Sherrill Mudtools MudSponge White Finishing Sponge Tool for Pottery and Clay Artists The Mudsponge White Finishing is pop up sponge made with a tight-cell material. Shaped like the traditional kidney rib to fit comfortably in your hand. made of an environmentally friendly material that is incredibly durable compressed for economy of space and for the fun of watching them expand when introduced to water. 3.75