CHANGE OF COLOR (COLOR CHANGE) - A phenomenon of some colored stones in which the gem material appears a different color in different types of light.
Change of Color
A phenomenon seen in some gems which have a different color in natural light than in artificial light. The color-change is caused by selective absorption and transmission of light.
Change of Color
Sometimes diamond changes color or appears with a different color in different types of light. This is caused by selective absorption and/or transmission of the specific type of light to which the stone is exposed.
Change of color can occur as a full color change from green to red, or as a color shift from blue to purple.
Alexandrite, a chrysoberyl variety, possesses a distinct change of color when viewed under different (incandescent and fluorescent) light sources. The change in color is caused by trace amounts of chromium and vanadium.
However it does not mean multi-colored but a change of color in a stone due to movement of light through it. Pleochroism is a general term referred to the processes of dichroism and trichorism.
Opal's name evolved from the Roman word opalus from the Greek word opallios - "to see a change of color." The Greek word was a modification of the ancient Indian Sanskrit name for opal, upala, which meant "precious stone.
Patination: (as above) the change of color on the surface of metals, such as bronze and copper, after long exposure to the atmosphere.
One of the world’s most coveted gemstones, opal’s name evolved from the Roman opalus which was derived from the Greek opallios, meaning “to see a change of color.
The name opal was derived from the Sanskrit "Upala" and later the Greek derivative "Opallios," meaning to see a change of color. Opal is a gemstone that ranges from semi-transparent to opaque.
The spessartite-grossular-pyrope color-change garnet exhibits a change of color from "light bluish green" in transmitted fluorescent light to purple in reflected fluorescent light. In incandescent light, the color is "light red to purplish red".
Irradiation techniques bombard the crystal with high-energy radiation (like gamma rays), producing a stone with very little radioactivity and a change of color.
Heating these crystals can cause lightning and a change of color in smoky quartz crystals, sometimes too much more desirable shade. If enough heat is applied the stone be returned to fully colorless condition.
Some color-change sapphires will have only a slight visual change, while others have incredible 100% change of color. The stronger the percentage of the color change, the more expensive the sapphire.
Beware, because the stones from India are often oriented in the wrong direction: To preserve weight from the original crystal, they cut them perpendicularly, so the intensity of color and the change of color is more beautiful looking through the ...
 See also: Stone, Color, Crystal, Jewel, Jewelry
  
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