Alkahest

Alkahest, otherwise known as the universal solvent is the second hardest material for any alchemist to make. When being described it was mentioned that it could dissolve anything, and the substances given as examples were wood, steel, and flesh. In order to contain it, alkahest is stored in a bubble of itself, in which it hovers above a ring of fire on the floor. It was mentioned that it appeared to be a milky liquid that danced with the flames.