S990 Sterling Silver jewelries: its silver content is less than 990‰. Marking: S990 or 990.
S925 Silver is pure silver content at 925‰ and added with 75‰ copper. Marking: S925 or 925. It iscommonly recognized as the Sterling Silver. Now 925 Sterling Silver is usually plated with platinum toprevent silver becoming yellow or black out of sulfuration.
      White alloy: it is made of other metal but surficially plated with silver to deceive customers. Whenbeing appraised by authority, only the surface is appraised. As a result, it is appraised as 999 Sterling Silver or 925 Sterling Silver judging from theplating only.