The famed Ulfberht Viking swords were made of metal so pure it baffled archaeologists. It was thought the technology to forge such metal was not invented for another 800 or more years, during the Industrial Revolution.
About 170 Ulfberhts have been found, dating from A.D. 800 to 1,000. A Nova National Geographic documentary titled “Secrets of the Viking Sword,” first aired in 2012, took a look at the enigmatic sword’s metallurgic composition.
In the process of forging iron, the ore must be heated to 1,650 degrees Celsius (3,000 degrees Fahrenheit) to liquify, allowing the blacksmith to remove the impurities (called “slag”). Carbon is also mixed in to make the brittle iron stronger. Medieval technology did not allow iron to be heated to such a high temperature, thus the slag was removed by pounding it out, a far less effective method….