Toso is the clay made by mixing sawdust of paulownia with shofu-nori (wheat starch paste) and is sometimes blended with washi (Japanese paper) in order to provide strength.
桐の粉末に正麩糊（しょうふのり）をまぜて作った粘土で、強度を出すために和紙が混ぜ込まれているものもある。