Ultrasonic: Usually safe.
Heat: Poor; color change may occur with heat.
Chemicals that harm: Hydrofluoric acid, ammonium fluoride.
Clean amethysts with warm, soapy water and a soft brush or an ultrasonic cleaner. Amethyst Rings can become paler if it is out in the sun or under heat.
Keep amethyst jewelry in a fabric-lined box and to keep other pieces from scratching it. With these tips, your amethyst should last you for many years.