Coal used for weapon infusion.
It is said that the giant blacksmith of Anor Londo was once the blacksmith of the gods.
Give to the blacksmith in the shrine to allow the use of gems for lightning, simple, and chaos infusion.
Found on the Giant Blacksmith's corpse in Anor Londo. To reach it, take the left route from the Anor Londo bonfire.
Andre's dialogue upon giving him the Giant's Coal:
My, my… The coal of that peaceable giant.
Seems like ages past. I imagine his passing was long ago.
I miss the old bugger, I do.
My thanks. I'll be sure this coal is put to good use.
I'll be smithing weapons never afore seen by the likes of y'!
It's but a small service, to pay my humble respects.