Plasma cleaning of old Indian coin in H2-Ar atmosphere

Cleaning of old metallic coins and artifacts is done to reveal the details which otherwise are buried under a tarnished and soiled surface. A tarnished Indian coin (25 Naye Paise 1960) was cleaned in H2-Ar plasma to improve the surface details and to bring back the metallic shine. The plasma treatment was performed in an evacuated reactor with an RF powered stage with a maximum power of 50 W. The original tarnished old coin became shiny and brighter after treatment in the plasma for a few hours. To understand the plasma cleaning process, various process parameters such as reactor pressure, gas flow rates and stage temperature characteristics have been studied. The ideal plasma cleaning can be achieved with 50% H2 in the pressure range of 20-100 mTorr.