Metallic iron with sufficiently high phosphorus content to appreciably harden the metal. Phosphorus will increase the rate of work hardening, making the metal more brittle. Thus high phosphorus iron is more difficult to work than a low carbon bloomery iron, especially at low temperature. However, high phosphorus irons have been used selected for specific uses in a number of periods – during the Iron Age it seems to have been used for larger edge tools as a alternative to carbon steel. During the Anglo-Saxon period when many of the pattern-welded sections of composed of alternating bands of high and low phosphorus iron. In the 18th century, high phosphorus iron wires were used for harpiscord and early piano wires.