Sunday, April 20, 2008

Peer review of Cutting standards by AGS

Here is part of the continuing conversation about cutting going on the Polygon site. This is the response to a gentleman stating that Tolkowski had the advantage of peer review when he wrote his thesis on diamond cutting in the early 1900's.

Turns out that the AGS had extensive peer review, even if they did not make a lot of noise about it!


Bill, I hate to correct you on this, but you are wrong. As
you know I chaired the Gemological Sciences Committee during
the time we were coming up with the cut grade system for the
AGS Laboratory. Let me tell you about peer involvement and

First, the chairman of the committee has a Ph.D. in
inorganic chemistry with an extensive background in research
at the university level (just happens to be me).

Second, the committee consisted of jewelers with scientific
backgrounds, cutters, retailers, suppliers, lab people, etc.

Third, in keeping with scientific protocol we approached the
problem from two standpoints-theoretical and experimental.

Fourth, our experimental work was guided by a Ph.D. in
optics who heads up optical research at one of our nations
finest universities.

Fifth, our theoretical work was carried out by a team of
scientists from a foreign university well known for work in
this field.

Sixth, also in keeping with scientific protocol for
acceptance of scientific developments and material for
publication we employed a peer reviewer to look over the
shoulders of what the other two groups were doing(augmented
by work done by employees of the AGS Laboratory). We were
adamant that no system would be implemented until such time
as the peer reviewer put in writing that our science was
impeccable and that we were clear, from a scientific
standpoint, to go public. That peer reviewer was a
distinguished professor in optics at a different university
and editor of a major journal in that field.

Seventh, so much for the science. What all that yielded was
mountains of paperwork with both theoretical calculations
and actual measurements on the behavior of light in crystal
systems. The results were made graphic in contour diagrams
that showed the different dimensions and angles that
represented the maximum return of light, taking into
consideration a multitude of environmental factors. Now,
here's the kicker, during the years we studied those
experimental/theoretical diagrams, one person on the
committee kept reminding us over and over again with
statements like, "yes, that particular configuration does
seem to handle light better than others, BUT will that stone
appear to be beautiful to the eye."

I should also point out that it took the committee several
years to arrive at the AGS cut grading standards.

One amazing discovery came out of all that work. After all
the science is applied to the system, when one looks at the
areas on the contour diagram where light seems to be handled
best, right in the center of that area sits Mr. Tolkowsky's
ideal cut.
What all this leads to is the circumstance that when a
jeweler is getting ready to show a customer a diamond that
has the AGS triple zero designation, and even before the
paper is opened, he can be assured that the diamond has been
cut to the most exacting of geometric proportions and that
it will be beautiful to look at.

Perhaps others on this board with knowledge of how the other
laboratories arrived at their cut grading standards would be
willing to share that with the rest of us.

Chris Bramlett

Saturday, April 19, 2008

A discussion about H & A cutting

This is one of the best dissertations I have ever seen on the term Hearts and Arrows. It was made by a friend of mine, John Pollard and it was his second ever post on Polygon. Even the professionals who post there were impressed with what he had to say, and I offer it to you for your reading pleasure.

You can see our selection of fine Hearts and Arrows quality cut diamonds at Hearts and arrows cut diamonds.

Enjoy the read, it is a good one.


Quoted from

I don't like the term "H&A" because it's been turned into a
gimmick. I prefer the term cut precision, since that's what
is necessary to acquire the "H&A" pattern in rounds (other
patterns appear in different shapes); the facets aligning so
precisely with their opposites that the reflections overlap
when seen in reflective viewers.

From a production standpoint it's best to get your
priorities straight:

1. Just because a diamond shows the "H&A" pattern (no matter
how precise) does not mean it has premium light performance.
Light performance is far more important for appeal. If I
had only two diamonds, an AGS Ideal (performance) without
strict H&A...and a diamond cut to H&A precision with
geometry that did not produce top light performance...I
would certainly elect the one with top light performance as
a "better" diamond in terms of appeal (not cut precision).
Fortunately these days you will usually (not always) find
that "H&A" diamonds have pretty good c/p angles. This
is simply evolution.

2. In diamonds with top light performance the benefits of
precise cut precision ("H&A) in rounds are contrast and
consistency in performance. Cut precision increases
contrast between light & dark areas, appealing to the
natural edge detection hard-wired into human physiology,
strengthening intensity and evaluated in our top systems as
"contrast brilliance" (AGS) or "pattern" (GIA). For those
who have not read the landmark paper in last September's
"Optical Engineering" it's fantastic. Coupled with
appropriate table, c/p angles and lower halves the net
effect is intensity in scintillation as well as broader
spectral flares (an issue of taste of course). These
effects are maximized in near-Tolkowsky configurations but
if the lower halves are too short, or the table too large
the diamond can take on too much obscuration (AGS) or
obstruction (GIA) - penalized in those systems. On the
other hand, some people prefer the random look of asymmetry
over precise H&A diamonds, just as others prefer other
shapes. Diamond beauty is always subject to taste.

3. Diamonds with a level of optical symmetry 'close to' what
purists consider H&A can mimic the optical effects... As
our evaluative devices and cutting equipment have improved
over the last decade there are diamonds produced with
better-than-average optical symmetry that are simply a
by-product of blocking to top proportions sets; what some
cutters call a "happy accident." This is where controversy
reigns: Diamonds displaying the highest levels of optical
symmetry; those crafted to the top levels of cut precision
and the original Japanese standards for supersymmetry
on-purpose, are valued by enthusiasts and collectors for
their ultimate craftsmanship, as much as any effects on
performance... This is no different than people who value
IF for rarity, not a tangible visible difference over lower

It's unfortunate that there is no authoritative definition
of how tight cut precision must be in order for a diamond to
be officially called "H&A." Every dealer or manufacturer is
defining them by his/her own standards. Dealers who
don't have access to rarified top cut precision will define
the "happy accident" stones they can get as "H&A" (looky
looky). The purists band their steins on the bar and cry
foul. This causes confusion for consumers. With no
concrete definition the situation is akin to sellers in the
early 1900s inventing their own "A" and "AAA" grades for
color to one-up the guy next door. Until the GIA set forth
standards for color and clarity it was it is
for "H&A" dealers today. Logically, the purists take great
pride in the fine-make craftsmanship they respect and value
- as they should, it's remarkable work! But the purists are
far rarer than those willing to "make a buck" by turning H&A
into a gimmick. People selling "whatever" under that label
are diluting what could be a really cool niche product.

In a perfect world I think H&A marketing would focus on top
light performance as the priority, amplifying the optical
benefits (which can be a taste factor) and rarity in cut
quality (the most precisely cut H&A diamonds are rarer in
terms of cut precision than D is in terms of color). To me
the finest H&A diamonds are a subsection of round brilliant
- for which we have several successful makes whether you're
talking 60/60, near-Tolk, high-crowned or antique cuts
which were predecessors to the modern RB. People are going
to like different looks and some will have a taste for one
round over another, just as others may like squares or
fancies. Different strokes for different folks. There's
enough business out there for all of us - if you can find
out what makes your customer tick.

John Pollard