Gemstones With Change Of Color

To anyone who has ever viewed a fine quality piece of alexandrite, the phenomena of change of color must certainly rank among the greatest wonders of the gem kingdom. Change of color or the alexandrite effect as it is known is a relatively recent discovery. The gem was christened alexandrite, in honor of the future Czar Alexander II on whose birthday it was supposedly found. After its discovery it achieved rapid popularity, not only for its interesting color change, but also because the two colors, green and red, were the colors of the Czarist Russian army. Fine quality alexandrites are today among the most desirable precious stones. Besides the normal criteria for judging gems, the quality of an alexandrite is based primarily on the quality of color change and the intensity and purity of those colors. The best colors would those of a fine emerald or ruby and this stone would be described as having a one hundred percent change. Stones of this quality may be difficult to find, but most specimens show a change of only twenty to thirty percent with the two colors being diluted with brown and yellow.

There are various gemstones which display the phenomenon of change of color. Synthetic alexandrite has been manufactured in Russia, USA and other countries by flux and Czochralski (pulling) process. Both types display a fine change from bluish green to purplish red, just as in the natural stones. The flux grown gem materials show inclusions such as wispy flux fingerprints, platinum plates and crystals and angular zoning. Stones grown by the Czochralski process are usually free of inclusions, but may show gas bubbles and/or curved growth lines.

Of all the gem materials which show a change of color, none is more commonly seen than the synthetic color change (alexandrite-like) sapphire. This material is not synthetic chrysoberyl, but instead is flame fusion synthetic corundum. By adding a trace of vanadium to the growth mixture, a color change is produced. The color is grayish green in daylight and purplish red in incandescent light. Often this gem will be offered for sale as synthetic alexandrite or even worse, as natural alexandrite. The stone is not difficult to identify as the color change is not exactly the same as true alexandrites. Proper examination will reveal curved striae and possibly gas bubbles. Natural color change sapphires do exist and show a change that varies from violetish blue to grayish green in daylight, to purplish red in incandescent light. The change of color can be attributed to vanadium, chromium, iron and titanium in various proportions. Fine quality color change sapphires are prized by collectors.

Next to alexandrite, the stone with the most dramatic change of color is probably the color change garnet. Color change garnets show a change very similar to that of alexandrite from a bluish green to purplish red. Glass imitations have been made to simulate a color change as well. Since the stone does not really change color from one light source to another it should not considered as a true change of color.