Diamond coatings are grown in a vacuum chamber using feed gases of hydrogen and methane. Usually the gases are fed into the chamber in a 50-to-1 mix, with hydrogen being the predominant gas. A high-temperature element in the chamber causes the deposition process to take place. For example, sp3 Inc. (www.sp3inc.com) uses fine filaments energized to about 2,200 C to break down the methane into carbon and hydrogen. The carbon atoms then nucleate and grow tiny crystals of diamond and, in time, these tiny crystals grow into a continuous diamond film. Diamond grows slowly, about 0.5 to 1.0 micron per hour. Growing a 40-micron film on inserts can take almost two days whereas most round tools are coated overnight.