308 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS The color of the cloth patterns was read on a Hunter Tristimulus Colorimeter before and after irradiation. In all, 34 mono-donor nitrobenzenes and 32 di-donor nitroben- zenes were examined. These included nitrophenols, nitroanisoles, nitroanilines, ni- troaminophenols, nitroaminoanisoles, and nitrophenylenediamines and their N-substi- tuted derivatives. In addition, 22 nitrodiphenylamine derivatives were studied. 2O x lo 0 x I I I I -2 0 -12 ++.,.+ + ,.14. .+ * ++ .%, I +8 o Figure 5. The light fastness of nitro-dyes as shown by the values of AL and X (see text). Monosubstituted nitrobenzenes are shown as dots (ortho isomer), open circles (meta), and crosses (para) disubstituted nitro- benzenes are shown as plus signs (0 + m substitution), asterisks (0 + p substitution), and triangles (m + p substitution). Dyes represented by points within small rectangle have good lightfastness.

HAIR COLORANT CHEMISTRY 309 The data obtained consisted of the values of L, a, and b for each test pattern before and after irradiation. These parameters are: L, lightness or reflectance a, redness when positive, and greenness when negative b, yellowness when positive, and blueness when negative. If we define AL as the change in lightness and X = ,/{(A a) 2 + (A b) 2} as the change in color tone resulting from irradiation, it will be evident that small values of AL and X indicate stability to light. In Figure 5, values of AL and X for all the dyes studies have been plotted. It can be seen that, in general, large changes in AL are accompanied by large changes in X. Also, •~• b --20 NO:• Figure 6. Tonal stability of some nitroanilines and nitrophenylenediamines plotted on an a, b color plane. Tails of arrows indicate color before, and heads color after, irradiation. The longer the arrow, the less lightfast the dye. I I I I -lO o lO 30