Sword on the left: A 2-handed iron jian originating from the State of Chu and dating from the late Warring States Period. It is 1.2 meters long. The development of these original 2-handed iron / steel swords occurred during mid-to-late Warring States Period (350 -300 BC); during this time, the slow and steady adoption of steel (replacing bronze) for the manufacture of swords stimulated the lengthening of the blade and handle grip -- as longer steel swords were easier to manufacture, compared to casting long bronze swords, which was more difficult to execute. The States of Chu, Yan, Zhao and Han were especially famous for their production of steel weapons during this time, prompting even the King of the State of Qin (an ancestor and a few generations ahead of the First Emperor of China) to comment that he had " heard of the sharpness of the iron swords from the State of Chu..."
Sword on the right: A steel jian from the State of Yan and also dated to the late Warring States Period (around 300 BC or slightly later). Overall length: 100.1 centimeters, blade length: 80.2 centimeters, handle length: 19.9 centimeters. This weapon was excavated from a graveyard of buried common soldiers with their weapons. Scientific analysis of fragments of other steel swords excavated from the same grave indicate that such weapons were forged / folded and quench-hardened; cross-sectional analysis reveals higher and lower carbon steel layers of 0.5% - 0.6% carbon and 0.15% - 0.2% carbon respectively.
