Agate

The number one purpose of any mortar and pestle set is to grind solids into fine powders but under conditions that are highly controlled as to not produce any heating effects and to minimize and control any effects due to stretching of sometimes deformable materials. This is probably the most ancient device one is likely to find in a modern scientific laboratory or kitchen. Because of the ability to control the grinding, and also to virtually eliminate contamination from the mortar and pestle set itself, agate is the preferred material and is used in laboratories and the finest kitchens worldwide to prepare delicate sauces and pastes and for the grinding of dried spices and herbs. From a cross-contamination and cleanliness (hygiene) standpoint if in the kitchen, the high density agate is far more desirable than the more porous porcelain which could grow bacteria in the pores and present a health problem. If a mortar and pestle of metal construction is used, it is generally recognized that metal particles enter the ground powder, thereby presenting either a health concern or else a contaminant is precision scientific measurements are to be made on the ground powder.