The mirrored backs of these corner shelves would allow whatever display pieces the owners had to shine nicely in the low light of this period.  The shelves are made of bronze d'oré.  Bronze d'oré, also known as ormolu or gilt bronze, was a decorative finish used on luxury furnishings in the 18th and 19th centuries. An application of finely ground high carat gold and mercury amalgam was placed on objects of bronze. When subjected to extremely high heat, the mercury evaporated, leaving behind a lustrous coating of gold.