A little over a year ago I saw a remarkable exhibition of samurai swords at the British Museum. Sharp enough to cut a man in two, yet evidently crafted with a profound and poetic sense of beauty, each one seemed like a paradox made tangible - an emblem of perfect ruthlessness allied to the most finely tuned aesthetic sensibility.
I was impressed in particular by something that Japanese swordsmiths called the hamon, a wavy line resembling mist, or smoke, created where two forms of steel - the hard, cutting edge of the sword and its more flexible back -meet on the blade itself. This visual accident of the process by which such swords were made, a complex folding and tempering of steel, was the secret of the samurai sword's success, enabling it to cut right through a man's skull as if it were a melon. Apparently, Japanese archaeologists can date ancient battlefields according to the condition of the fallen warriors' skulls - if the blade has penetrated down to the jawbone, the sword used to deal the death blow was forged during the heyday of the samurai as a warrior class.

I found it hard to forget those swords, and some months after seeing the British Museum's exhibition - which was at once the brainchild and...