Tarnish is a natural process for ANY real sterling silver or gold.  How much or how fast your sterling or gold collar and lock will tarnish depends on many factors like your body's chemistry as well as environment (air, water, chemicals).  Things like hair products, perfumes, smoke, your area's air, can all contribute to tarnish.  How fast it tarnishes depends on the severity of the culprit.   Some perfumes and hair products can tarnish your jewelry in seconds.  Other things like salty air or if you have a high concentration of sulfur in the air, can tarnish your jewelry in just a few days or faster.