First mirrors will be the plasma facing components of optical diagnostic systems in ITER. Mirror surfaces will undergo modification caused by erosion and re-deposition processes. As a consequence, the mirror performance may be changed and may deteriorate. In the divertor region it may also be obscured by deposition. The limited access to in-vessel components of ITER calls for testing the mirror materials in present day devices in order to gather information on the material damage and degradation of the mirror performance, i.e. reflectivity. A dedicated experimental programme, First Mirror Test (FMT), has been initiated at the JET tokamak and also at other controlled fusion devices: TEXTOR and Tore Supra.