Ancient necklace early ‘900 ‘Concertino’ ‘in 9 kt gold with enamels

Necklace formerly called ‘Concertino’ Mid’800 era in 9 kt gold. It has a large central pendant in perforated foil decorated with an enamelled S in shades of blue, a letter that recurs in many jewels of the time. Very rare and unobtainable popular jewel in excellent condition