The qualities associated with metal are firmness, rigidity, persistence, strength and determination. The metal person is controlling, ambitious, forceful and set in their ways as metal is very strong; and they are self-reliant and prefer to handle their problems alone. The metal person is also materialistic, business oriented and good at organization and stability. However the metal person can also appreciate luxury and enjoy the good things in life. Just as metal can conduct electricity, the Metal person has strong impulses and generative powers and can bring about changes and transformations for those who come into contact with them. Metal governs the Lung and the Large intestine, nose and skin. The negative emotion associated with metal is grief, while the positive emotion is courage.

Seems to me any 'evocating' you try to pull with metal should be a block/shield.    Though you could make a nice argument for lightning bolts.

http://en.wikipedia.org/wiki/Five_elements_(Chinese)