I've been fascinated by pattern-welded (or Damascus) steel for a long time now. Modern pattern-welded steel refers to a technique where two dissimilar metals are forged together and then etched to bring out the difference between the steels. You can see my modest attempts at this technique on my "metalworking" page. Professional examples can be found here, here, here, here and here. Damascus steel swords can be seen here, here, here or here. A similar, but more challenging technique forge welds precious metals together: Mokume. Artefacts made from Damascus steel date back to before 500 AD. There is a second type of Damascus steel, so-called Wootz. It is not made by forge-welding, but instead the two dissimilar metals are liquified and then solidified in a closed crucible. The exact technique probably originated in India got lost some time in the 18^th or 19^th century. To this day, nobody can reproduce this exact type of steel.
The more interesting is an article in the journal Nature on an historic blade from the 17^th century. This article details how the authors used transmission electron microscopy to detect carbon nanotubes and cementite nanowires in the ancient steel. They attribute some of the superior properties of the steel to these nano-structures. I have appended the full text of the article in the extended news post, as you need a subscription for it. However, neither the references nor the figures are reproduced. The figures can be found (along with an excellent article in German) in a related SPIEGEL article. NewScientist and the Telegraph both have articles on these findings.

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