Board Thread:Character Discussion Board/@comment-25901581-20151205010407/@comment-26210095-20151205135239

Feanor did it, and Feanor really doesn't give a shit about what the Valar think. He did it as an experiment (in secret) on how to make the Silmarils, although it didn't really work, as the blade was unable to absorb the light from Laurelen. It was Feanor's personal weapon, and when he dies it was given by the sons of Feanor to Thingol as a Thanks you and reconciliation gift. Also, yes it was for cosmetics (in the end, the Silmarils were only 'for cosmetics'), but it did grant certain powers for the blade. Nothing crazy, but it incited fear in your enemies.