.

Here's a zoomed in view of this comparison.  It's easy to see how the girdle thickness at the halves (bone) are thinner and not consistent like the classic girdle.

Classic Girdlel
Dug Out Girdle

The girdle graph as generated from a Helium scan on this diamond shows us this.  The graph shows the obvious difference with the girdle half facets at the crown being pushed down not maintaining even thickness around the diameter of the stone.

Classic Girdle
Dug Out Girdle

When we compare girdle measurements via Sarin we can note this difference numerically.  Note now the difference between the girdle thickness at the bezels as compared to the girdle thickness at the halves.

Here is side by side next to the ideal classic girdle.  Note the difference in girdle thickness between the halves and bezels among these 2 stones.  Also take note of the upper girdle and lower girdle angle relationship.  On the Classic Girdle we have a 42/42 relationship while the diamond with the dug out girdle has steeper upper girdle angles (45.3°).  This is what GIA was referring to when they state "the half facets can be fashioned so that they lean toward each other, thereby creating steeper angles between each upper or lower girdle facet and its neighboring bezel or pavilion main facet, and steeper angles of the halves themselves with respect to the horizontal (in which case they are referred to as “dug out” facets)."

Classic Girdle	Dug Out Girdle

Accurately taken Red Reflector images also demonstrate a difference from the classic ideal girdle. (Note: Not all reflector photography taken reveals this so we recommend examining Sarin/Helium details first and foremost).  The thing to take note of here are the fainter and more pale reds in the upper girdle region.

Classic Girdle	Dug Out Girdle

ASET images make an even sharper distinction.  These ASET images are generated from Helium scans (arguably the most accurate scanner in the world, especially for the purpose of model creation) and emphasize a rather obvious difference.  The concentration of green around the upper girdle region tell us that this diamond is drawing a lot of light from the hemisphere (0-45° angles).  If you've read through our article on "What the Reflectors Teach Us" you'd know the less green the better.

Classic Girdle	Dug Out Girdle

How does this impact face up appearance in real world conditions? The answer from both GIA and AGS is that this is a negative feature and rightly so.  This photograph below is taken under GIA's newly released Diamond Dock which accurately depicts common daylight conditions.  It's rather obvious that the darker diamond on the right is the stone that would be disqualified from making a top grade and is indeed the stone used in the demonstration.  With the observation testing we've done in store with every day consumers, each person was able to make out and see these distinctions noting the difference in brightness.