Kelsier had only burned the four physical metals. Reluctantly, he burned the others.  Gemmel  nodded;  now  that  Kelsier  was  burning  copper,  all  signs  of  his  Allomancy would have vanished to the other man. Copper, what a useful metal — it hid you from other Allomancers, and made you immune to their emotional Allomancy.

Some spoke of copper derogatorily. You couldn’t use it to fight; you couldn’t change things with it. But Kelsier had always envied his friend Trap, who was a copper Misting. It was a powerful thing to know that your emotions were not the result of outside tampering.

Of course, with copper burning, that meant he had to admit that everything he felt — the pain, the anger, and even the numbness — belonged to him alone