Volume 9: Phantom of the Ancient Castle, Chapter 5: Rebirth

In contrast, the weapons and armor wielded by the two Dark Knights seemed rather inferior. The dull, lusterless long sword in Vladimir Koff's hands was clearly an antique, yet Komer evidently lacked knowledge in this area.

However, the Dark Knight generously informed Komer that it was one of the creations of the famous Dwarf forge master Ou Yezi from hundreds of years ago, and its rarity could be discerned simply from the choice of materials used to forge this long sword.

The sword, which appeared unadorned to the eye, was entirely forged from a dark series magic metal—Ghostly Sand.

Ghostly Sand was not originally classified as a magic metal, but it possessed certain properties of magic metals and was exceptionally tough. However, to refine the fine grains of Ghostly Sand, melt them into shape, and finally craft them into a Hundred-refined long sword, not only did it require considerable time and effort, but it also demanded expert control of the firing temperature by the Caster.