Fire Brand and Frost Brand are two very similar artifacts. They are both unaligned long swords that give double damage and +1d5 to-hit against monsters not resistant to fire and cold respectively. Frost Brand is vastly more popular than Fire Brand, because many monsters in Gehennom are fire-resistant. However, note that most of the Astral Plane's monsters are cold-resistant and not fire-resistant. Both can destroy potions carried by their target; Fire Brand can also destroy scrolls and spellbooks.