does not matter how the resistance of a DLC material is developed, it can be harder than natural diamond in usage. One method of testing the coating hardness is by means of the Persoz pendulum. Bonding of DLC coatings The same internal stress that benefits the hardness of DLC materials makes it difficult to bond such coatings to the substrates to be protected. The internal stresses try to "pop" the DLC coatings off of the underlying samples. This challenging downside of extreme hardness is answered in several ways, depending upon the particular "art" of the production process. The most simple is to exploit the natural chemical bonding that happens in cases in which incident carbon ions supply the material to be impacted into sp3 bonded carbon atoms and the impacting energies that are compressing carbon volumes condensed earlier. In this case the first carbon ions will impact the surface of the item to be coated. If that item is made of a carbide-forming substance such as Ti or Fe in steel a layer of carbide will be formed that is later bonded to the DLC grown on top of it. Other methods of bonding include such strategies as depositing intermediate layers that have atomic spacings that grade from those of the substrate to those characteristic of sp3 bonded carbon. In 2006 there were as many successful recipes for bonding DLC coatings as there were sources of DLC. Tribology DLC coatings are often used to prevent wear due to their excellent tribological properties. DLC is very resistant to abrasive and adhesive wear making it suitable for use in applications that experience extreme contact pressure, both in rolling and sliding contact. DLC is often used to prevent wear on razor blades and metal cutting tools, including lathe inserts and milling cutters. DLC is used in bearings, cams, cam followers, and shafts in the automobile industry. The coatings reduce wear during the 'break-in' period, where drive train components may be starved for lubrication. DLCs may also be used in chameleon coatings that are designed to prevent wear during launch, orbit, and re-entry of land-launched space vehicles. DLC provides lubricity at ambient atmosphere and at vacuum unlike graphite, which requires moisture to be lubricious. Isolated carbon particles embedded diamond-like carbon coatings are the recent development in this area. The wear rate of amorphous DLC can be reduced up to 60% by embedding isolated carbon