GEMLAB REPORT:
December 1997 - Issue #6
By: Ted Themelis
themelis@ganoksin.com
In This Edition:
- Pink Sapphire or Pale Ruby?
http://www.ganoksin.com/borisat/nenam/gemlab6.htm
One of the most controversial and still unresolved issues for
the gemological community is the appropriate definition of, or
relationship between, pink sapphire and ruby. Generally, in
the marketing of color designations of ruby and
pink sapphire tend to refer to rubies as gems that are medium
to dark red to orange or purplish-red and to pink sapphires as
pale to light red. Both gemstones are, of course, color
varieties of corundum.
The issues.
The question of definition arises because of three major
issues: 1) Whether or not pink sapphire should be considered
as an individual color variety of corundum. 2) If each color
variety is to be considered separately, at what point the
demarcation line between ruby and pink sapphire occurs? 3)
What are the proper lighting conditions to be used to
determine their exact color?
Gemstone dealers and jewelers have argued on these issues for
years. The goal of many dealers is to buy the gem as pink
sapphire and sell it as ruby, because in most cases rubies are
considered more valuable than pink sapphires and therefore
produce more profit.
Historical aspects.
Before any attempt would be made trying to resolve this
problem, it might be wise to look at the historical aspects of
the issue. Max Bauer, in his Precious Stones (1896), gives the
following definition of ruby:
“The tone of color (in ruby) differs in different specimens,
being sometimes deep and intense, sometimes pale and light.
The lighter shades vary from pale rose-red to reddish-white,
some specimens being so faintly tinged with red as to appear
almost colorless. The darker colors are pure red, carmine-red,
or blood-red; the red of the majority of rubies, however, has
a more or less distinct tinge of blue or violet, this being
specially noticeable in transmitted light. The shade of color
most admired is the deep, pure carmine-red, or carmine-red
with a slight bluish tinge.”
A few years later (1909), Julius Wodiska describes ruby in his
Book of Precious stones:
“The color-tone of the ruby varies greatly, and the presence
of deep, intense tones of red causes the term ‘masculine’ to
be applied to a gem while the paler tints suggest the term
‘feminine.’ Rubies range from a delicate pink tint through
pale rose-red to reddish-white, pure red, carmine red, or
blood red. A tinge of blue or violet is frequently discernable
in these shades.”
So, here we have introduced the designations “masculine ruby”
and “feminine ruby”! Although the term “pink sapphire” has not
been mentioned so far, there is an indirect attempt to
separate the deep red corundum’s (“masculine”) from “feminine”
rubies, the lighter red corundums. Some speculation has it
that the “feminine” ruby represents Sri Lankan material, while
“masculine” ruby represents Burmese or Thai material.
Obviously, such designations were devised to emphasize the
existing differences between “masculine” and “feminine” rubies
and to prevent potential misunderstandings.
Early reference to pink sapphire in gemological literature is
given by G.F. Herbert in the sixth edition of Gemstones
(1930):
“The tint of the red stones varies considerably in depth;
jewelers term them, when pale, pink sapphires, but of course,
no sharp distinction can be drawn between them and rubies.”
From that time until now, the designation “pink sapphires” has
appeared in every gemological publication. Reference to it is
made, for example, even by R.M. Shipley in The Dictionary of
Gems and Gemology:
" Ruby. The red variety of corundum. Intense, medium to medium
dark purplish red (so-called pigeon’s blood) is best, intense
red is fine, and dark red is less desirable. Star ruby is
rare. In the jewelry industry, the finest purplish-red stones,
principally from Burma, are known as ‘Burma,’ or ‘oriental
rubies’; less valuable, darker red, principally from Thailand,
as ‘Siam rubies’; and light red, from Ceylon and elsewhere, as
‘Ceylon ruby’ or pink sapphire."
R.Webster describes ruby in his monumental Gems (4th ed.,1983)
as follows:
“Ruby varies in shade from a pale rose tint through all shades
of red to a deep crimson sometimes known in the jewelry trade
as ‘black.’ The pink colored corundum may be considered as a
pale ruby but a pure pink colored stone is known as pink
sapphire, all fancy colored corundum’s being termed sapphire
with the color as prefix. The decision whether a stone is pink
sapphire or pale ruby may often lead to debate.”
Discussion.
The need to define ruby specifically as a color variety of the
gem species corundum is obvious, whether the material is
called “masculine ruby”, or “oriental ruby”, or “Sian ruby”,
or anything else. Yet one side in the debate over names argues
that since pink sapphire is light red - rather than a
different color completely - there should be no distinction
made between ruby and pink sapphire at all. In fact, the Asian
Institute of Gemological Sciences (AIGS) in Bangkok, Thailand,
has abandoned the use of the pink-sapphire designation (as an
individual variety of corundum) from its educational programs,
as well as from the gem-identification reports.
The opposing side argues that pink is an entirely separate
color designation from red, with the “separation line” between
pink sapphire and ruby precisely defined. Those who adopt this
position argue that a distinct classification of pink sapphire
as an individual variety of corundum is sound, since
designations for other separate categories of sapphire, such
as “orange” and “purple” sapphire, do exist and are necessary.
Color grading.
The need for a universally accepted and practically workable
color grading system for gemstones is obvious and will resolve
many problems including the “ruby or pink sapphire” issue. In
the past, several color grading system have been introduced,
consisted from a series of “master” reference points -in the
form of a set of color chips, or chart of color samples, or a
tri-dimensional substance that silulates a gemstone. However,
in practice, they never meet the strict criteria of proper
gemstone color grading.
It is the author’s opinion that, the color-grading problem may
be solved using C.I.E. chromaticity coordinates emanating from
spectrophotometer readings. Representing the tristimulus
values of the visible color spectrum, these readings should be
the basis of fabricating a tri-dimensional object that will
simulate a “reference-point gemstone” that may be called
master. These masters shall be fabricated from suitable
material taken into consideration transparency, luster,
refractive index, fluorescence and all other appearance
attributes characteristic to ruby and pink sapphires. Since it
is impossible to produce all the colors of ruby and sapphire,
the best method is to fabricate sufficient number of masters
that represent the most frequently occurring colors and
appearance in ruby/sapphire based on their country of origin.
Thus, direct comparison between the color of the gem and the
“master” is possible. Series of these “masters” may consist of
a so-called “color matching system”. Certain number of these
“masters” may represent a range designated as an individual
variety (pink sapphire) of corundum, while other masters may
represent the ruby designation. There should be a “master”
that would represent the “transition point” - that is, the
cut-off point that separates pink sapphire from ruby. Thus,
pink sapphire may be defined as having less that 50% of the
color component needed for a gemstone to qualify as ruby.
Lighting conditions.
Equally important, is the need for a standardized and
universally accepted light source. The apparent color of
rubies and pink sapphires is, to some degree, influenced by
fluorescence stimulated by ultra-violet rays of sunlight.
Thus, rubies and pink sapphires appear different in Southeast
Asia from how they do in locations in the Northern Hemisphere,
say New York or London. But, in reality, to persuade Sri
Lankan and Thai dealers to use a designated light source will
be a nearly impossible task. A suitable light source for
proper color grading should have the following spectral
properties:
Color Temperature above 5,500oK
Color Rendering Index (CRI) above 90
Harmonic spectral distribution in the ultraviolet and
visible region of the e-m spectrum.
There are several lamps readily available in the market that
meet above criteria. Try the 18" long “Vitalite” by DuroTest
Company, or “Daylight-99” by Mitsubishi.
NOTE: Please refer to page 19-20 of my book “The Heat
Treatment of Ruby & Sapphire” for full discussion on lighting
sources.
The effect of heat-treatment.
A final comment on this issue should center on the effect of
heat-treatment on pink sapphires and rubies. The author has
successfully performed many experiments on removing the purple
and brownish-overcast color from rubies and pink sapphires.
The results were very interesting, especially when the color
fell on or about the transition point: On some rubies, the
removal of purplishness produces a purer, lighter-red
coloration that prevents the substance from being considered
ruby any longer, but it appears as pink sapphire. The paradox
was that although the value of the ruby should have being
increased as a result of the removal of the undesirable
brownish tinge, its actual value may be decreased (or remained
the same), because the stone is considered by many dealers as
pink sapphire.
Since problems like this persist, the author wishes to salute
organizations, as well as various individuals in the
gemological community, who actively raise questions about the
whole issue and seek to provide solutions. So far,
unfortunately, apathy on the part of various trade, jewelry,
and educational organizations blocks a sound solution from
being accepted.
Yet, the issue does need to be resolved. With prices of
gemstones escalating rapidly, the game of “buying pink
sapphire and selling it as ruby” needs immediate attention.
(The same game could easily occur with other gemstones as
well: “buy it as green beryl; sell it as emerald.”) If a cure
is ever finally offered by the jewelry industry, I simply hope
that the solution chosen won’t ultimately be worse than the
“disease” itself!
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