342 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS JINDN8 I STYLUS DEFLECTION ß SCAN LENGTH _ 130 •m 800 um Figure 1. Typical surface profile. The amplitude of the stylus deflection is plotted versus scan length. called the surface profile and represents the peak and valley geometry of a line on the skin's surface (Fig. 1). The following criticisms have been made of the stylus method: 1) distorted profiles may result from the phenomenon called ploughing, this occurs when the stylus tip ploughs through the ridges 2) attenuation of the signal due to the dimensions of the stylus tip (range from 5 to 20 #m) may be significant 3) elastic deformations of the surface may yield a distorted profile and 4) a two-dimensional profile does not always adequately characterize a surface's texture. IV. PROFILE CHARACTERIZATION Several methods of quantifying the surface profiles' characteristics have been devel- oped. Some of the quantities used have been borrowed from the metals industry and others have been developed specifically for quantifying the skin's topography. ••q Sm S 30 •m 800 um Figure 2. Geometric interpretation of depth of roughness, Rr, scan length, I, maximum peak height, R•, profile curve length, $, mean peak spacing, Sm and mean slope of the profile, Aq.

PROFILOMETRY OF SKIN 343 30 um 800 um Ra= '• ly(x)ldx Figure 3. Geometric interpretation of mean surface roughness or mean roughness value, Figures 2 through 6 contain schematics of the same surface profile obtained from a replica of the lower leg, lateral aspect. On each of these profiles is shown the geometric interpretation of the various quantities which have been used to characterize the surface profiles. What follows is an explanation of each quantity. Referring to Figure 2, 30 •,m 800 •,m x DATUM ...... ...... Rp = T y(x)dx Figure 4. Geometric interpretation of depth of smoothness. R•.