User blog comment:Maki Kuronami/Lesson 23: Cinder and her flames of eternity/@comment-173.63.194.85-20140912045938/@comment-92.82.173.121-20140912132050

It actualy looks more like carbon, maybe diamond plated which would explain the shine. Would make more sense than metal given Cinder's fire theme. Obsidian looks like black glass, so I think it's unlikely that those blades are made out of obsidian.