Sterling silver is formed when combining pure silver with copper. Sterling silver jewelry has a 925 stamp, meaning that the composition contains 92.5% silver. It is in violation of Federal Trade Commission policy (§23.6.b) to stamp jewelry 925 if it is not entirely 92.5% silver (selling jewelry stamped 925 on sterling silver plated base jewelry is illegal in the United States). Sterling silver improves the jewelry's durability and delays tarnish. Silver should not come into contact with harsh household chemicals such as bleach, ammonia, or chlorine as it may react with the silver and turn it black. To avoid scratches, store sterling silver in a jewelry box. To prevent tarnish, keep sterling silver jewelry in an airtight wrapping, such as a plastic bag, when not in use. Use a polish cloth to remove tarnish.