Humans and our ancestors probably used pools of still water as mirrors for hundreds of thousands or even millions of years. Later, mirrors of polished metal or obsidian (volcanic glass) gave wealthy preeners a more portable view of themselves.
The mirror as we know it, however, came about surprisingly early. Who was it, then, that first discovered that a sheet of glass, when backed with metal, becomes a perfect reflecting surface?
As far as we know, the first mirror-makers lived near the city of Sidon, Lebanon, some 2,400 years ago.
Since glass itself likely was invented in Lebanon, it's not too surprising that it was the site of the earliest modern mirrors. Unfortunately, we do not know the name of the tinkerer who first came up with this invention.
To make a mirror, pre-Christian Lebanese blew a thin sphere of molten glass into a bubble, and then poured hot lead into the bulb of glass. The lead coated the inside of the glass. When the glass cooled, it was broken and cut into convex pieces of mirror.
These early experiments in the art were not flat, so they must have been a bit like fun-house mirrors. (Users' noses probably looked enormous!) In addition, early glass was generally bubbly and discolored.
Nonetheless, the images would have been much clearer than those obtained by looking into a sheet of polished copper or bronze. The bubbles of glass used were thin, minimizing the impact of the flaws, so these early glass mirrors were a definite improvement.
This wonderful new technology quickly spread throughout the Roman Empire; mirrors were used not only for self-admiration, but also for magical amulets.
After all, there's nothing like a clear glass mirror to repel the evil eye!
For much more information on mirrors, as well as many other interesting topics, see Mark Pendergrast's book Mirror Mirror: A History of the Human Love Affair with Reflection, (Basic Books, 2004).