If a gold product has the hallmark '375,' it signifies the gold is 9 karats (or 37.5% pure). The remaining 62.5 percent is an alloy of other metals, such as nickel, copper, or, in certain circumstances, silver. Products stamped with a lower quality mark may still be of good quality, but they are not sterling silver. Sterling silver can be divided into three levels of purity: sterling silver A, B, and C. Silver products marked with the hallmarks "925" or "999" must be 100 percent silver. Those that are 95 percent silver can be labeled as sterling silver A. Sterling silver B products contain 90 percent silver; sterling silver C, 89 percent silver. Gold products must be stored in a cool, dry place out of direct sunlight. Gold jewelry should never be worn if it is uncomfortable to wear. Wearing ill-fitting or too heavy of an article of gold jewelry could cause you pain if you suffer from arthritis or other joint problems. Jewelers often use the word "sterling" to describe silver items that are all of equal quality. But there are different qualities of sterling silver, so "sterling" does not always mean what you think it means. Only silver with the hallmarks "925" or "999" can be called sterling silver.