Bentonite 325 Mesh MBEN325 1 KgBentonite 325 Mesh MBEN325 Al2O3. 4SiO2. H2O A very fine grained plastic clay of volcanic origin containing colloidal matter. Used in small amounts as an additive to clays to aid in plasticity and in glazes as a suspending and binding agent. Bentonite 325 A sodium bentonite. The most commonly used bentonite, and is considered a standard glaze and clay additive. It can at times be coarser than 325 mesh, and may cause some specking if used in amounts