Reflective. Or silver? I guess? Depends on the make/material and whether or not it uses liquid mercury for the reflective substance if it's glass containing a fluid. Riddle me this, It binds us together, exists neither here nor there, Everywhere! All encompassing! Can be warm, can be cold! Gentle or harsh, used by many, then very few. It's power is great, It's misuse terrible. What is it?