158 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS to actively support a cooperative research project that led to the results that are presented in this paper. REFERENCES (1) (2) (3) (4) (5) (6) (7) (8) (9) (lO) (11) (12) (13) (14) (15) (16) (17) (18) M. Feughelman, The physical properties of alpha-keratin fibers, J. Soc. Cosmet. Chem., 33, 385-406 (1982). C. R. Robbins, Chemical and Physical Behaviour of Human Hair, 2nd ed. (Springer Verlag, New York, 1988). F.-J. Wortmann and I. Souren, Extensional properties of human hair and permanent waving, J. Soc. Cosmet. Chem., 38, 125-140 (1987). C. R. Robbins and R. J. Crawford, Cuticle damage and the tensile properties of human hair, J. Soc. Cosmet. Chem., 42, 594 7 (1991). L.J. Wolfram and M. K. O. Lindemann, Some observations on the human hair cuticle, J. Soc. Cosmet. Chem., 22, 839-850 (1971). J. A. Swift, "The Hair Surface," in Hair Research-Status and Future Aspects, C. E. Orfanos, W. Montagna, and G. Stfittgen, Eds. (Springer Verlag, Heidelberg, 1981), pp. 65-72. F.-J. Wortmann and N. Kure, Bending relaxation properties and permanent waving performance, J. Soc. Cosmet. Chem., 41, 129-139 (1990). N.H. Chamberlain, The sulphur content and regain of descaled human hair, J. Text. Inst., 23, T13-T16 (1932). J. W. Snaith, A method for removing the outer layer of animal fibers, Text. Res. J., 30, 543 (1960). G. V. Scott and C. R. Robbins, Stiffness of human hair fibers, J. Soc. Cosmet. Chem., 29, 469-485 (1978). E. F. Denby, A note on the interconversion of creep, relaxation and recovery, Rheol. Acta, 14, 591-593 (1975). M. Feughelman and M. S. Robinson, Some mechanical properties of wool fibers in the "Hookean" region from zero to 100% relative humidity, Text. Res. J., 41, 469-474 (1971). F.-J. Wortmann and S. DeJong, Nonlinear viscoelastic behaviour of wool fibers in a single step stress relaxation test, J. Appl. ?olym. Sci. 30, 2195-2206 (1985). H. D. Weigmann, L. Rebenfeld, and C. Dansizer, Kinetics and temperature dependence of the chemical stress relaxation of wool fibers, Text. Res. J., 36, 535-542 (1966). M. Feughelman, A. R. Haly, and J. W. Snaith, Permanent set and keratin structure, Text. Res. J., 32, 913-917 (1962). E. T. Kubu and D. J. Montgomery, II: The kinetics of the reduction of wool keratin by cystine, Text. Res. J., 22, 778-782 (1952). H.-D. Weigmann, L. Rebenfeld, and C. Dansizer, A transition temperature in wool fibers under stress in relation to temperature, Text. Res. J., 35, 604-611 (1965). S. D. Gershon, M. A. Goldberg, and M. M. Rieger, "Permanent Waving," in Cosmetic Science and Technology, Vol. II, M. S. Balsam and E. Sagarin, Eds. (Wiley Interscience, New York, 1972), pp. 167-250.

j. Soc. Cosmet. Chem., 45, 159-165 (May/June 1994) A quantitative study of dyeing with lawsone B. I. H. AMRO,* K. C. JAMES, and T. D. TURNER, Welsh School of Pharmacy, University of Wales College of Cardiff, P.O. Box 13, Cardiff CF1 3XF, United Kingdom. *Department of Pharmacy, University of Jordon, Amman, Jordan Received May 24, 1993. Synopsis Bleached wool felts have been dyed with lawsone, and reflectance spectra recorded in the visible region. These spectra were converted to L.a.b. values by computer. A dissolution technique that could be operated at prearranged pH values was developed, and L.a.b. values of dyed felts were recorded before and after extraction. A theory linking dyeing performance to electrolytic dissociation of lawsone and keratin pro- tonation was developed from the results. INTRODUCTION Hands-on experience over many years has established that when the hair is dyed with henna, the pH of the medium must be acid. This appears to be in conflict with the solubility behavior of lawsone, the principal coloring agent of henna. Lawsone is a weak acid and forms soluble salts in alkaline solution, but the undissociated form has a limited solubility in water, so that in acidic suspensions of henna, in concentrations used in hair dyes, not all the lawsone is dissolved. The lawsone in solution will be the active species, with the suspended excess providing a reservoir to replace dissolved lawsone lost to the hair. The more lawsone there is in solution, the greater the driving force of the dyeing reaction. The second conflict between practice and theory is that acid solutions of lawsone are colorless, but as the pH values are increased, an absorption maximum develops around 450 nm (1), giving the characteristic color of hair dyed with henna. Practical experience suggests the opposite behavior and has been confirmed with wool felts (1), which developed deep colors when dyed at around pH 4, but whose colors diminished pro- gressively with increasing pH, until at pH 7 the felts were virtually colorless. We attempt below to rationalize these differences. 159