"Over time, silver will tarnish or turn black. This is due to a chemical reaction between the sterling silver and oxygen in the air. Silver itself doesn't react w/ oxygen but alloys in the sterling silver, such as copper, do react with the oxygen in the air thus turning it black. Climate is a major factor in just how fast sterling silver will tarnish. The more humid the climate, the faster it will tarnish. Other problems can also arise with sterling silver. Sodium Chloride (NaCl) or common table salt is very corrosive to the silver-copper alloy, which is what sterling silver is. The corrosion needs to be removed to bring back the origional beauty and luster back to the sterling silver."
