The more durable gemstones, such as sapphires, rubies, garnets, and amethysts, are more resistant to scratching and can withstand at-home solvents and ultrasonic cleaning machines, which use water and high-frequency ultrasound waves. Helena Kroedel, a spokesperson for the Jewelry Information Center, a nonprofit trade association in New York City, recommends Brilliant ($6, www.brilliantdiamondcleaner.com for locations), a spray-on cleaner that is safe for most stones and can dissolve the lotion and dirt that dull jewelry. However, if you have any do-it-yourself reservations, consult a reputable jeweler.

Gems with more delicate natures, such as opals, peridots, topazes, and aquamarines, can crack or chip if cleaned in an ultrasonic machine. Stones that have undergone waxing and oiling treatments to enhance their quality, like turquoise and emeralds, are more likely to dull if cleaned incorrectly. Instead, gently wash these sensitive varieties with a soft toothbrush, lukewarm water, and a mild cleanser, like Ivory dish soap. And thorough drying is a must, especially when cleaning gems that are set in sterling silver, which can tarnish with extended exposure to moisture.