The Greek Gods, by Evslin, Evslin, & Hoopes.
No one celebrated the birth of Hephaestus. His mother, Hera, had awaited him with great eagerness, hoping for a child so beautiful, so gifted, that it would make Zeus forget his heroic swarm of children from lesser consorts. But when the baby was born she was appalled to see that he was shriveled and ugly, with an irritating bleating wail. She did not wait for Zeus to see him, but snatched the infant up and hurled him off Olympus.
For a night and a day he fell, and hit the ground at the edge of the sea with such force that both of his legs were broken. He lay there on the beach mewing piteously, unable to crawl, wracked with pain, but unable to die because he was immortal. Finally, the tide came up. A huge wave curled him under its arm and carried him off to sea. And there he sank like a stone, and was caught by the playful Thetis, a naiad, who thought he was a tadpole.
When Thetis understood it was a baby she had caught, she made a pet of him, and kept him in her grotto. She was amazed at the way the crippled child worked shells and bright pebbles into jewelry. One day she appeared at a great festival of the gods wearing a necklace he had made. Hera noticed the ornament, and praised it, and asked her how she had come by it. Thetis told her of the strange twisted child whom someone had dropped into the ocean, and who lived now in her cave making wonderful jewels. Hera divined that it was her own son, and demanded him back.
Hephaestus returned to Olympus. There Hera presented him with a broken mountain nearby, where he could set up forges and bellows. She gave him the brawny Cyclopes to be his helpers, and promised him Aphrodite as a bride, if he would labor in the mountain and make her fine things. Hephaestus agreed because he loved her, and excused her cruelty to him.
"I know that I am ugly, Mother," he said, "but the fates would have it so. And I will make you gems so beautiful for your tapering arms and white throat and black hair that you will forget my ugliness sometimes, and rejoice that you have taken me back from the sea."
He became the smith-god, the great artificer, lord of mechanics. And the mountain always smoked and rumbled with his toil.