What are the requirements to craft Demon weapons? Or weapons that require a specific Demon's soul to make?
Like I'm trying to craft the curved sword with Soul of Quelaag, and I've tried using both a +10 Scimitar and a +10 Laito/Iaito, and neither seem to work. Do I need a specific Ember? A specific Blacksmith? I've tried bot the blacksmith outside Sen's Fortress and the one in the ruins under Firelink (with the ghosts).
I'm not sure what the sword is called, it's gone by a few names, like Quelaag's Fury Sword, Chaos Sword, etc, but every source I've seen says it requires a +10 Curved Sword and Soul of Quelaag. Whether it means Katana or just a generic Curved Sword, I've got a +10 of both. So what am I missing?