spiegel : Idioms & Phrases

• noun pig iron containing manganese; used as a deoxidizing agent and to raise the manganese content in making steel
  spiegeleisen; spiegel.
  

WordNet

Spie"gel i`ron

Etymology

G. spiegel mirror + E. iron.

Definitions

1. (Metal.) A fusible white cast iron containing a large amount of carbon (from three and a half to six per cent) and some manganese. When the manganese reaches twenty-five per cent and upwards it has a granular structure, and constitutes the alloy ferro manganese, largely used in the manufacture of Bessemer steel. Called also specular pig iron, spiegel, and spiegeleisen.

Webster 1913