Rubies
that are beautiful in their original
crystal form are extremely rare.
To satisfy the demand for beautiful
rubies, crystals have long been heat-treated
to remove blackish or bluish colors
and bring out their beauty. Recent
advances in heat-treatment technology
have dramatically increased supply,
making affordable prices a reality.
However, the high-temperature treatment
(1,600 -1,900C
/2,910-3,450F)
of rubies has resulted in diminished
durability,
giving rise to problems such as a
loss of consumer confidence in the
material.
Rubies from the historical
Mogok district, and from the Mong
Hsu mines that began production in
the late 1980s, are representative
of the material from Myanmar. Rough
stones from these areas are taken
to Thailand for heat treatment and
subsequent polishing. However, not
all of these rubies are heated. Gems
that are inherently beautiful, with
few defects, do not require treatment.
The ruby as shown in the photograph
on the next page is
an untreated ruby from Mogok. It
is a superb piece
with high transparency and brilliance,
weighing 5.46 carats. At a tone level
of 6, it displays a well-balanced
mosaic pattern and a red, flame-like
color. Small rubies weighing less
than 0.1 carat often appear to lose
their brightness at tone level 6. |
This is
because each point in the mosaic
pattern becomes so small that the
contrast between them is lost. Any
small stone, not just ruby, will
generally be better suited for jewelry
use if its color is slightly lighter
in tone. Professional jewelers know
from experience that ideal tone levels
change with the size of a stone.
Evaluation of the color tone also
differs between generations, nationalities,
and how the gems are used. Rubies
with a tone level of 4 and beauty
grade of S or A will have superior
beauty, regardless of size, so it
is likely that such stones will become
increasingly popular, with their
values rising compared to other stones.
Untreated rubies from Mogok are often
quite included, but as long as the
inclusions are not excessive, they
can give a stone a soft beauty. Inclusions
are permissible as long as they do
not detract from beauty or durability.
A well-balanced mosaic pattern of
light and dark shades of red is a
prerequisite for beauty grades S
and A. |
