PERMANENT WAVING OF HUMAN HAIR: THE COLD PROCESS 111 Figure 4.--Hair fibers showing trichor- rhesis nodosa. Hair such as this will tend to show breakage during a waving process. 55 X magnification. Basic filchsin stain v•gurc 5.--wamageu fiber showing longi- tudinal splitting. 50 X magnification. Basic fi•ch•in stain classes-hot and cold--both at- raining the same end but differing in approach. In the hot method the hair is treated with an alkaline sulfite solution and wrapped around a rod of small diameter. lieat is then applied to transform perma- nently the hair from a straight to a curled state. Originally the heat was supplied bv means of electrical heaters, but in recent years chemical heating compositions giving off' an accurately gauged amount of heat have, to a considerable extent, re- placed t•e rather elaborate and in- volred electrical heating devices. In the cold process of permanent waving the hair is similarly wrapped around a rod of suitable diameter either prior to or after treatment with an alkaline reducing agent such as ammonium thiogl.ycolate. With- out applying external heat, the hair is transformed from its straight state into a desirable undulation. When this has been accomplished, as determined by inspection of test curls, the undulations are perma- nentiv fixed in position bv the appli- cation of a suitable oxidizing agent. This is a brief outline of the process. It will be of interest to discuss each step in greater detail. Prior to giving any permanent wave, but particularly prior to giv- ing a successful cold wave, it is essential that the hair be effectively cleaned. To the uninformed, soap is soap, and all that can be expected from any shampoo is that it re- move the superficial dirt from the hair. But the modern shampoo is much more than just soap, and plays an important role in permanent waving. Any permanent waving process is burdened by many un- controllable variables common to human hair. It is obvious, there-

112 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS fore, that any successful cold wave process must at least eliminate those variables susceptible to con- trol. One of these is the degree of cleanliness of the hair, or the degree of defatting. A good shampoo will obviously remove surface dirt and epidermal debris, and it will also remove to a greater or lesser degree the surface coating of oil or sebum from the hair. Figures 6 and 7 show hair fibers removed from a head before and after an efficient shampoo. But modern syr•thetic detergents go beyond this. Hair or keratin, after all, is not chemically inert it contains many polar groups which can react with anions or cat- 'ions. Thus, Neville and Harris (2) have demonstrated that when sam- ples of wool are soaked in soap solution there is a greater adsorp- tion of cations than there is'of an- ions. Furthermore, Steinhardt, et al. (3) have amply demonstrated in their'studies on the combination of wool protein with acid and base that this is not a simple physical adsorl•tion , but rather that keratins react q•ith anions and cations chem- ically. Similar conclusions x3ere reached by Speakman and Elliott (4) in their studies on the combina- tion of wool with acids and acid dyes. It is evident, therefore, that the action of detergents on hair goes far beyond that of surface cleansing, in that they may combine with and modify the polar groups of the kera- tin, and thus influence the subse- quent action of the chemicals used in the actual waving step. In the cold permanent waving process the hair is divided. into ap- proximately fifty rectangular sec- tions and the hair from each of these Figure &--Hair fiber taken before a shampoo, showing loose dandruff scales. 55 X magnification. Basic fuchsin stain Figure 7.--Hair fiber taken after a sham- poo from the same individual as that in Fig. 6. In this particular fiber the medulla is quite pronounced. 160 X magnification. Basic fuchsin stain