From The Shrunken Monkey website:

"The Screaming Volcano. Limited Edition, the latest release by The Shrunken Monkey, made of Stoneware in two glaze variants. A beautiful molten gloss fluid stone look and dormant rough lava rock stone texture. each mug is 6.75” tall, 4” wide comfortably holds 14 fluid ounces. These mugs are handmade and glazed individually so no two will be exactly alike. Stoneware, dishwasher safe, but recommended hand wash only."