A Japanese armour plate (left) and its structure seen under microscope (right)

The metallurgy of Japanese plate armour

The question

Compared to European armour, a very limited amount of Japanese armour has been examined metallurgically. Documentary sources, such as the text of Sakikabara Kōzan published in 1800, suggest that, particularly with the introduction of firearms in the 16th-century, Japanese armourers went to considerable lengths to increase the protection offered by their armour.

Could metallographic examination of some stray plates donated for scientific analysis, tell us more about the metallurgical quality and effectiveness of Japanese armour?

Results of analysis

This section of armour is of composite construction, comprising an outer face of steel (shown as the dark-etching phase in the micrograph above) and an inner lining of pure iron (the bright phase, ferrite). The steel is distinctly harder and tougher which would help prevent the penetration of projectiles, whilst the softer iron behind is ideal for absorbing the energy of the impact.

The content of slag inclusions is exceedingly low compared with other traditionally produced ironwork and the ferrous plate is protected from corrosion by numerous coats of lacquer.


This armour has clearly been constructed from two different carefully chosen and skilfully worked materials, such that even with a thickness of about 1mm the armour would provide the best possible level of protection for the wearer.

A piece of cheaper armour, examined at the same time was constructed entirely of soft iron containing many slag inclusions so the quality of armour may be very variable.


The results of this recent research were first made public in a series of talks that accompanied the Royal Armouries Shogun exhibition in 2005. A broader research project looking at the metallurgy of Japanese armour is now planned.

Did you know?

Stainless Steel

Harry Brearley, chief metallurgist of Thomas Firth & Sons of Sheffield, England, discovers martensitic chromium stainless steel in 1913 while seeking a corrosion-resistant alloy for gun barrels for the British Government.