a mirror material is made of 2 different material, one to cast reflection and another one (a zinc plate to absorb light) so this is my set up for a mirror. u might get away with simpler method, depending on what u want to acheive... so for instance, if u have a primitive cube, u put the zinc plate on a face behind the face containing the mirror shader. p.s. as with a real mirror, if light is casting right in front of it, it will be bright, so ur light source need to be coming from behind it for best results.