National Geographic : 1942 Apr
J.H.Schaefer and Son With Faces Masked Against Flying Sparks, They Grind Billets of Stainless Steel In this Baltimore plant every bar is ground with an abrasive wheel to remove scale and surface imperfections. Metals alloyed with steel figuratively write their names in the spray of sparks from a high-speed wheel. An expert can quickly tell the dull-red spark of high-tungsten steel from theorange spear points of molybdenum steel or the tiny blocks of brilliant white light characteristic of nickel steel. Spark testing is oftenused forseparating steels that have been mixed.