In the first four ages humans didn't use physical fire for they could use spiritual fire. But in the Fifth Age, when the Draught of Forgetfulness was taken by the Aryani, the Physical Fire mysteries, which formed one part of the Vulcan secrets, was taught to the Blacksmiths who were from the lineage of Cain.
To them was given the sanction to use the black or earthly aspect of fire which was seen as a 'black mystery'. They had to strike with a hammer or to smite - Hence they were called Blacksmiths.
Lesser Blacksmiths made tools and utensils fashioned from metals, by employing air and fire and water to transform them.
The highest of all Blacksmiths created the Sword of Anwn or the 'Sword of the World' with Aryanian Steel. It was woven with spells and on its pommel lived the Oculus, the Magical Sun Stone.
The Oculus fell out of the sword's pommel before the Sun Manu slipped into the Sea of Glass in the Fifth Age when he brought down the Dark Faced Lord and his Brothers of the Shadows.