The King said, "The sword is good," and he wanted it for himself. Wieland answered, "It is not especially good; it must be made better; I shall not stop till then." The King went away in good humor. Wieland returned to his forge, took up a file, and cut the sword into little pieces which he mixed with flour. Then he released some birds who had been hungry for three days and gave them the mixture to eat. Placing their excrement in the front of the forge, he smelted them and cleansed the iron of all the dross it still contained, and then he forged the sword anew. ^*

Okay, so... I'm not a blacksmith and I only know the basics of the craft, but I'm fairly certain "feeding the sword to birds and making a new one from their shit" is not a common practice. In fact, I'm positive there is no manual out there that suggests this. I'm not entirely certain what bird's digestive fluids and intestinal tract does for a sword, but I'm assuming nothing substantial. I wonder how Wieland thought of this. "Man, what can I do... Bird shit. That's the answer."

Pierre Riché, Daily Life in the World of Charlemagne, translated by Jo Ann McNamara (Philadelphia: University of Pennsylvania Press, 1978), 148.