How to get Smithing Stones in Elden Ring Nightreign and upgrade weapons

Puzzling out how to upgrade weapons in Elden Ring Nightreign is a little confusing, especially as its Smithing Stones work a little differently to how they did in the original game. You'll still have to track down this blacksmithing material, but you'll only need one of each kind to upgrade a weapon. Each armament also has a rarity now, which changes what stone you need to use.

Besides the materials, you'll also need to find an anvil out in Limveld, and all the while you're doing this, night...