Sherrill Mudtools MudSponge Blue Workhorse Cleanup Tool for Pottery and Clay Artists A great all-purpose pop-up sponge made of an open cell material that is very absorbent. 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