Asymmetrical Mid Century Metalic Grey French 4.5cm Buckle

A polished shiny lucite surface with subtle depths and variations in the colour make this buckle look like its made from molten metal.
And an equally clever design, indented curve on one side, same size curve on the other, but built up (what IS the opposite of indented ?!)
4.5cm tall, and 4.5cm wide.
The inside aperture is just over 3.2cm tall and 7mm wide.