These include grinding, milling, and mechanical alloying techniques. Provided that one can produce a coarse powder as a feedstock, these processes utilize the age-old technique of physically pounding coarse powders into finer and finer ones, similar to flour mills. Today, the most common processes are either planetary or rotating ball mills. The advantages of these techniques are that they are simple, require low-cost equipment and, provided that a coarse feedstock powder can be made, the powder can be processed. However, there can be difficulties such as agglomeration of the powders, broad particle size distributions, contamination from the process equipment itself, and often difficulty in getting to the very fine particle sizes with viable yields. It is commonly used for inorganic and metals, but not organic materials.