The world of Harry Potter comes alive with this "I Solemnly Swear...Mischief Managed" heat changing mug. Fill this mug with hot liquid and the text changes from "I Solemnly Swear That I Am Up To No Good" to "Mischief Managed." This 11-ounce mug changes from black to a creamy, off white color, completing the transformation. This mug makes a great gift for any Harry Potter fan. In our new, improved version of this fan-favorite gift, the disappearing action is much more complete, although you'll still see a hint of the first part of the spell after the hot water is added. Also, while you should still wash the mug with care, the artwork is much more resistant to scratching. Important: This mug is not microwave safe and is not dishwasher safe. Hand wash only with non abrasive cleaner and soft sponge.