This is a bespoke Victorian sweetheart overbust corset.  It has a plum dupioni silk cover, lacing panel, and split metal busk.

Core: Two layers of corset coutil
Cover: Plum dupioni silk
Edging: Black double-face satin ribbon
Boning: 4 1/4″ flat spring steel bones, 14 1/4″ spiral steel bones
Piecing: 8 panels per side
Busk: 13″ metal straight double busk