Today, combining glass and metal is still the design used in almost all modern mirrors. Mirrors made by coating flat glass with silver or gold foil dates from Roman times and the inventor is unknown.
Definition of a MirrorThe definition of a mirror is a reflecting surface that forms an image of an object when light rays coming from that object fall upon the surface.
Types of MirrorA plane mirror which is flat, reflects light without changing the image. A convex mirror looks like an upside-down bowl, in a convex mirror objects look bigger in the center. In a concave mirror which has a bowl shape, objects look smaller in the center. The concave parabolic mirror is the principal element of a reflecting telescope.
Two-way MirrorsThe two-way mirror was originally called the "transparent mirror". The first US patent goes to Emil Bloch, a subject of the Emperor of Russia residing at Cincinnati, Ohio -- U.S. patent No.720,877, dated February 17th 1903.
Just like a regular mirror there is a silver coating on the glass of a two-way mirror which when applied to the back of the glass renders the glass opaque and reflective on it's face under ordinary light conditions. But unlike a regular mirror, a two-way mirror is transparent when strong light is flashed in the rear.