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Clean opaque semi-precious stones with mild, soapy water. Do not use an ultrasonic cleaning machine; it may alter the color. -- In Style Magazine, July 1999
Guru's note: Ultrasonic machines can not only alter color of gems, but can drastically damage them as well. Some gems will shatter or crack when subjected to the high frequencies that ultrasonic machines produce. It is a good rule of thumb to avoid them with most gem beads, to avoid any unnecessary structural damage.