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You can experiment even without removing the old coating.
An alternative to silvering the back surface, is to make it black. So that it 
does not participate in forming the image at all.
Removing silvering and making it black
is much easier than silver/aluminium coating.

Just try, and see what happens with your glasses in their present state.
What you will see depends on the state of the remaining silvering.

You may see two reflections, but I expect it will be easy to tell
which is which. They will be of different brightness.

Alex. 

P.S. I can find an old recipe for "silvering" sextant mirrors with mercury,
if you are interested. (Mercury is considered nowadays a dangerous substance to work with).
A supply of mercury was usually available for use in an artificial horizon in old times.

When I was a boy, I silvered things with real silver, using the spent solutions from 
photo film/prints development. (In those times we all developed our films 
ourselves, using a chemical process,
and I byproduct of this process was a solution which contained enough silver.)

A.

   

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