HAIR COLORING BY MELANIN PRECURSORS 71 Table II Color Parameter (L) for Cu(II)-Catalyzed Melanization of DHI on Blended Grey Hair at Various pH Values pH L 2.0 15.9 4.O 13.9 9.O 13.2 11.0 13.4 [Cu(II)] = 0.04 M, [DHI] = 0.07 M, color development time 15 minutes values denote merely the intensity of reflectance and these do not necessarily correlate with the quantity of coloring agent deposited within the hair. Nevertheless, the shade intensity imparted by the DHI system is comparable to that obtained from commercial oxidative dye formulations (Table III). It should be pointed out that although in the experiments reported here the color-forming reactions were performed promptly after the metal pretreatment, we have found that the catalyst efficacy is not subject to aging, i.e., the hair can be pretreated with metal salts days or weeks before exposure to DHI to impart the desired color range. PROPERT/ES OF CO•.OREr) Iqam Location of the melanin dye. Microscopic examination of the dyed hair reveals that the melanin is deposited primarily in the periphery of the hair fiber (Figure 4). This is not L 50 30 10 -• x x = bleached hair • o = 9rey hair 1 7 13 [DHI] X 10 -e molar Figure 3. A plot of L values for bleached, blended grey, and brown hair dyed with various concentrations of DHI.

72 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table III Color Parameters (L, a, b) for Grey Hair Dyed With Various Commercial Products and DHI Product L a b Permanent a 14 0.7 2.1 Semi-permanent b 26 0.2 4.2 0.07 M DHI 13 0.1 0.1 0.013 M DHI 12 0.3 --0.2 Clairol Nice N'Easy # 122 Natural Black. Clairol Loving Care #83 Natural Black. surprising in view of the short contact time for both the metal catalyst and the melanin precursor exposure. It is, however, instructive to see that even in this case, the intensity of imparted color is high and matches either the color of natural hair or conventionally dyed fibers (Table III). Color stability. Evaluations, summarized in Table IV, suggest that, in general, the re- sponse of melanin color to a variety of post treatments is intermediate between those of permanent and semipermanent colorants. Bearing in mind the widely recognized chem- ical and physical inertness of melanin, it may appear surprising that the color is not more durable. It is important to make two observations regarding this matter. First, the color deposits, as shown above, are in the fiber periphery and are readily accessible to other reagents, unlike the melanosomes in natural hair which are embedded within the fiber cortex. Second, the melanin deposits, while undoubtedly particulate (TEM Figure 4. Optical micrograph of virgin white hair dyed with DHI. Note ring dyeing only.