polished vs oxidised

Asymmetrical necklace L06 from Fast Forward ⏩
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Just like all our designs of this collection, the necklace contains two pieces of the same metal.
They appear different though.
Left and right parts are silver, but while the left is simply polished, the right part of the necklace is oxidised silver.
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Did you know it's both silver?
Of what material did you think it is?