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The Holloway Cut Advisor (HCA)
We created this page because we are
often asked "What are your thoughts on the Holloway Cut Advisor?" and we
thought it would be nice to put our thoughts into words so that we can
stop answering that question on the telephone all day =)
There is some credence to the concept behind the
Holloway Cut Advisor (HCA) and it certainly is a good way to narrow
down the list of possibilities when considering a variety of diamonds…
However, we don’t consider the HCA to be 100% conclusive and we say this
knowing that most of the diamonds in our inventory 'score' extremely well
on the HCA. No doubt that Garry Holloway would agree, the HCA is a
"work in progress" and as such it is continually being fine tuned and
upgraded just as our selection process is continually fine tuned and
updated as cutting technology advances.
If you have been watching the development of the HCA for as long as we
have, then you know that a diamond which scored exceptionally well on the
HCA two years or so ago would not score as well today. The fact is
that the quality of diamond cutting will continue to improve as technology
advances and the diamonds we sell today are not likely to be as well cut
or as fine tuned as the diamonds we will be selling five years from now.
Likewise, a diamond which scores well on the HCA today, might not score so
well at some point in the future as the parameters for the HCA change
based upon Garry's current research.
The challenge with the HCA is that too many people seem to take the
results as an absolute measurement of a diamond's visual
performance while it is merely an indication of the potential
possibilities because the results are based upon mathematical ray
tracing and not all of the information is taken into account... Here
is part of the challenge as we see it… The HCA estimates the visual
performance of a diamond based on the measurements of the four primary
factors that determine the proportions rating of a round brilliant cut
diamond, the total depth, the table diameter, the crown angle and the
pavilion angle… The measurements for these four factors are based upon
the average of forty measurements that were determined by
Sarin DiaMension computerized
proportions analysis. The challenge with averages is that people rarely
look past the results to consider what the average measurements are based
upon. In other words, the diamond you are considering might have an
average crown angle of 34.5 degrees, however that average could be based
upon a tight range of 34.3 – 34.7 degrees or it could be the result of a
high and low range of 34.0 to 35.0 degrees and this type of a swing
between the high and low measurements would have a dramatic effect upon
the visual performance of a diamond… Thus while we believe that the HCA
is of considerable value to the diamond buying public, it is merely one of
the first stepping stones on the path to selecting a beautiful diamond.
If all you want is a diamond that scores well on the HCA (Excellent for all factors) then all you have to do is find a diamond with the following measurements:
Total Depth under 60.3 if you want
the diamond to score Excellent for all four factors…
Table Diameter anywhere between 53 – 57%
Crown Angle anywhere between 33.7 – 34.8 degrees.
Pavilion Angle anywhere between 40.4 – 40.8 degrees.
If you stop reading here, you will
be doing yourself a tremendous disservice. The range of proportions
stated above is simply too broad of a range for our liking and it leaves
considerable room for error. To be clear, we're not all that fond of
diamonds with a 33.7 degree crown angle and a 40.4 pavilion depth, but the
range is excellent if you know how to combine certain combinations of
crown and pavilion angles within the range... In other words, you
have to know how to combine the right crown angle with the right pavilion
angle, in this way we feel that the HCA leaves too much to chance.
Let's play with the HCA,
click
here to open the HCA in a new window
Using a Total Depth of 60.3% create a diamond which scores Excellent for all factors considered by the HCA, something like:
Table Diameter 55%
Crown Angle 34.5 degrees
Pavilion Angle 40.8 degrees
Now increase the Total Depth to 60.4% and the Spread of the stone (the relationship between the total depth of the stone and the outside diameter) just dropped to Very Good and the rating will only change 0.3% if you increase the Total Depth all the way up to 62.9% and the rating for Spread will drop to Good if you increase the Total Depth to 63%
Change the Total Depth measurement back to 60.3% and increase the Pavilion Angle to 40.9 degrees and now the scintillation will drop to Very Good while all of the other factors remain at Excellent.
Change the Total Depth of the diamond back to 62.9% and drop the Pavilion Angle back down to 40.8 degrees, the diamond will Score 1.4 Excellent with Excellent for the first three factors and Very Good for spread. But is a total depth of 62.9% really very good in terms of spread? We certainly don’t think so… It will significantly decrease the outside diameter of the diamond which means that the diamond you purchase will ‘face up’ smaller than a diamond of comparable weight and proportions that had a total depth under 61.8%.
Now, there is some truth to the theory that certain combinations of proportions produce diamonds that tend to have higher visual performance than standard ideal cut diamonds… However, we believe that the range is much tighter than the range that is acceptable to the HCA for the moment. And for the record, we happen to find the visual performance of a round brilliant cut diamond with a 40.9 pavilion angle to be exceptional in many cases assuming that the crown angle, table diameter and total depth are complimentary. We use a proprietary system to measure the reflective index of the diamonds that we evaluate for our inventory and some of our best scores come from diamonds that have a 40.9 degree pavilion angle so we urge you to keep your mind open to the possibility of a 40.9 pavilion angle despite how it affects the scintillation rating as determined by the HCA. The fact is that when the Japanese designed the Hearts & Arrows diamonds over a decade ago using state-of-the-art computer animation and ray tracing technology, the target for the pavilion angle was exactly 40.9 degrees. And the HCA used to score diamonds with a 40.9 degree pavilion angle very well until the last update...
An important thing to understand is
that the ‘range’ for the ‘zero ideal cut diamond’ is exactly that, it is a
range… And as such, it has a high and a low end (probably to appease some
of the diamond cutters who might not use the AGS Laboratory if the range
of proportions for the ideal cut diamond was tighter) but it is the middle
of the range that was more likely the intended target when the range was
developed and not the outer extremes. Our research supports this theory
and as a result many of the diamonds listed for sale within our
Private Reserve have proportions that fall
within the center of the range for the ideal cut diamond rating and
subsequently tend to score extremely well on the HCA.
Here is the range of proportions and factors that we find produces ideal
cut diamonds with exceptional visual performance more often than not… We
actually refer to a diamond cut to the following specifications to be
(Ideal)3™
‘Super Ideal’ as opposed to merely being ideal cut:
Total Depth between 59 – 61.8% (only
effects the diameter of the stone)
Table Diameter between 53 – 57% (least critical factor)
Crown Angle between 34.3 – 34.8 degrees
Pavilion Angle between 40.6 – 40.9 degrees
Girdle: prefer 0.7% thin up to 1.8% medium, faceted
Culet: GIA none or AGS pointed (same thing, different terms)
Polish: GIA Excellent / AGS Ideal (the highest from each lab)
Symmetry: GIA Excellent / AGS Ideal (the highest from each lab)
Now before you go running off
thinking that we’ve handed you the recipe for the secret sauce, there are two things we
would like you to understand… The first is the previous statement that
this combination of proportions and factors tends to produce ideal cut
diamonds with exceptional visual performance more often than not… This
combination of ‘Super Ideal’ proportions is a good beginning, but it only
works well if the cutter bothered to cut the diamond in correlation with
the orientation of the grain of the diamond and thus we sometimes see
ideal cut diamonds cut to these proportions that still fail to meet our
expectations for brilliance, dispersion and scintillation. The
‘orientation of the grain’ of a diamond is the direction that the grain of
the crystal runs through the stone… Our average rejection rate when
evaluating ideal cut diamonds for our inventory after sifting through the
paper is 40%.
The second concept we would like you to grasp is that there are other
combinations of proportions within the range of ideal that deliver similar
visual performance, they are just a little trickier to combine and require
a little thought which is what you have us for... Essentially the combination calls for a shallow crown
angle combined with a deeper pavilion angle, something like a crown angle
of 33.9 degrees combined with a pavilion angle of 41.0 to 41.2 degrees,
but it doesn't always work.
The opposite combination is likely to produce similar results, for instance a
steeper crown angle of something like 35.3 degrees combined with a shallow
pavilion angle somewhere in the range of 40.4 – 40.5 degrees.
However there are no hard and fast rules when it comes to selecting a
diamond by the numbers, there is merely an increased possibility of
success which is why we insist on personally evaluating every diamond that
we buy for our Private Reserve while most
of our 'competition' sells diamonds by merely republishing the multiple listing
directory of diamonds that are available to the trade. You know the
'competitors' that we’re referring to, they’re the ones advertising things
like “an
inventory of more than 50,000 diamonds”… They rarely see the diamonds
that they sell, they merely list diamonds for sale and then have the
diamonds drop shipped from their suppliers to their customers… We on
the other hand prefer
to buy diamonds to the old fashioned way... We look at them ☺
So you're probably wondering whether we use the HCA as part of our selection process?
Well no, not
really. We look at it so that we can answer your question "so how
does it score on the HCA" but that's about the extent of our use of the
program. We have our own ways of evaluating the diamonds that we buy
for inventory which includes the use of gemological equipement and a whole lot of diamond buying
experience!
If by chance you happen to be considering a diamond that is listed by five
or six different on-line diamond dealers and you would like us to try and
source it for you and evaluate it on your behalf using our standard
grading practices we will be happy to do so. Simply
email us
with the specifics of the diamond and we will run a search for it through
the multiple listing services and attempt to source it for you. We
will match the price of any legitimately advertised diamond.
While we do not buy diamonds based upon the results of the HCA, we do pay
attention to the development of the program and the changes being made to
the HCA by Garry Holloway because we believe that his "work in progress"
is an excellent tool for the diamond buying public to use as part of their
evaluation process... We merely want people to be aware that the HCA
is not 100% conclusive and that nothing beats an experienced set of eyes,
for this reason we recommend taking the time and paying the small expense
to have your diamond purchase evaluated by an
Independent GIA Gemologist Appraiser regardless of whether you buy it
on-line from us or another dealer or your local retailer.
May we help you find the diamond of your dreams?
Send us an email diamonds@niceice.com
and tell us what you are looking for.
Or give us a call at 206.319.8152 or Toll Free 877.844.5443
Copyright © 1996 - 2007 Nice Ice, Inc.
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