From Seven 20. This Heat Reveal Coffee Mug features Lumos / Nox Magic spells that activate with heat! The 'magical' mug features a black exterior that reveals an aura of light when a hot beverage is added. Heat reveal works with coffee, tea, hot chocolate, or any warm beverage! A perfect gift for any fan of the Harry Potter book series or movie franchise! Ceramic. Holds 11 ounces.