Arcane Dust is a Magic crafting material in Diablo III, obtained by using the Blacksmith to salvage magic weapons and armor. Blue items of any level will yield 1-4 Arcane Dust.
Sometimes monsters and objects can drop Arcane Dust as well.
It can be stacked up to a maximum of 5000. Arcane Dust is account bound. It is used in crafting rare, legendary, and set items, as well as enchanting and transmutations.