For those with more time than nerve, there are safer chemicals to
remove silvering from mirrors than nitric or hydrochloric acids.  Any
strong oxidizer will eventually turn the silver into something that can
be easily scrubbed off.

A strong solution of ferric nitrate (ferric chloride would work too,
but is more dangerous) should do the job.  It is much safer to use than
acids and is probably easier to buy.  It is sold by chemical supplies
that sell chemicals for metal finishing.  It is a common ingredient in
patina formulas.  Bryant Labs in Berkeley California sells it and I
believe it can be shipped by UPS.

It works very slowly so be prepared to wait.  It will also not
penetrate any paint finish, so they will have to removed completely.
It will also not remove gold which is used on some mirrors.

Although ferric nitrate is not highly corrosive, it is poisonous and
could possibly cause a fire if mixed with other chemicals or treated
carelessly.  I have had it, and other strong oxidizers, in storage for
years and have had no problems.

Spencer Chase