The answer to the question of whether or not jewelry cleaner is harmful for jewelry is largely dependent on the type of cleaner involved, and the type of jewelry involved. Some jewelry can be safely cleaned with a wide variety of substances, while other types of jewelry are more fragile, and harsh cleaners could damage them. Before using a jewelry cleaner, it is important to know which materials have been used in your jewelry.
There are a number of types of jewelry cleaner available. Commercial products are often best, because they include specific usage recommendations and warnings. It is also possible to use an ultrasonic jewelry cleaner, which removes dirt and grime with sound waves. Many jewelers use ultrasonic cleaners, and small models are available for home use. Some people use mild soaps on their jewelry, or gentle abrasives like baking soda, along with homemade cleaners like seltzer tablets and soda, which are generally not recommended because they can stain or crack jewelry.
Certain stones need to be handled very carefully. Opals, pearls, and emeralds are all very fragile, for example, and they can break or splinter easily. Ultrasonic cleaning and harsh cleaners are not recommended for these materials. Harder stones can withstand harsher cleaners: diamonds, for example, will endure anything you throw at them, except another diamond. A packaged jewelry cleaner usually indicates which stones it can be safely used with.
Metals are also of issue. Silver tarnishes and films easily, so using soap or an acidic cleaner can be a very bad idea, as the cleaner may leave a residue or encourage tarnish. Gold is very soft, so abrasive cleaners should be avoided with gold. Platinum tends to be hardier, withstanding a wider range of cleaners. It's best to find a jewelry cleaner which is labeled as safe for use on the metal used in your jewelry, to ensure that the metal will not be damaged.
Handling jewelry carefully during the cleaning process is also important. Some stones may crack if they are jarred in their settings, especially if they have been heated, and others break down if they are frequently exposed to sunlight, becoming very fragile with repeated wear. Others, such as opals, do not appreciate getting wet, and they may cloud or dull when exposed to water.
If you aren't sure about the materials used in your jewelry, you may want to avoid using a jewelry cleaner. Use a soft cloth to gently buff the jewelry and stones, and if the jewelry is badly soiled, consider taking it to a professional who can assess the situation and determine the best course of action and cleaner to use. You can also ask a jeweler for cleaning recommendations to ensure that your jewelry endures to be enjoyed for decades.