[header] How to oxidize copper [title] Hard boil two or more eggs. [step] Two or three eggs should be plenty unless you have a large amount of copper to oxidize. Place them with their shells intact in a pot of water and bring to a boil for at least ten minutes. 
Don't worry about over-boiling them. In fact, that over-done greenish ring and sulfur smell is exactly what you need, since the sulfur will alter the appearance of your copper.