Curious Little 18th Century Baroque Bronze Mirror, Oxidized Mercury Glass

Very curious little baroque mirror to hang, 18th century, Louis XV-Transition period.
Beveled oval glass surrounded by a lively bronze frame.
The tin, with mercury, seems to have undergone a circular and concentric chemical reaction (which I cannot explain), which gives it a mineral appearance, close to an agate, with mauve and silver reflections.
Near the center, sinuous lines and very shiny points attest to the presence of tin, undercoat before mercury of "Venetian" mirrors since the 15th century. The back of the mirror, just as interesting as the front, has a bronze plate animated by undulations in high relief, and set around the edge with extreme care by a multitude of tiny punched staples.
A frieze decorated with fine floral motifs in relief, vertically encloses the oval where the glass rests by about 1 cm.
It should also be noted, anecdotally, that, on the face, the baroque bronze frame with scrolls, flowers and asymmetrical clasps is pinker and contains more copper than the lower third with ribbon knot and laurels, more yellow, and of a different, more classical style...
Could this be a later Louis XVI addition? Or has this mirror, originally face-to-hand, been the subject of a subsequent transformation, that caused the alteration of the tin??...
I don't have the answer, these are only suppositions after observations... The only certainty I have is that the secret life of old objects never ceases to fascinate us..., a true joy!
Very good general condition.
Height = 19 cm; Width = 10.2 cm; Thickness between 12 and 19 mm; Weight = 248 grams
Very careful shipping in addition, price according to distance...