An elementary but fairly accurate test for the identification of steel by observation of the spark pattern produced during grinding.
When a steel bar is held against an emery wheel, the end of the bar is heated by friction. As the small particles, or sparks, are thrown from the wheel, they will follow a straight line which becomes broader and more luminous some distance from the source of heat before disappearing. This is probably due to the exposure of the heated particles to the oxygen in the air, which requires some time to react. Note: Touch the material lightly to the wheel; observe individual spark. Use black background.
