Habe eben gefunden, darf ich doch von Euch nicht vorenthalten:
Eva hat schon beschrieben, ich denke dies ist die selbe, eben aber mit Bilder immer einfacher:

How to oxidize with a boiled egg? This technique works with not only silver but silver plated and copper wire too 🙂
Additional info: the idea is not mine, saw on the internet, but haven't found any detailed tutorial about it 🙂 + i don't think you should eat the egg after using it for this 😀

** you do not have permission to see this link **

Viel spass dabei!