C752 18% Nickel SIlver Sheet 1/8″ x 6″ x 6″ .125″ (3.1 mm) slightly tarnished
It is nickel silver, which is a copper and nickel alloy, C752. This was sold as material to make guards, bolsters and decorative pieces out of. I would imagine that in any of those uses the tarnish would easily remove during normal shaping and would not cause any issues with the final product.