Spark testing is an inexpensive, quick and easy way to determine the general classification of a ferrous material or separate materials by general type (carbon steels, alloy steels, tool steels, cast irons, etc.). It can also be used to separate mixed batches of material. Granted, this can be done using portable spectrometers and other alloy-detection devices, but only if they are readily available.
A hand-held or stationary grinder (not a Dremel tool) is usually used to create sparks. The wheel should be large enough to generate a speed of at least 25 m/s (5,000 sfpm), but 38-58 m/s (7,500-11,500 sfpm) is preferred. To calculate this value, multiply the circumference of the wheel (in inches) by the speed of the wheel (in revolutions per minute) and divide by 12.
First, gather and wear all necessary PPE (personal-protective equipment), including a face shield, gloves and eye, face and hand protection. Wear safety shoes, long-sleeved shirts and long pants (a leather apron is helpful and have a bucket of water nearby).
Second, secure the metal in a vice (if using a stationary wheel) and gently contact the surface of the material to the surface of the wheel. Pause between each application of pressure to allow observation of the spark properties. Compare them to known data (Fig. 1).