Aqua regia

In the 8th century AD, an alchemist by the name of Jabir ibn Al-Hayyan prepared the first recorded batch of aqua regia, a mixture of nitric and hydrochloric acid in a 1:3 ratio.

Named from the Latin for ‘royal water’, this volatile mixture turns from colourless to a fiery yellow–orange within a few seconds of preparation. For further dramatic effect, it fumes vigorously. Because its components are so volatile, it is usually only mixed immediately prior to use. If left for a period of time, the concentrated nitric and hydrochloric acid react together to form products such as nitrosyl chloride and chlorine – neither of which you want hanging about.