Arsonist's Oil is a Consumable(Coating). It can be applied to a weapon to give it special properties for ten turns or thrown as a Grenade to inflict its effects in an area.
'It was then that Swires tossed the oil. It splattered the cambion, and all at once its skin of brilliant carmine dulled to dark, a red like cheap wine, and the fiend vented this sound of anguish I almost pitied, for its very affinity to fire was now undone.'
Properties
Single Use
Rarity: Uncommon
Weight: 0.1 kg / 0.2 lb
Price: 25 gp 
UID
ALCH_Soultion_Oil_RemoveResistanceFire
Effect
Bonus action
Coat your active weapon in Arsonist's Oil.
Condition: Coated in Arsonist's Oil
Duration: 10 turns
- Targets with Resistance to
Fire damage become Vulnerable to it instead. - Targets with Immunity are unaffected.
Where to find
Can be crafted via the Alchemy system by combining Sublimate of Frosted Ears and any Ash
Notes
- One of several references to the gnome adventurer Lupperdiddle Swires. Others appear in the descriptions of the Potion of Glorious Vaulting, the Swiresy Shoes and Swires' Sledboard. "Swires" is a reference to the Discworld books.