User blog comment:Fairy Tail Grand Master/What is the hidden blade made of?/@comment-5221049-20120628225742

I think they use the same technique as they use on the Japanese Katana.

"The forging of could take many days and was highly revered for its inherent art. Many professionals helped make the sword. After one smith would forge the blade, another would fold the metal  and another wold polish the blade. There were even specialists in the creatioin of the sheath, hilt and tsuba (hand guard). The most facinating part of the proces was the folding of the metal. As the name implies, folding is a process in wich the metal is bend over itself and hammered flat, creating multiple layers wich strengthens the blade. The numbers of folds varied from one sword to another, but each foldresults in 2^n layers (were n is the number of folds). A sword folded 12 times would contain 212 some even had over 4000 layers"

If you ask me it's the most logical explenation because if the hidden blade was made of lets say titanium it would be hard for other countries to get it, because not every country or continent has titanium in their ground. But one thing that maybe ruins my theory.

The Katana was developed in the early 15th century, when the feudal era reached its climax during "The Age of States at War".