On 2 Feb, 12:08, "robgraham" wrote:
http://www.mirrorresilvering.com/a_b...of_mirrors.htm

Silvering with nitric acid is older than Liebig (17th century at
least). As soon as you have access to powerful acids you try to
disssolve precious metals in them. You store the results in glass, as
not much else will hold them. The rest is just observation of what
happens afterwards and applying it as a practical technique. They
probably knew this stuff back in the Hogwarts era.

Amalgam silvering works pretty well (as does fire gilding), but I
don't fancy arranging adequate fume control for something as big as a
mirror.