The Viking sword "Ulfbert" was made of such pure metal that it puzzled archaeologists. It was believed that the technology for making such a metal was invented only 800 years later, during the Industrial Revolution.
The difference lies in the homogeneity of the Ulfberta steel, which contains almost no slag.
Approximately 170 copies of the Ulfbert swords have been found dating back to 800 - 1000 AD. A documentary film produced by Nova and National Geographic called "Secrets of the Viking Sword" was first shown in 2012 and drew attention to the mysterious sword and its composition.
In the process of forging iron, the ore needs to be heated to 3000 degrees Fahrenheit so that it turns into a liquid, allowing the smith to remove impurities (slag. Carbon is also added to the alloy 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 crushing, a less efficient method.
The Ulfbert sword, however, contains almost no slag and has a carbon content three times greater than other metals available at the time. It was made from what is called crucible steel.
Furnaces, invented during the Industrial Revolution, were believed to be the first tools to heat iron to this extent.
The modern blacksmith Richard Farrer from Wisconsin spoke about the difficulties of creating such a sword. Farrer is portrayed in the documentary as one of the few people on the planet with the skills necessary to attempt to make the Ulfbert sword.
"Making It Right Is The Most Difficult Task I Have To Solve," he said, and added that the Ulfbert's Maker apparently had magical powers. “Being able to make weapons out of the ground is pretty powerful." And making a weapon that can bend without breaking, remain sharp and weigh very little is something supernatural.
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Farrer spent many days in painstaking work making such a sword. He used medieval technology. The slightest flaw or mistake can turn the sword into a piece of scrap metal. He announced his success at the end, more with relief than with joy.
It is possible that the material and manufacturing technology of this sword came from the Middle East. The Volga was a trade route connecting the Viking settlements and the Middle East, it opened at the same time when the first Ulfberts appeared, and the last Ulfberts were made when the trade route was closed.