In the Middle Ages and throughout the sixteenth and seventeenth centuries, armour was made from iron or an alloy of iron. Although steel is stronger than iron, armourers at the royal workshops at Greenwich – where this helmet was made – continuously experimented with methods to make it even tougher. These sophisticated processes involved heating the steel to a cherry red colour at around 800ºC and quenching it in oil or water, and then heating it again at a lower temperature in order to 'temper' the metal and make it less brittle. The resulting steel might be up to four or five times harder than iron. Recent investigation into the metallurgy of this helmet demonstrates that the skull has been both quenched and tempered to make it harder and tougher.