One of the
most exciting and interesting gemstones you can buy is one that has
color change, Alexandrite is most recognised of these gemstones as it
has a dramatic color change depending on your light source. Today
there are a lot of color shift gemstones, being sold as color change.
Usually a color change gemstone commands a premium price, so how can
you be sure you are getting color change and not color shift?
All of a
gemstones color (hue, tone and saturation) is dependent on two
things, how the gemstone is cut and the most important component
light. It is the type of light and direction of the light that
produces the brilliance and fire in a well-cut diamond or the
beautiful color in gemstones.
The color you
see in a gemstone is the result of the light that returns to your
eyes after bouncing off the gemstones crystal structure. Now we know
what causes color but what makes it a color change or color shift gemstone?
chromium that allows equal amounts of red and green light to pass
through it causes color change in Alexandrite. Because of this
balance of red and green, if you view Alexandrite under incandescent
light (rich in red) the gemstone looks like a red Ruby.
If you then take the gemstone and hold it under an incandescent
light (rich in blue/green) the Alexandrite looks more like an Emerald
Green. This is color change.
Color shift is
representative of colors that can change in the different or the same
light source, a good example of this would be Tanzanite that will
shift from blue to violet/purple by tilting the gemstone in the same
light source. You will find a reasonable amount of gemstones will
have this effect especially the ones with rich colors,
explanation of the difference I have used for deciding what is color
change and what is color shift, is for those that have seen or have
access to color grading wheel which is a chart that designates all of
the colors of gemstones for grading gemstones. GIA calls it the hue
wheel and it shows all of the color hues from Blue,
to Orange, to Red,
to Purple, to
Violet (32 hues in all). If a color change moves from Red to the next
color on the wheel (orange) then this is called a Color Shift. If the
color moves from Red to Green, which is on the other side of the
wheel, then this is called Color Change.
Some of the
major natural Color Change gemstones are Sapphire,
Alexandrite, Spinel, and Garnet.
Also be aware,
today there are a lot of coated or diffused gemstones that will also
show color change.