Answers

2016-03-15T23:10:57+05:30
Oxidation happened. It can be removed by infrasound cleaning, where it is placed in a cleaning solution and infrasonic waves are passed which removed the dirt.
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2016-03-17T18:33:20+05:30
The silver reacts with oxygen and a new layer is formed due to this. this process is called oxidation.
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