The safest everyday cleaning method for many durable gemstones is modest: lukewarm water, a small amount of mild soap and a soft brush. Rinse carefully and dry with a lint-free cloth. Always clean over a bowl rather than an open drain.
Hardness describes resistance to scratching, not resistance to impact. A hard gemstone can still chip at a thin girdle or pointed corner. Remove jewellery before heavy work, sport or any activity where a stone may receive a sharp blow.
Ultrasonic and steam cleaners are not universal solutions. Fracture-filled stones, heavily included gems, emeralds with oil treatment and assembled materials may be damaged by heat or vibration. When treatment history is uncertain, choose gentle hand cleaning and ask a qualified jeweller.
Storage matters too. Keep pieces separated so harder stones do not scratch softer gems or metal. Periodically inspect prongs and bezels for movement. A thoughtful routine is less dramatic than a restoration, and far more effective.