Oxidation is a a process which creates the blackened or antiqued appearance on silver. Oxidized patina on silver isn't particularly durable to long-term exposure to water (like bathing or swimming) or a lot of scrubbing, as friction is the way to polish silver to shine. Constant exposure to tasks such as hand washing, bathing, swimming, washing dishes, etc., will slowly wear away the oxidized patina leaving a shiny silver finish as silver can be polished by both friction and chemical means. Cleaning sterling silver can also remove oxidized patina applied to the piece, so use caution when cleaning if there is desired oxidized patina. If your jewelry has stones in it, please only use with a cleaner that is labeled as safe for stones as any other cleaner could potentially damage them.