Stability: Heat can damage emeralds, especially by extending existing fractures. Light and chemicals can cause the oils, resins, and polymers used to fill surface-reaching fractures to alter in appearance or deteriorate.
Cleaning: Some estimates state that 90 percent or more of emeralds are fracture-filled. Since the great majority of fashioned natural emeralds contain filled fractures, it’s risky to clean them ultrasonically or with steam. Ultrasonic vibrations can weaken already-fractured stones, and hot steam can cause oil or unhardened resin to sweat out of fractures. Using warm, soapy water coupled with gentle scrubbing is the safest way to clean emeralds.
Sources: Afghanistan, Brazil, Colombia, Pakistan, Zambia, and Zimbabwe.