Pumice Powder 25g BAG - 100% natural volcanic rock which has been carefully graded to achieve consistent grain sizes. This pumice powder is graded using 44 microns (325 mesh) as to how fine or course each grade is. This versatile powder maintains a sharp edge, no matter how finely it is ground, and is widely used for hand rubbing of wood prior to final polishing. It is often used by lutheirs in the preparation of musical instruments. 75%+ of grains finer than 44 microns