Silver mirror 20 mm bevelled along the circuit.
Links[1] http://dubielvitrum.pl/sites/default/files/styles/duze_800/public/agis_0218.jpg?itok=sVvlxXtV [2] http://dubielvitrum.pl/sites/default/files/styles/duze_800/public/bd_2.jpg?itok=rXmxqOui