From my brother and my experiences of owning vintage and antique microscopes, the state of the mirrors can vary widely - from pristine to badly corroded. Their state probably reflects their history and how and where stored or used.
The plane mirror of this 1865 microscope is badly corroded and unusable (the concave on the other side good with only minor spotting). Custom made mirrors are expensive and would be hard to replace so tried the typical roll of mirror film sold on eBay. The auction images give the impression it is to glass mirror reflection standards which clearly foil can never be but it is an improvement both for display and use. The film is self-adhesive but opted to just place the disc on the mirror without sticking.
The typical standard roll 200 x 60 cm (with protective film on mirror side) is also being explored as an attractive reflective base for various displayed items.
A molecule built from an E. H. Sargent & Co. vintage molecular model kit (I collect and use vintage kits).
Comments to the author David Walker are welcomed.