The fluff I wrote for my Chaos mage has reagents being items that had an emotional connection attached to them by a previous owner. Chaos is an eclectic tradition that "borrows" from where it sees fit. It's cast by feeling out the mana, not by logical formula. So I imagined that chaos mana would pool within things that had been the object of strong feeling. Child's favorite toy, old piece of jewelry, little knick knacks, murder weapon, favorite book, old carpenters hammer, etc.