Figure 4. (A) L*, (B) a*, and (C) b* for three shades on copper-treated hair as a function of copper levels. REDOX METALS IN COLOR FORMATION IN A HAIR COLORANT 275

Figure 5. Dye formed in the HDAP–AHT couple. Figure 6. Correlation of UV absorbance of dye extracted versus copper level in hair. and this formed color is subsequently washed out during rinsing off the colorant. This leads to a lighter fi nal hair color. CHELANT EXPERIMENTS Experiments were performed to demons trate that chelants added to a shampoo can re- move copper from hair and improve color uptake and color intensity over multiple washes. The chelant chosen was L-histidine, an amino acid known to have high binding JOURNAL OF COSMETIC SCIENCE 276

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