… The mirror does not reflect anything. You can see neither the surrounding things nor yourself in it. What you see in the mirror is illusion, ghost, and your twin. The person who looks at you from its golden surface is not you. This is a copy of the mask you wear to be recognized by other imaginary characters.
The mirror is not intended to show things already known. It shows things you do not know yet.

The novel: 
Venetian Glass Magic