KINETICS OF HAIR REDUCTION 289 of EDTA disodium salt (0.55 g), sodium laurel sulfate (12.5 g), and 100 mg of the ABD-F fluorochrome. All work was performed at room temperature in a nitrogen atmosphere. Small-fiber bundles were dampened, immersed in approximately 20 ml of the appropriate reducing solution for 20 minutes, rinsed, and soaked in the ABD-F solution overnight (approx. 15-18 hr). Upon removal from the ABD-F solution, the fibers were rinsed and left to dry in loosely covered petri dishes before being removed from the nitrogen environment. These studies were performed using a Zeiss Axioplan microscope, equipped with a 35-mm camera and fluorescence attachments. The source was an Osram HBO 50 mercury short-arc lamp, and an Omega filter set was used that included exciter filter 360WB50, chromatic splitter 400 DCLP, and barrier filter 430EFLP. RESULTS AND DISCUSSION Figure 7 shows an experimental reduced-time plot for a series of SFTK experiments involving the reduction of Japanese hair with 0.42 M ammonium thioglycolate (ATG) at pH 9, temperature = 25øC. It is observed that upon normalization the experimental data falls onto a common curve, indicating the applicability of a single kinetic behavior. It may be argued that as this data was generated from a single hair type, using a given reducing agent, a single kinetic behavior should be expected. However, due to the fiber-to-fiber differences, even using hair from a single head, this conclusion may not be readily observable without normalizing the time axis. This behavior has been compared to the theoretical curve for Mampel's contracting area model (Eq. 15), and it is observed that a reasonable correlation is seen up to ot=70%. Based on the applicability of this model, we may predict that the reduction occurs by a diffusion-controlled process via the 0.9 ' ' •.//'• •' ' 0.8 0.7 0.6 0.5 0.4 0.3 0.2 •,,•, I 0.0 , .... • .... I .... • .... • .... • .... • .... 0.0 0.5 1.0 1.5 2.0 2.5 3.0 .3.5 4.0 t/to.5 Figure 7. Reduced-time plot for a series of SFTK experiments using Japanese hair in conjunction with ATG at pH 9, 0.42 M, 25øC. Data are compared to the theoretical curve for the contracting area model.

290 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Figure 8. Fluorescence microscopy image taken during reduction of Japanese hair with ATG solution (pH 9, 0.42 M), demonstrating the presence of a distinct reaction interface. movement of a well-defined reaction interface. Figure 8 shows a fluorescence microscopy image taken during this reaction, demonstrating the presence of such an interface. Figure 9 shows another experimental reduced-time plot, this time showing data from the reduction of Japanese hair with 0.42 M cysteamine at pH 9, temperature = 25øC. This data is also compared to the theoretical model for the contracting cylinder expres- sion, which is shown solely for reference purposes. Although there is more variability in the data, it can be seen that this plot does not give rise to the same shaped curve as was seen previously. In the early stages, it is observed that the points lie above the con- tracting cylinder theoretical plot, whereas these points drop below the theoretical above ot•0.6, and have only reached a•0.8 by t/to. 5 = 4.0. Therefore, it can be concluded that cysteamine is reacting via a different kinetic pathway to that seen with ATG. Figure 10