Bronze.

Hint 1 of 7:

The green quarterstaff.

Hint 2 of 7:

A very useful rod.  What have you found that is bronze?

Hint 3 of 7:

Where did you get this rod?

Hint 4 of 7:

From Madame Sosotris.

Hint 5 of 7:

What was the clue to help you get this rod?

Hint 6 of 7:

The mural.

Hint 7 of 7:

Look at the Mural.  It has a bronze frame.