a rougher surface which helps to reduce the particle size. Glass mortars and pestles are fragile, but stain-resistant and suitable for use with liquids. However, they do not grind as finely as the ceramic type. Other materials used include stone, often marble or agate, wood (highly absorbent), bamboo, iron, steel, brass, and basalt. Mortar and pestle sets made from the wood of old grape vines have proved reliable for grinding salt and pepper at the dinner table. Uncooked rice is sometimes ground in mortars to clean them. This process must be repeated until the rice comes out completely white. Some stones, such as molcajete, need to be seasoned first before use. Metal mortars are kept lightly oiled. Automatic mortar grinder Since the results obtained with hand grinding are not easily reproducible, most laboratories use automatic mortar grinders. Grinding time and pressure of the mortar can be adjusted and fixed, saving time and labor. The first automatic Mortar Grinder was invented by F. Kurt Retsch in 1923 and named the "Retschmill" after him. Advantages The use of mortar and pestle, pestling, offers the advantage that the substance is crushed with low energy so that the substance will not warm up. Gallery See also Cupstone Dheki Makitra Metate Millstone Muddler Molcajete Oralu kallu Quern-stone Stone and muller Suribachi and surikogi Usu and Kine, large pestle and mortar used in the production of Mochi Yagen Household Stone tools in Karnataka The Knight of the Burning Pestle References External links Example of an automatic mortar grinder Food grinding tools Alchemical tools Laboratory porcelainware Laboratory equipment Professional symbols Kebaran culture