A lot of potters find them extremely useful.
Cut into a small piece and use it for bisqueware to prepare the vessel for better glazing.
 
Red: softer and provide smoother feel.
Green: very hard (use for larger surface for fast result)
 
Size:
Red: 20x10x1cm
Green:20x13x1.5cm
 
Please note: we highly recommend to wear mask when dusting due to silicosis content in the clay and glazing.