Why a metallic mirror temperature cannot be read by a thermal camera? When I look at a first surface mirror with a thermal camera I don't see the temperature of the mirror but the temperature of the reflected objects. It is like if a polished metallic surface don't lose infrared light due to is own thermal agitation. Whatever the temperature of the mirror ( without being altered ), I can still measure the temperature of the reflected objects accurately. How does it works ? Why a smooth metallic surface don't lose energy by IR radiations ?
 A: An interesting consequence of thermal equilibrium is that objects that don't absorb much thermal radiation also don't emit much thermal radiation. If you put two objects, one black and one white, in an isolated box and let them reach thermal equilibrium (same temperature), the black object will emit much more radiation but will also absorb much more radiation than the white one. This is why non-contact thermometers work best with black surfaces.
A polished metallic surface may not be a very good emitter of thermal radiation. So when viewed with a thermal camera, the reflection of other objects by the mirror may overwhelm the mirror's own emission.
It's not that the mirror is not emitting any radiation. It's just that the radiation emitted by other objects is much stronger.
A: I would imagine that it is because light is a form of electromagnetism, as in, the infrared light the camera is detecting is the light being reflected off of the mirror, as the mirror's personally emitted temperature is simply a reflection of the thermal agitation of the object it is reflecting.
