Play of Color @ Jewel Info 4 UBy: Nasrina Parvin Khan
Summary: A well-known Play-of-color gemstone is opal. Opal is an amorphous from of silica (sio2, nh2o). It is made up of sub microscopic spheres of silica with a little amount of water and air trapped in the spaces between these round spheres.
What is Play-of-color?
Play-of-color is a unique special
optical phenomenon. This phenomenon
is usually exhibits by the gem opal.
The iridescent color effect in opal
described as Play-of-color. Color of
rainbow can be seen in gems by this
optical phenomenon. But the
displayed colors are unrelated to
the gem's own body color. So, we can
guess that the structural pattern of
gem is responsible for this colors
creating optical phenomenon. Due to
the structural pattern the light
interfere or diffract in gems and
produce the color phenomenon named
as Play-of-color.
Play of color in Opal
A well-known Play-of-color gemstone
is opal. Opal is an amorphous from
of silica (sio2, nh2o). It is made
up of sub microscopic spheres of
silica with a little amount of water
and air trapped in the spaces
between these round spheres. The
amount of water in opal may be 3% to
21%. But the precious opals have 6%
to 10% water content usually.
Opal is a sedimentary stone. In the
time of formation of this stone,
oozing water through the earth
dissolved in silicates and become
rich. The silicates are deposits as
minute spheres when the water enters
in a cavity.
The transparent spheres of amorphous
silica and the voids between them
form a 3D grating. This structural
pattern is the reason of
interference and diffraction of
light from the surface or the
interior of gems. This property
helps to display multiple colors as
the angle of incident light changes.
The openings act as the diffracting
gratings, which split the light into
colors, and the layered structure
creates interference. The passing
light through the stone breaks into
various colors. So, we can say
diffraction of light take place by
layers of silica spheres in its
composition and it is responsible
for the phenomenon play-of-color.
Shifting patches of spectral colors
seen on the surface or in the
interior of gem due to the
phenomenon play-of-color. Reflected
lights from different layers of
silicon slightly overlap from sync
waves and help certain spectral
colors to decrease or remove and
reinforce others. So, we get a group
of shifting colors that have a
trembling on and off effect. The
patches of colors moved when the gem
is turned around. The effect just
like to a bubble with rainbow color,
just more dramatic.
Large openings between the spheres
do not allowed the light to bend
when passing through them. That is
why no diffraction takes place and
we get common opal. Random shape and
arrangement of spheres also produced
common opal. Shape, size and
regularity of the spheres influenced
the colors seen. It also depends on
the angle of view. Uniform shape and
size of spheres diffract light and
help to produce precious opal. On
the other hand, smaller size of
spheres helps to see more blue and
violet colors. But the spheres must
be smaller than 1500 angstroms. More
reds and oranges are seen with
bigger sized spheres. But the
spheres should not be larger than
3500 angstroms.
Name Origin
Opal gets the name for its special
optical phenomenon Play-of-color.
The name came from Greek word 'opallus',
which means to see a change in
color.
The quality of opal justified by the
number of color exhibited by the
gems.
The most valuable opal is
'black-opal'. Which has a strong
play-of-color. Different types of
colors flashed brilliantly by this
stone. Due to dark background color
it has given the name 'black opal'.
The colors of black opals are black,
dark green, dark brown and others.
These gems are transparent to
translucent.
There can be seen many other opals,
like white opal, crystal opal, fine
opal, cherry, water opal and etc.
White opal is transparent to opaque.
It has white background with
Play-of-color.
Crystal opal has no background color
with strong play-of-color. This
stone is transparent to translucent
and lets the light pass through it
unlike others.
Fire opal is also transparent with
yellow, orange, red or brown
background color. It may have
play-of-color or not. Fire opal with
red background color is also known
as cherry opal.
Water opal is transparent to
semitransparent with colorless
background. It has little or
Play-of-color.
The point of color seen in opal due
to the Play-of-color is called as
"fire".
The term 'flash' used to refer
sudden play-of color as stone moved.
Gemologists divided the phenomenon
play-of-color in various types, like
pinfire, mosaic, flame, peacock etc.
A minute, close-set flash of color
is called as pinfire. A large,
regular, angular, close-set flash of
colors is known as mosaic. Sweeping
reddish bands across the gem is
called flame, whereas blue and green
color effect is known as peacock.
See Also:
Color Effects
in Gems ,
Asterism,
Chatoyancy
External Reference
Play of color info in gemsociety.org
Color Effects in gems
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