The origin of the glow is magical. I like to think that it is some memory of
the light of the Two Trees is involved here, but it is pure speculation.
What bugs me is why there aren't more blades like this. That leads to the
thought that it needed a special smith or special circumstances to make this.
To any knowledge Narsil didn't glow. And Narsil was forged by a dwarf Telchar,
so he wouldn't have had access to the elven knowledge of how to make the swords
shine.
The flame will wake from sleep
The Kings the horn will call
But though they answer from the deep
You may never hold in thrall
Those who ride from Owein's Keep
With a child before them all.G.G. Kay, The Fionavar Tapestry
