"How does gold /gold plating help?" 

  Gold (Au) plating has several functions which include providing corrosion and tarnish resistant layer 
  and an aesthetically beautiful appearance.

  Electroplating is used to deposit a barrier metal, nickel, on a copper base which prevents the copper 
  tarnishing the gold. It also provides an improved mechanical backing for better wear resistance. Bright 
  hard gold circa. 99.7-99.9% purity with knoops hardness 120-300 is then plated on top of the nickel.