Gemmology Today - Grade School 1
MICHAEL D. COWING is the author of
Objective Diamond Clarity Grading, an educator,
gemologist and appraiser operating an Accredited
Gemologist Association Certied Gem Laboratory.
His career in diamonds, gems, and gemology
spans 35 years.
The Ideal Brilliant Cut: Its Beginnings to Today
Introduction
Since its beginnings in the early 20th century to the present
day, confusion and misunderstanding has frequently
surrounded the use (or misuse) of the term “Ideal Round
Brilliant Cut,” its dening properties and origin. Some have
advocated eliminating its use altogether. Through the
examination of the Ideal Round Brilliant Cut’s (Ideal Cut
hereafter) evolution, this article endeavors to clear up its
history, clarify its dening properties and in the process
dispel the misunderstanding and mythology surrounding this
most popular of diamond cuts.
The computer generated images in Figures 1-3 provide a
preview of the Ideal Cut’s beginning in the 1860’s fashioned
with “35 degrees for the top angle and 41 degrees for the
back angle
1
.“ It was also known in Europe around the turn
of the 19th century as the American Cut. The Ideal Cut’s
appearance is transformed in Figures 4-6 with today’s
proportions, (larger table size, longer lower girdle facets,
thicker girdle, etc.), while retaining the same fundamental
crown and pavilion main angles which are key to its beauty.
The Ideal’s beginning with the American Cut
The beginning of today’s Ideal Round Brilliant Cut was the
design attributed to Henry Morse and his diamond cutting
rm who started cutting this form in the late 1860s. Morse
was credited with this “nely made”, brilliant cut in Frank
Wade’s 1916 book, “Diamonds” and by others including
Dr. Herbert Whitlock in “The Jewelers’ Circular Weekly”,
1917
2
. Morse’s design was rst called the “ideal brilliant” in
Figure 1. Face-up view of the Ideal
Cut at its beginning in the 1860’s
time frame.
Figure 2. 20° Tilt from face-up
view of the early Ideal Cut.
Figure 3. 20° Tilt forward from the side
view of the early Ideal Cut.
Figure 4. Face-up view of today’s
Ideal Cut with fundamentally the
same main angles as the early Ideal.
Figure 5. 20° tilt from face-up
view of today’s Ideal Cut.
Figure 6. 20° tilt forward from the side view
of today’s Ideal Cut.
Gemmology Today - Grade School2 September 2018
print in Whitlock’s writing on “The Evolution of the Brilliant
Cut Diamond”. There he concluded: “The nal stage in
the evolution of an ideal brilliant cut takes the form of the
American Cut brilliant.”
2
By the early 1900s other terms for
this same diamond arrangement included “Scientic Cut”,
and “Perfect Cut”
3
.
Quoting Wade: “A calculation made by the writer gives us
about the best angles for a diamond, [those attributed to
Morse], 35 degrees for the top angle and 41 degrees for
the back angle. Within two years of Wade’s book, Herbert
Whitlock echoed Wade: “Calculations ... have led to the
assumption of the ideal proportions of the brilliant cutting for
diamond to be close to the following: Top angle, 35°; back
angle, 41°”
2
.
In the early 1900s, cutting houses in London and Europe,
who were polishing diamonds for the relatively large and
burgeoning American market, were cutting to the lower
crown and pavilion angles of what they knew as the
American Cut that originated with Morse. Leviticus and
Polak , the Belgian authors of a 1908 Dutch encyclopedia on
diamonds gave credit to Morse and his shop foreman Field
for their work in diamond cutting advancements, in particular
the invention of an adjustable gauge for measuring cutting
angles. Wallis Cattelle in his 1903 book “Precious Stones:
A Book of Reference for Jewellers” explained, “The public,
seeing its superiority, began to insist upon having stones cut
and proportioned after his [Morse’s] method, and European
cutters were gradually obliged to conform more and more to
it. The result is that the proportions of the American brilliant
have been generally adopted.“
5
The Triple Cut Brilliant, 58 Facet Predecessor of the
Ideal Cut
With the advantage of hindsight, rather than Morse’s
American Cut being the nal evolutionary stage of the Ideal
brilliant as Whitlock stated in 1917, we see that this was
actually the Ideal’s beginning. From David Jeffries in his
publication: “Treatise on Diamonds and Pearls”
6
in 1750 we
know that the 58 facet brilliant existed going back at least
to the mid 18th century. It was later referred to as the “triple
cut” brilliant. This 58 facet design was most often fashioned
Figure 7. Jeffries’ 1750 drawings of the brilliant square and round versions. Whitlock refers to this style of
cutting as triple-cut. The 58 facet round triple-cut was the precursor of the Ideal Brilliant Cut.
as a square/cushion shape. However, we see from Jeffries
drawings, Figure 7, that it was also fashioned at that time as
a round brilliant.
For over a century, beginning with Jeffries (1750) and re-
afrmed by John Mawe (1813) until Morse, the best main
angles were said to be 45° for both crown and pavilion,
Figure 8.
Figure 8. John Mawe’s 1813 drawing showing the compass
used to make sure both crown angles and pavilion angles
were at 45°
7
Over that time however, the brilliant was typically cut with
greater depth and steeper angles than the prescribed 45°
crown and pavilion mains. The steeper, octahedral angles
of the diamond crystal “rough”, Figure 9, were more often
followed for maximum weight retention
8
, as diagramed by
Whitlock in Figures 10, 11 and 12.
Figure 9. Image of octahedral diamond “rough”
with angles steeper than 45° . Photo by Robison
McMurtry.
Gemmology Today - Grade School 3
Figure 10. 58 facet face-up diagram of triple-cut brilliant, the Ideal’s
forerunner. Diagrams by Whitlock
Figure 11. Tilted view of the mid-18th Century triple-cut
with octahedral angles.
Figure 12. Ray tracing by Whitlock in side view of 58 facet triple-
cut brilliant following diamond’s 54.7° octahedral angles
8
Figure 13. Top View of American Cut attributed to Morse.
Diagrams by Whitlock
Figure 14. Tilted View of American Cut.
Figure 15. Ray tracing by Whitlock in side view of
58 facet American Cut brilliant.
Gemmology Today - Grade School4 September 2018
The American Cut attributed to Morse was the same round
58 facet triple cut design, but with 41° pavilion main angles
and close to 35° crown main angles, Figures 13, 14 and 15.
The magic of Morse’s design was the change to these
angles from the 45° angles said to be the best by Jeffries
(1750) and Mawe (1813).
Tolkowsky’s Theoretical Validation of the Ideal Crown
and Pavilion Main Angles
The Ideal Cut’s design and angles that began with Morse
(late 1860s) received a boost in popularity in 1919 with
the publication by a young University of London graduate
engineer, Marcel Tolkowsky, and his publication, “Diamond
Design”. He was a member of a prominent diamond cutting
family, and related to another (Kaplan). Tolkowsky presented
mathematical calculations for what he called the high class
brilliant (40.75° pavilion angle, 34.5° crown angle and a
53% table). As Tolkowsky suggests, he, his father, and their
cutting rm were aware of and were at that time cutting to
the main angles of the American Cut, as he declared: “that
in the present day well-cut brilliant, perfection is practically
reached: the high-class brilliant is [currently] cut as near
the theoretic values as is possible in practice, and gives a
magnicent brilliancy to the diamond.”
9
Referring to the gradual shrinking-in of the corners of an
old-cut (square/cushion shape) brilliant, Tolkowsky notes
“Some American writers [likely referring to Wade, Cattelle
and Whitlock] claim that this change from the thick cut to
that of maximum brilliancy was made by an American cutter,
Henry D. Morse. It was, however, as explained, necessitated
by the absolute roundness of the new cut.
9
” Interestingly,
Morse’s shop foreman Charles Field is responsible for this
absolute roundness. He was rst to patent a mechanized
bruting machine that made the diamond perfectly round (in
use by 1870).
3
Aware that Tolkowsky’s calculations validated Morse’s
American Cut angles and design, Wade immediately
switched to emphasizing the importance of Tolkowsky’s work:
“Knowledge of the exact proportions required for the greatest
brilliancy should also be helpful to diamond dealers and
should make them more exacting in their requirements”
11
.
Wade later wrote that Tolkowsky’s father had already been
cutting to these proportions, and that “Tolkowsky Junior
found out why that shape did its work so well”
11
.
Tolkowsky’s Implied Range of Angles Possessing “The
Liveliest Fire and the Greatest Brilliancy”
In large part due to Wade’s inuence on trade understanding
of diamond cut quality and later on GIA’s support and
diamond course teaching, Tolkowsky’s work has had far
reaching inuence in the trade.
3
His exact theoretical
angles, 40.75° pavilion mains, and 34.5° crown mains
remain well known today. Because of today’s understanding
that there is a small range of angle combinations, not a
single combination like Tolkowsky’s that possess ideal
light performance, it is essential to know that the range of
angles of the ve diamonds, which Tolkowsky offered as
empirical proof of his calculations, varied substantially from
his theoretical ones. They provide a range of angles and
proportions that Tolkowsky saw as best. He describes the
ve diamonds as “all cut regardless of loss of weight, the
only aim being to obtain the liveliest re and the greatest
brilliancy
9
”.
Figure 16 is a computer image analysis of the light
performance of Tolkowsky’s ve examples of diamonds all
cut “to obtain the liveliest re and the greatest brilliancy
9
”
Each of these diamonds was identically illuminated in a
computer generated representation of jewelry store lighting
(utilizing DiamCalc
16
). It consisted of diffuse overhead
illumination coupled with numerous spot lights. In order
D1 40.75°, 35°& 56% D2 40.75°, 35°& 46.7% D3 40°, 34.5°& 61.9% D4 41°, 33°& 51.6% D5 41°, 34°& 47.7%
Figure 16. Tolkowsky’s ve example diamonds cut to give ‘the liveliest re and the greatest brilliancy
9
’
Gemmology Today - Grade School 5
D1 D2 D3 D4 D5
Pavilion Angle 40.75 40.75 40.00 41.00 41.00
Crown Angle 35.00 35.00 34.50 33.00 34.00
Table % 55.9 46.7 61.9 51.6 47.7
Lower Half % 60.0 60.0 60.0 60.0 60.0
Star Length % 40.0 40.0 40.0 40.0 40.0
Culet % 6.0 6.0 6.0 6.0 6.0
to reveal and emphasize any loss of brilliance from “light
leakage” or “observer obstruction” due to “retroreection,”
a black background and black area in the vicinity of the
observer’s head was employed.
Today’s Range of Angles with Ideal Light Performance
(Best Brilliance, Fire and Sparkle)
It is essential to pause here to put Tolkowsky’s top
performance diamond examples in today’s context.The
more exacting range of angles and proportions today found
to constitute Ideal in round brilliant diamond cutting was
investigated by the author and reported in the research
study, “Accordance in Round Brilliant Diamond Cutting”
13
and in the subsequent article, “The Central Ideal”
14
. These
explored the range of top grades for the cut grading systems
of the Gemological Institute of America (GIA), and the
American Gem Society (AGS). Both dene their top grades
(GIA Excellent and AGS 0 Ideal) to be in a narrow range of
angle combinations and proportions. They differ from each
other in some respects, but surprisingly and signicantly are
found to have a common geometric center.
The Graph for a table size of 56% in Figure 17
14
shows
the range of pavilion and crown angle combinations that
today constitute the Ideal 0 of AGS (blue + green), and
the Excellent grade of GIA (yellow + green). The angle
combinations in common (green) is the narrow range
considered both Ideal and Excellent. Their common
geometric center is the combination of Morse’s 41° pavilion
Figure 17. Graph of the ranges of the angle combinations graded Ideal 0 by AGS (Blue + Green), and Excellent by GIA (Yellow + Green).
The angle combinations in common (Green) is the narrow range considered both Ideal and Excellent. Also shown are the positions of the
Morse American Cut, the Tolkowsky theoretical angles, and the central Ideal angle combination, that is the geometric center both ranges
have in common. (The -4:1 slope ‘Ideal line’ in black indicates that a small change in pavilion angle is best coupled with about a four times
change in the opposite direction in crown angle to best maintain top light performance (best brilliance, re and sparkle). )
Gemmology Today - Grade School6 September 2018
angle (within 0.2°), a 34° crown angle and a 56% table,
Figure 17
14
. For reference purposes this combination
is termed the central Ideal
14
. Unlike Tolkowsky’s single
theoretical peak in light performance at 40.75° pavilion,
34.5° crown and 53% table, the central Ideal is simply the
center of the narrow ranges of angle combinations and
proportions that today are graded Ideal or Excellent
14
.
Also shown in Figure 17 are the positions of the Morse-
derived American Cut, the Tolkowsky theoretical angles, and
the central Ideal angle combination that is the geometric
center of both AGS and GIA ranges. Note also the “ideal
line” (drawn in black) called the “cutter’s line” by AGS. Many
cutters have long been aware that deviations from Morse’s
41° pavilion angle are best compensated by about a four
times change in crown angle in the opposite direction.
Cutting to angle combinations on or parallel to the ideal line
best retains top light performance (best brilliance, re and
sparkle) within the ideal range.
Comparative Analysis of Tolkowsky’s Five Diamond
Examples
Returning to the digital image analysis of Tolkowsky’s ve
diamond examples (cut “to obtain the liveliest re and the
greatest brilliancy
9
”), and armed with information from this
graph of the range in common with AGS’s Ideal and GIA’s
Excellent, we note Tolkowsky’s third example (Figure
16-D3) is the only one falling outside the top ranges of
both GIA and AGS. It has a too shallow 40° pavilion main
angle. This results in dark reections from the main facets
due to retroreection from the relatively dark vicinity of the
observer’s head. This darkness in the mains is apparent in
the faceup view in Figure 16-D3.
The author notes that closer observation of similar
diamonds possessing slightly shallow pavilion angles and/
or signicantly lower than 34° crown angles results in the
entire crown having less brightness compared with the Ideal.
This is due to retroreection from the halves in addition to
the mains, caused by the greater head obstruction brought
about by close viewing (roughly ten inches). At that distance
the observer’s head is obstructing a greater amount of light
from entering the diamond. This increase in head obstruction
when close viewing has a greater negative impact on the
appearance of slightly shallow cut diamonds than it does on
the Ideal Cut.
Research Study Findings from “Accordance in Round
Brilliant Diamond Cutting”
This 40° pavilion angle example supports the “Accordance
in Round Brilliant Diamond Cutting” study ndings, the rst
of which is the importance of cutting the Ideal’s pavilion
mains within a narrow range near the original 41° of
Morse. The center of the range of AGS 0 Ideal and GIA
Excellent angle combinations for the round brilliant cut is
Morse’s 41° for pavilion angle and closer to Tolkowsky’s
crown angle of 34.5° at 34°.
14
The central Ideal angle
combination of 41° and 34° is very close to both the angles
of Morse and Tolkowsky. In proper combination with the
other ve parameters dening the round brilliant cut, this
Ideal combination of 41° and 34° along with the angle
combinations of Morse and Tolkowsky are all in the narrow
range having the best light performance and beauty
13
.
The central Ideal combination of 41° and 34° is in accord
with the author’s ndings, and with the teaching of diamond
cutters and diamond cutting institutions. From the 1970s
the Institute for Technical Training in Antwerp, Belgium,
taught Ideal angle combinations of 41° and 34° - 34.2°
(pers. comm., D. Verbiest). In the same time frame, but a
continent away in Johannesburg, South Africa, the Katz
Diamond Cutting Factory taught its apprentices to cut the
Ideal round brilliant to a 41° pavilion main angle and 33°
to 35° crown main angle (pers. comm., P. Van Emmenis).
Basil Watermeyer, the renowned South African diamantaire,
and the author of “Diamond Cutting “, the “only one of its
kind” guide to diamond processing, gives the angles for “the
fully-proportioned Modern Ideal Cut [as] 32 - 34° crown, 41°
base.”
15
Comparative Analysis of Morse’s American Cut brilliant,
Today’s Ideal Brilliant Cut, and the Two Precursor Triple
cut Brilliants
We conclude with a comparative image analysis of the
light performance (beauty and appearance) of four diamond
cuts: two Ideal Cut forerunners, an 1860’s Ideal Cut, and a
modern Ideal Cut (Figures 18-25). It will become apparent
that much can be learned from this analysis, which utilizes
computer software systems (Octonus’ DiamCalc
16
) to
provide computer aided design (CAD) renderings of diamond
imagery. These images show a diamond’s light performance
in diagnostic, simulated illumination and viewing
circumstances. As before, each of these four diamonds is
identically illuminated in a representation of jewelry store
lighting with diffuse overhead illumination coupled with
numerous spot lights. A black background and black area in
the vicinity of the observer’s head is used to emphasize any
loss of brilliance from “light leakage” or “retroreection” from
the observer’s head.
The three viewing angles, in Figures 18-29, of these
four round brilliant cuts are 1. the faceup view looking
perpendicular to the diamond’s table, 2. faceup view tilted
away by 20°, and 3. side view tilted forward 20°.
Of these 12 images (see next page), one diamond’s view
stands out due to a total lack of light return in the table area
in the faceup view, Figure 19. This is the triple cut brilliant
with 45° crown and pavilion angles. This is particularly
surprising, since these angles were promoted by Jeffries and
Mawe, and espoused as perfect for over a century before
Gemmology Today - Grade School 7
Figure 18. 54.7°, 54.7°, 45%
Triple-Cut, Face-Up
Figure 19. 45°, 45°, 56 %
Triple-Cut, Face-Up
Figure 20. 41°, 35°, 45%
American Cut, Face-Up
Figure 21. 41°, 34°, 56%
Center of Today’s Ideal,
Face-Up
Figure 22. 54.7°, 54.7°, 45%
Triple-Cut, Tilted Away 20°
Figure 23. 45°, 45°, 56 %
Triple-Cut, Tilted Away 20°
Figure 24. 41°, 35°, 45%
American Cut, Tilted Away 20°
Figure 25. 41°, 34°, 56%
Center of Today’s Ideal,
Tilted Away 20°
Figure 26. 54.7°, 54.7°, 45%
Triple-Cut, Side View Tilted
Forward 20°
Figure 27. 45°, 45°, 56 %
Triple-Cut, Side View Tilted
Forward 20°
Figure 28. 41°, 35°, 45%
American Cut, Side View Tilted
Forward 20°
Figure 29. 41°, 34°, 56%
Center of Today’s Ideal, Side
View Tilted Forward 20°
Whitlocks
Drawing
54.7 Degree
Triple-Cut
Jeffries’/
Mawe’s
45 Degree
Triple-Cut
Morse
Ideal
Today’s
Central
Ideal
Pavilion Angle 54,7 45 41 41
Crown Angle 54,7 45 35 34
Table % 45 56 45 56
Lower Half % 40 30 60 77
Star Length % 60 50 40 55
Culet % 10 10 5 0
Girdle Tickness % 0 0 0 3
Figure 30. Angles and Proportions of two Ideal forerunners, the Ideal’s Beginning, and Today’s Ideal.
Gemmology Today - Grade School8 September 2018
range of angle combinations today considered Ideal. Morse’s
crown and pavilion main angles, key to the Ideal’s beauty,
have stood the test of time. The range is narrow, and as
we saw with Tolkowsky’s example diamond, Figure 16-D3,
any signicant deviation from this angle combination, or the
central Ideal combination 41° pavilion, and 34° crown results
in diminished light performance.
The narrow range of angles around the central Ideal that
today are graded both Ideal and Excellent includes both
Tolkowsky’s theoretical angles, and the Morse American Cut
angles that in the early 20th century were rst called Ideal.
Acknowledgments
The outstanding research by Al Gilbertson over a six year
period is beautifully organized and presented in his book,
American Cut - The First 100 Years. Without the aid of this
conscientious and comprehensive endeavor, and access to
the book’s extensive source Bibliography and detailed Index,
this study article would lack the historical authority and
validity made possible by a study of his book. Everyone is
encouraged to further pursue this legacy of the Ideal Brilliant
Cut and its beginning as the American Cut by availing
themselves of a free online copy of his book.
https://archive.org/stream/AmericanCut--theFirst100Yea
rsTheEvolutionOfTheAmericanCutDiamond/Gilbertson-
americanCut-2007_djvu.txt
OctoNus’s DiamCalc
16
software system is the resource and
tool essential to production of the photorealistic renderings
of diamond light performance that illustrate this study and its
ndings. It is a one of a kind capability that the author nds
is critically important to research in diamond cut design and
light performance.
See http://www.octonus.com/oct/products/3dcalc/standard
Thanks to Geoff Dominy, founder of the World Gem
Foundation and author of the Handbook of Gemmology,
a tour de force in gems and gemmology. Geoff has kindly
taken on the editing, and publishing aspects of this article.
Footnotes
1. Wade , F. (1916), “Diamonds - A Study of the Factors that
Govern their Value”, G.P. Putnam’s Sons, New York and The
Knickerbocker Press, London.
2. Whitlock, H. (1917a), “The Evolution of the Brilliant Cut
Diamond”, The Jewelers’ Circular-Weekly, Vol. 74, No. 1, pp.
115-121
3. Gilbertson, A. (2007), “American Cut - The First 100
the time of Morse.
With today’s knowledge, and the clear evidence in Figure
19, we now recognize that a diamond cut with 45° pavilion
angles, when viewed faceup, retroreects rays in the table
from the vicinity of the viewer’s eyes and head resulting in
the dark table appearance known today as a “nailhead”.
The dark table nailhead appearance is the reason the 45°
pavilion angle is one of the poorest angles to cut the round
brilliant pavilion (see article “Let There Be Light”
12
for further
discussion of retroreection and the poor cutting called the
nailhead.)
Notice in Figure 23 that the 45° triple cut of Jeffries
brightens in the table when sufciently tilted from the faceup
view, in this instance by 20°, but it still has less re than the
much steeper triple cut in Figure 18 and 22. It exhibits far
less brilliance whether faceup or tilted than does the early
Ideal in Figures 20 and 24 or the equally brilliant modern
Ideal in Figures 21, 25 and 31. (More can be learned from
this comparative analysis that must be left for another time.)
Conclusion
Whether cut with the smaller table, larger pavilion main and
shorter half facets of the early Ideal (Morse’s American Cut),
or fashioned with the larger table, slimmer mains and longer
halves of today’s Ideal, the images, Figures 20, 21, 24, 25
and 31 reveal the superior light performance of re and
brilliance that characterize the Ideal Brilliant Cut.
The other angles and proportions of the Ideal Cut, most
importantly table percent and lower half facet angle (or
length) have changed. However, Morse’s combination 41°
pavilion angle, and 35° crown angle remains in the narrow
Figure 31. Modern Ideal Cut Diamond
(Photo by Michael D. Cowing)
Gemmology Today - Grade School 9
Years”, The Gemological Institute of America, Carlsbad,
California, p. 41.
4. Leviticus, F. and Polak, H. (1908), De Bewerking van hat
Diamant, De Erven F. Bohn, Haarlem, Belgium, pp. 46-49,
254-255.
5. Catelle, W. (1903), “Precious Stones: A Book of
Reference for Jewellers”, J. B. Lippincott Co., Philadelphia,
pp. 57, 59-62, 65.
6. Jeffries, D. (1750), “A Treatise on Diamonds and Pearls”,
2nd Edition, C. and J. Ackers, London, PP. 13, 21-25.
7. Mawe, J. (1823), “A Treatise on Diamonds and Precious
Stones”, Longman, Hurst, Rees, Orme, and Brown,
Paternoster Row, London, pp. 47-48, 60.
8. Whitlock, H. (1917a), “The Evolution of the Brilliant Cut
Diamond”, The Jewelers’ Circular-Weekly, Vol. 74, No. 1, pp.
115-121
9. Tolkowsky, M. (1919), “Diamond Design”, E. F. N. Spon,
Ltd., London, PP. 6, 23-25, 94-95, 97-104.
10. Wade, F. (1915), “Cutting or Make and its Effect on the
Value of Diamonds”, The Jewelers’ Circular and Horological
Review, Vol. 71, No. 5, pp. 53-54.
11. Wade , F. (1928), “Some Interesting Notes on Zircon”,
The Jewelers’ Circular, Vol. 97, No. 7, pp. 54-55.
12. Cowing, M, (2018), “Let There Be Light”, Gems &
Jewellery /Spring/ Volume 27 / No. 1
13. Cowing, M. (2007), “Accordance in Round Brilliant
Diamond Cutting”, The Journal of Gemmology, Volume 30
No. 5/6.
14. Cowing, M. (2009), “The Central Ideal”, Gems &
Jewellery /April / Volume 18 / No. 2
15. Watermeyer, B. (1982), “Diamond Cutting, A complete
Guide to Diamond Processing”, Centaur Publishers,
Johannesburg, p. 166.
16. DiamCalc, Octonus Software, http://www.octonus.com/
oct/products/3dcalc/standard
References
Cowing, M. (2007), “Accordance in Round Brilliant Diamond
Cutting”, The Journal of Gemmology, Volume 30 No. 5/6.
Cowing, M. (2009), “The Central Ideal”, Gems & Jewellery /
April / Volume 18 / No. 2
Cowing, M, (2018), “Let There Be Light”, Gems & Jewellery /
Spring/ Volume 27 / No. 1
Catelle, W. (1903), “Precious Stones: A Book of Reference
for Jewellers”, J. B. Lippincott Co., Philadelphia, pp. 57, 59-
62, 65.
DiamCalc, Octonus Software, Http://www.octonus.com/oct/
products/3dcalc/standard
Gilbertson, A. (2007), “American Cut - The First 100 Years”,
The Gemological Institute of America, Carlsbad, California.
Leviticus, F. and Polak, H. (1908), “De Bewerking van hat
Diamant”, De Erven F. Bohn, Haarlem, Belgium, pp. 46-49,
254-255.
Jeffries, D. (1750), “A Treatise on Diamonds and Pearls”, 2nd
Edition, C. and J. Ackers, London, PP. 13, 21-25.
Mawe, J. (1823), “A Treatise on Diamonds and Precious
Stones”, Longman, Hurst, Rees, Orme, and Brown,
Paternoster Row, London, pp. 47-48, 60.
Tolkowsky, M. (1919), “Diamond Design”, E. F. N. Spon, Ltd.,
London, PP. 6, 23-25, 94-95, 97-104.
Wade, F. (1915), “Cutting or Make and its Effect on the
Value of Diamonds”, The Jewelers’ Circular and Horological
Review, Vol. 71, No. 5, pp. 53-54.
Wade , F. (1916), “Diamonds - A Study of the Factors that
Govern their Value”, G.P. Putnam’s Sons, New York and The
Knickerbocker Press, London.
Wade , F. (1928), “Some Intreresting Notes on Zircon”, The
Jewelers’ Circular, Vol. 97, No. 7, pp. 54-55.
Watermeyer, B. (1982), “Diamond Cutting, A Complete Guide
to Diamond Processing”, Centaur Publishers, Johannesburg,
p. 166.
Whitlock, H. (1917a), “The Evolution of the Brilliant Cut
Diamond”, The Jewelers’ Circular-Weekly, Vol. 74, No. 1, pp.
115-121
