Changes in color of amethyst by heat treatment and UV radiation. Amethyst is pleochroic when the polarization of the light is changed from parallel to the c-axis to perpendicular to the c-axis, amethyst changes its color from blue-violet to purple. ...

Will amethyst change color?

If you leave your amethyst in sunlight or under other UV sources for too long, its color will fade. And if you expose amethyst to heat, you'll see the color fade as well. Sometimes, instead of gray or clear crystal, you'll end up with vivid yellows that look a lot like citrine.

How do you restore amethyst color?

The colors of both amethyst and smoky quartz are stable to light, but are lost when heated to between 300 and 500°C. If not overheated, the color center and the color can be restored by another irradiation, and so on.