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Copper washer brightening after heat treatment

We annealed copper sheets. It looked discoloured or it has lost its brightness. How can we get the same brightness again.

MADHU MAHESWARAN
an electronics company - COIMBATORE , TAMILNADU, India
2003

You need an oxidizing acid of some sort. There are many, based on nitric acid, chromic acid, and others but the safest is probably a proprietary mix of sulfuric acid and stabilized hydrogen peroxide.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2003

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