Potassium Nitrate

Potassium Nitrate is a low-profile fuel enhancer that keeps fires discreet while making them burn meaner. Try buying a kilo of potassium online, and the feds will think you've gone bananas. Buy a kilo of its nitrate variant, and they'll assume you're halfway through writing your own manifesto. Also known as saltpeter, this crystalline salt acts as the oxidizing agent in gunpowder. On its own it won't do much, but mix it with fuel and you’ll get something dangerously volatile that scorches one spot hotter than the inside of a McDonald’s apple pie.