Surface Defects Analysis and Anti-Tarnish Technology for Silver Coins
Min Huang · Materiais Protection · 2002
The surface defects of silver coins were analyzed to find out the reason and put forward protective method as coatings. The protection method with multiplayer build\|up film, namely electrolytic passivation combined with dipping anti\|tarnish agent, was developed through different anti\|tarnish tests. Results showed that after treating no defects occurred on the silver coins about 6 months under normal conditions. Corrosion resisting time of treating silver coins was 150 min in 3 mg/L hydrogen sulfide gas at 40 ℃ and almost 10 times longer than that without treating. Else the time reached 130 min in 3% potassium sulfide solution at room temperature and was 26 times of that without using anti\|tarnish technique.