Changing the Shape of Hair 172 Differences in both the rate and mechanism of the reaction between the two hair types are apparent in Figure 12. The curves indicate that hair from the individual with “non-reactive” or hard to perm hair was undergoing moving boundary kinetics, while easy to perm hair was reacting by pseudo-first order kinetics. This difference could be explained if the diffusion of reagent into unreacted hair was much slower in the non-reactive individual. These data may explain differences in reaction mechanism under similar conditions reported in the literature. Evans et al. reported moving boundary or “contracting area” under some conditions. Reduction of Japanese hair with ATG at pH 9.0 led to moving boundary kinetics, while reduction with cysteamine at pH 9.0 showed a more uniform reduction with no definite reaction front. However, Manuszak et al. reported that SFTK curves fit to pseudo first order kinetics with ATG at pH 9.5.32 Kuzuhara and Hori48,49 followed reduction of Asian hair using microspectrophotometry after methylene blue staining and FT Raman Spectroscopy. Increased staining with methylene blue was equated with increased concentration of reducing agent in the hair after reduction. Treatment with ATG at pH 9.0 resulted in a gradually decreasing staining toward the center of the hair after 3 min and 5 min of treatment, respectively, and complete penetration at 15 min. In contrast this author reported uniform penetration of methylene blue through the hair after 5 min of treatment with sodium thioglycolate at pH 9.0.29 Kuzuhara and Hori pointed out that calculating a diffusion constant (D) is complicated because D is changing as S-S bonds are broken and that that active species is RS-. They were able to calculate apparent diffusion constants. Waving efficacy was measured by the Kirby Method.50 Kuzuhara and Hori’s results at pH 7 and 9, respectively, and 5 and 15 min of treatment, respectively, with ATG are summarized in Table 1.