Coal used for weapon infusion.
Long ago, used to forge the greatswords of the Undead Legion of Farron.
Give to the blacksmith in the shrine to allow the use of gems for heavy, sharp and poison infusion.
Found on the Road of Sacrifices. From the Halfway Fortress bonfire, go downwards and drop down the ledges on the right side. Keep going straight forward along the right wall and enter the doorway at the end. Turn to the left to see a Black Knight next to a corpse. Ths Farron Coal is on the corpse.
Andre's dialogue upon giving him the Farron Coal:
Oh, my… this coal is from the Undead Legion…
Used to forge the weapons of Farron's Abyss Watchers.
A fine prize. I'm honoured to be endued with it.
Now I'll be equipped to infuse special gems.
Praise the gods, eh. Time to put this brawn to use!