JOURNAL OF COSMETIC SCIENCE 434 Table III Weathering Effect on Color Fastness of PPD-MeRES with Direct Sunlight Exposure Colorimetric Parameters Days 0 4 7 11 14 18 24 pH 9.0 L 30.28 29.43 30.93 32.65 33.27 36.01 35.52 a* 9.24 9.07 8.49 7.73 7.51 6.98 6.71 b* 12.7 12.56 12.4 12.41 12.39 12.72 13.07 pH 9.5 L 43.15 42.28 44.2 45.51 47.5 48.05 50.9 a* 8.98 8.77 7.78 7.1 6.61 6.03 5.35 b* 13.36 13.57 13.09 13.06 12.68 13.16 13.31 pH 10.0 L 49.01 48.37 50.91 52.36 54.5 55.39 56.89 a* 8.8 8.62 7.48 6.75 6 5.48 4.97 b* 16.85 16.37 15.39 15.12 14.8 14.95 14.86 pH 10.5 L 48.41 48.16 51.11 52.89 54.76 56.64 58.92 a* 9.1 8.68 7.49 6.66 6.05 5.28 4.62 b* 18.49 17.22 16.08 15.43 15.05 14.91 15.03 Table II Weathering Effect on Color Fastness of PPD-RES with Direct Sunlight Exposure Colorimetric Parameters Days 0 4 7 11 14 18 24 pH 9.0 L 28.61 26.73 27.68 28.91 30.1 31.43 32.41 a* 3.64 3.78 3.98 4.29 4.61 4.46 4.57 b* 11.91 11.08 11.37 11.79 12.16 12.64 13.02 pH 9.5 L 36.78 33.69 35.57 38.18 39.04 40.36 43.5 a* 3.49 3.95 4.18 4.45 4.63 4.43 4.45 b* 15.44 14 14.11 14.43 14.4 14.64 15.43 pH 10.0 L 41.4 40.17 42.34 44.69 46.4 47.82 49.47 a* 2.52 3.46 3.59 3.68 3.81 3.54 3.67 b* 18.04 16.36 15.93 15.47 15.34 15.42 15.74 pH 10.5 L 45.13 45.82 47.68 50.13 52.02 53.39 54.97 a* 2.12 2.94 3.07 3.16 3.16 2.93 2.94 b* 17.56 15.95 15.45 14.98 14.8 14.83 15.02

REACTION OF PPD AND BENZENE DERIVATIVES 435 The colorimetric data of the pigment deriving from the couple 2-amino-4-(2-hydroxy- ethylamino)anisole sulfate (AHA) and PPD (see Table I) show that, in all the range of pH values under study, L, a*, and b* values are typical of the purple-blue color. TLC shows at pH 7.5 the presence of a strong dark brown pigment, with Rf = 0, and a large and strong blue band, with Rf = 0.1–0.25. At pH 9.5 the band with Rf = 0 is light (yellow brown) while the blue band is very strong. Furthermore, the blue band turns slowly to brown by exposure to daylight (Table V). Corbett states that the reaction rate between PPD and aromatic m-diamines is very high. The analysis of the color formed in the tested pH range really suggests that the blue ami- noindamine 3 or the trinuclear derivative 5 are always the main products of the reaction. In spite of this, the pigment formed is very sensible to weathering also in the absence of the direct action of sunlight. The color fades and turns from blue to a purple shade and fi nally to dark brown or dark red (Table V). Table IV Weathering Effect on Color Fastness of PPD-AP at pH 10 without Direct Sunlight Exposure Colorimetric Parameters Days 0 4 7 11 14 18 24 L 27.59 28.56 29.04 29.26 29.4 29.89 30.29 a* 8.31 7.15 6.75 6.36 6.36 5.88 5.93 b* 1 2.54 3.15 3.62 3.75 4.3 4.43 Table V Weathering Effect on Color Fastness of PPD-AHA without Direct Sunlight Exposure Colorimetric Parameters Days 0 4 7 11 14 18 24 pH 9.0 L 18.39 18.72 21 24.25 26.13 28.34 31.05 a* 6.61 4.8 4.05 3.44 3.03 3 2.58 b* −14.38 −10.04 −6.91 −3.77 −2.08 −0.55 −1.32 pH 9.5 L 13.36 13.66 14.36 15.41 16.65 18.11 20.24 a* 4.46 3.97 3.75 3.53 3.38 3.44 3.18 b* −9.13 −8.1 −7.08 −5.84 −4.8 −3.68 −2.25 pH 10.0 L 13.8 14.46 15.59 17.27 18.89 20.83 23.66 a* 3.95 2.78 2.13 1.74 1.56 1.77 1.68 b* −9.98 −7.85 −5.88 −3.71 −2.09 −0.52 1.31 pH 10.5 L 15.86 17.11 19.46 22.25 24.2 27.19 30.92 a* 3.82 2.1 1.23 0.9 0.74 0.86 0.71 b* −12 −8.41 −5.19 −1.87 0.21 2.1 3.9