The shaping processes for traditional ceramics require that the starting material be in the form of a plastic paste. This paste is made of fine ceramic powders mixed with water, and its consistency determines the ease of forming the material and the quality of the final product. The raw ceramic material usually occurs in nature as rocky lumps, and reduction to powder is the purpose of the preparation step in ceramics processing. Techniques for reducing particle size in ceramics processing deliver mechanical energy in various forms, such as impact, compression, and attrition. The term comminution is used for these techniques, which are most effective on brittle materials, including cement, metallic ores, and brittle metals. Two general types of comminution operations are distinguished: crushing and grinding.