Thu, 01 Sep 2005

Numbers and perception, the case of square diamond-cuts

a previous article, I briefly touched the aspect of perception in our
judgement of numbers. I made the case, that since most diamond
professionals first gather their knowledge with round brilliants, that
they automatically apply rules for rounds to fancy shapes. This is also
true with numbers.

In this article, I will give you some examples how numbers and perception can interact.

Example 1. An AGS-0 princess-cut, Crafted by Infinity

Here are the basic measurements for this stone, as mentioned on the AGS-report:

Weight: 1.257 Cts.
Measurements: 5.78 x 5.78 x 4.60 mm.
Total depth: 79.6%
Table %: 59.7%
Crown angle: 32.8°
Crown height: 11.2%
Pavilion angle: 42.7°
Pavilion depth: 64.9%
Girdle 2.7% to 3.8%
Culet: Pointed

Example 2. The same diamond, but with the measurement noted in the same way as for a round brilliant

In a round brilliant, all percentages are calculated as a percentage of the average diameter, while in fancy shapes, they are calculated as a percentage of the smallest
diameter. Let us now show you the measurement of the same diamond, but
this time according to the normal notation of a round brilliant.

Weight: 1.257 Cts.
Measurements: 8.17 x 5.78 x 4.60 mm.
Total depth: 65.9%
Table %: 49.4%
Crown angle: 32.8°
Crown height: 9.3%
Pavilion angle: 42.7°
Pavilion depth: 53.8%
Girdle 2.2% to 3.1%
Culet: Pointed

looking at the figures, these measurements look a lot better than in
the first example. First, it clearly shows the diameter from
point-to-point being 8.17 mm. Also, the total depth-notation went from
79.6% to 65.9%, which sounds a lot better, especially since we are used
to depths around 60% in round brilliants.


Examples 3 & 4
Example 3. The same diamond, but depth measured in relation to the longest diameter

us take the example a bit further even. Here are the measurements, if
we take the depth and table in relation to the longest diameter of

Weight: 1.257 Cts.
Measurements: 8.17 x 5.78 x 4.60 mm.
Total depth: 56.3%
Table %: 42.2%
Crown angle: 32.8°
Crown height: 7.9%<
Pavilion angle: 42.7°
Pavilion depth: 45.9%
Girdle 1.3% to 1.8%
Culet: Pointed

Wow. Did you see that total depth? Only 56.3%, that must be a whopping spready stone.

I admit, I am truly exaggerating with mathematical wizardry in this
example. After all, statistics can prove anything. I just wanted to
show that the way measurements are noted, can give a totally different
feeling about the diamond. In this sense, the difference between
example 1 and 2 are important, since we are just using the
notation-rules of rounds in example 2. Knowing that most of our
knowledge in diamonds started in round diamonds, and that we are
extremely used to measurements of rounds, example 2 is an example in
which we are truly comparing apples to apples.

Example 3 is exaggerated, I admit, but take a look at this example.

Example 4. Measurement of a Dream Diamond by Hearts-on-Fire

Dream Diamond is a trademarked proprietary square cut diamond, marketed
by Hearts-on-Fire. We have taken the following example from the
Hearts-on-Fire-website ( with stocknumber DRM6048.

Weight: 1.258 Cts.
Measurements: 7.12 x 5.94 x 4.41 mm.
Total depth: 61.9%
Table %: 55.0%
Pavilion angle: 40.9°
Girdle 1.2% to 1.4%
Culet: Pointed

diamond is a very symmetrical square stone, and the diameter from
side-to-side is 5.94mm. Because of the cut corners, the diameter from
point-to-point is 7.12mm. The total depth is noted in relation to the
highest diameter (4.41 divided by 7.12 is 61.9%). It is logical to
assume that the table and girdle percentages are also in relation to
that highest diameter.

With the Dream Diamond being a proprietary
cut, the company itself can choose how the measurements are presented.
It is interesting to see how Hearts-on-Fire has chosen to represent its
stone as in our example 3.

The result of this choice is obvious.
The total depth-percentage and the table-size look very similar to what
we are used to in round brilliants. At the same time, crown height is
not mentioned, because (as we can see in example 3), this would look
very low compared to what we are used to in rounds.


the previous examples, you can see that the way a diamond’s
measurements are reported is subject to certain choices or rules. Any
professional should be aware of these choices, since they have an
effect on how these measurements will look.

Since almost all of
us have been trained in round brilliants, we have a tendency to
immediately compare certain measurements to what we are used to in
rounds. This article shows that this could lead to incorrect