Since prehistory man has been aware of the importance of particle size in producing resources and wares with desired properties. Archeological evidence indicates that paints used for cave wall paintings are mixtures of finely pulverized pigmenting materials, predominantly carbon, ochre and hematite. Man came to realize that adding pulverized materials to clay not only improved its workability, but improved the drying process, reduced shrinkage and changed the characteristics of the resulting vessels. There also is evidence of using particles of certain sizes to control porosity. For many centuries, finely divided, calcined lime powder or gypsum mixed with sand was used in plasters and binders. Then, about 2000 years ago, the Romans improved upon the formula by adding volcanic (pozzolanic) ash, which produced a superior hydraulic cement that was used in building many structures that still stand. Today, finely divided particulate materials and objects that incorporate or are produced from these fine particles are everywhere about us. Frequently encountered powders include cement, lime, fertilizer, cosmetic powders, table salt and sugar, detergents, bath and dental powders, coffee ...