5" x 3.5"
No glaze but that which came from the inside of Earth, exploded pumice that broke through the ocean's surface, flew about and then settled back onto the seafloor where it continued morphing until humans picked it up, tightened the bucket lid and delivered it to me. Now it's melted pumice/mud on a chattered clay surface--evidence of silica-rich magma.
NOTE: slightly out of round when looking down from the top. Glass thumbwell.