Enamel is finely ground glass which is fused onto copper at very high temperatures. Enamel is generally very strong but care should be taken to ensure against chipping the edges.   Dropping the piece or being excessively rough with it can lead to small chips and cracks in the surface.   

I use sterling silver for all my ear wires and chains, sterling silver tarnishes over time if not worn and not kept in a dry place away from moisture. If there is some tarnishing, a quick buff with a silver polishing cloth will restore the shine.