Tourmaline, the saturation success story of the 20th century. Discovered
in 1989, and mined out by 1990, here is a gem that has escalated
in price from several hundred to tens of thousands of dollars in
a single decade. The key to understanding this dizzying increase
in price is to be found in Paraiba’s verbal description---“neon”
or “electric blue”. Few gemstones achieve the intense
saturation of Paraiba tourmaline. Perhaps the only contender, Burma
Ruby, not surprisingly sells for a similar price.
Unfortunately natural things rarely come in visually
pure hues. For this reason connoisseurs divide hue into primary,
secondary and sometimes tertiary components. For example, a ruby
is never pure red; it is either violetish, pinkish or orangish red.
The ish refers to the secondary or modifying hue. Secondary
hues are also pure spectral hues or modified spectral hues such
as purple and pink.
This approach to grading borrows liberally from
The American Gemological Laboratory’s Colorscan grading system.
The Colorscan system works well because it treats the non-spectral
hues gray and brown not as hues, but as saturation modifiers or
masks; the presence of either acts to dull and muddy, that is, to
reduce the saturation of those hues that are present.
Among the fine points of connoisseurship in gemstones
is the question of preferred secondary hues. Is a pinkish ruby preferable
to a violetish ruby? This is a question that is often asked but
seldom answered. In the December issue of JCK, Gary Roskin identifies
pink as the preferred secondary hue in ruby2
. This is a courageous call, and Roskin deserves credit for having
the intestinal fortitude to render an opinion. Unfortunately, I
believe his conclusions are the wrong ones! Let’s see if an
analysis of this issue can clarify a few of the points made so far.
Running the Gamut:
The hue we call pink is simply the name given
to light-toned red. As with most gemstones, a pure spectral hue
is preferred. That is to say the ideal color in ruby is red--the
brightest, richest, purist red possible. Red reaches its optimal
saturation at about 80%, a rather dark tone. When we talk about
pinkish red we are talking about a secondary hue that is, by definition,
a light-toned modified spectral hue, in short--a light-toned red.
In ruby a preferred secondary hue is, or shou be, one that does
not dilute, but rather reinforces the primary hue. In this case
a light tone added to a dark tone dilutes the latter--reducing the
color saturation below its optimum gamut.
This is not to say that a pinkish-red ruby isn’t
beautiful. My wife has a piece I made containing a highly UV florescent
pinkish red three-quarter carat Vietnamese stone that is visible
across a crowded room. Lighter toned ruby, particularly florescent
stones, sizzle like beef fat on a hot grill! Also, if one wishes
to appeal to authority, the 15.97 carat Caplan ruby, the most expensive
ruby sold to date, is a visibly pinkish gem3
However in ruby, pink is the least desirable of
the possible secondary hues. Which is the most desirable? We are
left with orange and blue. Notice I didn’t mention violet
or purple. A ruby can be either, visually, but the appearance is
caused by blue mixing with the primary red, which produces either
a purplish or violetish hue, depending upon the strength of the
blue. Remembering the spectral hues--purple is a hue-modified spectral
hue falling halfway between red and blue; violet is a hue halfway
between purple and blue. Thus violet is further from red on the
color wheel than is purple. Whether the ruby seems purplish or violetish
depends completely on the strength of the blue secondary. Given
that the ideal is a pure red, and purple is closer to red, less
is more--purple would naturally be the preferred secondary hue.
“Asking to see the pigeon’s blood
is like asking to see the face of God”.
Anonymous Burmese trader
On a trip to Moguk reported in this publication
I saw a few natural slightly purplish “pigeon’s blood”
rubies. Because the optimum saturation/tone gamut for purple is,
at 80% tone, just slightly darker than red, the purplish secondary
hue visually reinforced and richened the red primary hue.
This leaves us to consider orange. Orange as a
secondary hue is rarely found in Burma-type ruby. It is much more
characteristic of ruby from Thailand which is formed in the iron-rich
soils of Chantaburi and Trat provinces in the central part of the
country. Thai rubies tend to be dark in tone with a dark gray mask
that visibly dulls the red primary hue. Orange is a spectral color
that achieves its optimum saturation at fairly light tonal levels,
perhaps 30%. Thus a bit of orange will tend to lighten, and to some
degree, brighten the overall tone.
At darker tonal levels orange becomes increasingly
brownish. In fact there is really no such thing as dark orange--darker
toned orange is simply brown. Brown ”muddies” the red
primary hue, thus reducing its saturation. This is the reason why,
with the discovery of a new source of Burma ruby at Mong Hsu, Thai
ruby all but disappeared off the radar screen. Thai ruby is often
of a purer red primary hue than the Burma type, but the addition
of brown so reduces the saturation that the stone appears dull as
dirt when compared to gems from Burma.