Brass and sterling silver will oxidize over time.  If a non-oxidized finish is preferred, the jewelry can be wiped with a polishing cloth or gently scrubbed with baking soda, water, and an old toothbrush.  To retain the finish of an oxidized silver piece, cleaning is not recommended as it will remove the finish.  Gold and gold filled jewelry can be cleaned by soaking in white vinegar for 15 minutes, then scrubbed lightly with a toothbrush if needed.  It is best to store jewelry in a sealed plastic bag. Earring backs may stretch over time. To keep ear nuts secure and strong, occasionally give them a light squeeze before attaching them to the earrings.