33. How Scandinavians Unwittingly Forged Early Steel Swords
The Scandinavian habit of mixing sacrificial bones with the iron that went into their swords did not imbue the swords with any spiritual powers. However, what Scandinavian smiths did not realize was that the bones, like any organic matter, contained carbon, and mixing carbon with iron produces a rudimentary form of steel.
By burning coal alongside their low-quality bog iron, Scandinavian smiths unwittingly produced bone coal – similar to how burning wood produces charcoal. When modern researchers conducted experiments by mixing bone coal with bog iron to forge swords, they discovered that the process significantly improved the sword. Carbon from the bones penetrated up to three millimeters deep into the bog iron, resulting in a significantly stronger weapon.