Why Can't Brass Rods Be Charged by Rubbing?

[perjogab]

Hey guys, I have a physics exam tomorrow. I found a question that I can't solve.

Rubbing a polythene rod with a cloth makes the polythene negatively charged but rubbing a brass rod in this way will not charge it. Why can't the brass rod be charged this way?

Thanks

 

[turin]

Would you consider brass to be a conductor or an insulator?

 

[perjogab]

Brass is a conductor isn't it?