Adhesive wear was defined in Chapter 2 as “progressive loss of material from or damage to a solid surface in rubbing contact caused by solid-state bonding (adhesion) between the rubbing surfaces.” Examples of adhesive wear that everyone is familiar with, but may not recognize, are chalk on a blackboard and writing with a pencil on paper. In the former, chalk is transferred to the smooth and harder-than-chalk blackboard. The blackboard can be made from slate or any rigid material with a nonshiny, unlubricated surface. In the latter, soft graphite (lead) is transferred to smooth but porous paper. If a pencil mark is observed under a microscope (Figure 3.1), it will appear black, as platelets deposited on the peaks of the interlocked fibers that constitute a paper surface.