at the desired level. A talented smith or metalworker can fine-tune the performance of a steel tool or item to precisely what is required based solely on careful observation of temper colours. A visual representation of this process may make the concept easier to understand. Testing for hardened steel It is not easy to determine if steel has undergone the hardening and tempering process by simply looking at it, but there is a reliable and simple test. To examine a piece of steel, obtain a hand file and file an edge of the selected metal. If the piece of steel has not undergone the hardening process, the metal file should easily 'bite' into the sample. If the metal has been hardened, the file fails to cut into the sample and glances off with little visible effect. Case hardened articles starting as low carbon steel (0.5 - 1.5% carbon content) can also be labeled hardened steel. References Steels