Circular Mirror, approx. 32 cm diameter (Chaddesden DE21)

I have a circular mirror, approx. 42 cm diameter and 4 mm thick. It looks as if it was stuck to a wall or timber once, as there are the remains of sticky pads on the back.

There is a scratch in the backing of about 2 cm towards one side (as can be seen in the 2nd photo) and some of the silvering is missing around one edge (see photo 3).