The author takes poetic license with the story.  In the original story, as told in Snorri's Edda, the sons of Ivaldi (a group of dark-elves or dwarves) make golden hair for Thor's wife Sif, the unerring spear Gungnir for Odin, and the ship Skidbladnir for Freyr. Here the dwarves' wives assist in the creation of Sif's hair:

"To Ivald's sons, then, in the farthest and brightest corner of the hall, Loki went. They very readily agreed to make the golden hair for Sif, and they began to work at once. A lump of purest gold was brought and thrown into the glowing furnace; and it was melted and drawn, and melted and drawn, seven times. Then it was given to a merry brown elf, who carried it with all speed to another part of the hall, where the dwarfs' pretty wives were spinning.

"One of the little women took the yellow lump from the elf's hands and placed it, like flax, upon the distaff of her spinning wheel. Then she sat down is and began to spin; and while she span, the dwarf wives sang a strange, sweet song of the old, old days when the dwarf folk ruled the world. And tiny brown elves danced gleefully around the spinner, and the thousand little anvils rang out a merry chorus to the music of the singers. And the yellow gold was twisted into threads, and the threads ran into hair softer than silk and finer than gossamer. And at last the dwarf woman held in her hand long golden tresses ten times more beautiful than the amber locks Loki had cut from Sif's pretty head."