Sulfurous Ash

Sulfurous Ash is needed for all flammable things or things that have energetic explosiveness like the volcanoes from which it comes.

Source
Sulfurous Ash can be Mined like ore or found near fumaroles which are openings in or near a volcano, through which hot sulfurous gases emerge. It can always be dropped off certain mobs (i.e. Lava Golem). It is found as a white pile of ash deposit or a yellow pile of brimstone.

Trivia

 * Sulfurous Ash is a traditional reagent in Ultima.