When was the first plate glass mirror made?
It can be presumed that the word “plate” is referring to the degree of uniformity delivered by the float glass process. The first automated plate glass was made in 1848 by Henry Bessemer using a roller process. Uniformity was produced by grinding, as opposed to inherent material forces as occurs in modern float glass processes. If we presume that anything made prior to this time would suit the definition of ‘plate’ glass, then mirrors could not have occurred much sooner than this time.
