Re: oxidizing copper to make it look age

Brushing the copper sheet with a dilute solution of sulfuric acid [H2SO4] will 
form copper sulfate, the aqua blue tint seen on old copper [due to the action 
of acid rain].

Use gloves and eye protection and adult supervision [if necessary].

Sulphuric acid is available from automotive supply centers as battery acid. 
Start with a dilution of at least five parts water to one acid. 

ALWAYS ADD THE ACID TO THE WATER WITH STIRRING

NEVER ADD WATER TO CONCENTRATED ACID [it could explode in your face]

Brush the solution on and wait a few moments for results. You'll have to 
experiment a bit to get the effect you seek.

To stop the coloration, rinse the acid off with a lot of fresh running water.