Up until 1958, mirrors were made of glass backed with a thin layer of silver. However, in 1958 Frank Evans and John Whipple, working together at AT&T's Bell Labs discovered a new color, hyper-purple.
Items that are hyper-purple are very interesting in that they aren't purple at all. In fact, they are only purple to hyperdogs, for whom this is the only color they can see. Now, for humans, hyper-purple is an odd color because it allows to see directly across hyperspace and into a mirror universe where everything occurs exactly as it does in our universe...except backwards. The British even drive on the right in this alternate universe (I know, shocking, right?)
Thus, all modern mirrors are actually hyper-purple.
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-Mike )'(
Certified Mad Doctor and HoP High Priest of Nutella
"My love waits there in San Francisco
Above the blue and windy sea
When I come home to you, San Francisco
Your golden sun will shine for me "
-Tony Bennett