The slider tilted to its left side-edge and formed a wedge sideway. Its interference fringe pattern is shown in Fig. 6. A shift occurred in the fringes as they passed from Regions I to II. Relative to those in Region I, the amount of displacements of the set of fringes in Region II was equivalent to the optical path difference between the two regions at approximately λ/4 (wavelength of the light, 635 nm). The lower plane in Region II is the result of material removal. Furthermore, while the lower plane is darker in shade which is probably attributed to the increase in roughness, a distinct and brighter narrow strip was formed at the inlet edge as shown in Fig. 6. Similar tests were repeated by different operators and the phenomena as shown in Fig. 4, Fig. 5 and Fig. 6 were confirmed. The measured profile of the typical tested surface as shown in Fig. 4 provides clear evidence of material removal and roughened surface at the inlet (Region II). Moreover, chemical analyses of the BSA solution after tests showed the existence of a very small amount of Fe ions. Recently, Fan et al. [17] and Myant et al. [21] performed experiments with a CoCrMo ball on a glass disc contact lubricated by BS, albumin and γ-globulin solutions, and they observed that wear occurred on the ball surface shortly after the start of the test, but the glass disc surface was mostly undamaged. They attributed the damage on the ball surface to third-body wear or chemical polishing (corrosion). In the present experiments, the slider-disc contact was always run under full film hydrodynamic lubrication such that no mechanical wear incurred. The observed material removal at the inlet region could only be attributed to chemical corrosion, which occurred right after the test was started.