PRACTICAL SELECTING METHOD OF WAVE LOTION FOR HAIR DRESSER 49 characteristics cannot be determined using mechanical tests. However, if damage is re- stricted to a decrease in the stiffness or the Young’s modulus after treatment, damage evaluation should be possible by measuring Ero (f/Fo), as previously discussed. Ero is directly related to the set value as shown in equation (5) and it should be empha- sized that in the present study Ero did not simply decrease when Pa increased but abruptly decreased when Pa was approximately 80%, regardless of the wave lotion and the reduc- tion time, as shown in Figure 10(A), which was drawn by plotting the values for Ero vs. the values for Pa listed in Table II. However, these plots with steep declines were obtained only at long reduction times. In order to confi rm this important behavior, therefore, Ero was measured at various Pa values for the A–S, A–N, and C–W lotions as representative wave lotions. As can be seen in Figure 10(B), the abrupt decrease in Ero when Pa was ~80% was observed for the three wave lotions. It should be noted that the existence of this critical point (Pa = 80%) refl ects the point at which hair damage occurs. In addition, it can be imagined that this behavior relates with the characteristic kinetics of TGA-NH4 Table V 20% Index of Virgin Hair in Water at 30°C Japanese senior high school girlsa) Japanese in beauty parlorb Chinesec German ladiesd (45) Parlor-A(8) Parlor-B(7) (6) (8) 61.2 61.0 61.7 61.5 62.2 62.4 62.4 60.7 60.2 62.1 61.1 61.4 61.7 59.1 61.0 62.5 61.9 61.1 61.3 59.6 60.7 62.5 60.9 62.3 61.6 61.7 61.1 61.4 60.4 59.9 60.5 61.9 62.0 61.3 61.2 62.0 62.8 63.4 61.7 61.1 60.2 60.5 60.4 60.9 62.2 61.4 62.5 61.6 61.8 62.0 62.6 62.2 62.5 62.6 61.8 61.7 62.6 62.6 61.7 62.1 61.3 61.2 62.1 62.9 61.5 61.8 61.4 61.9 60.2 62.5 62.1 61.2 61.9 Average of 20% index (%) 61.7 61.6 61.7 61.1 61.0 The total number of virgin hairs, 74 Mean ± SD = 61.6 ±0.8(SD) aDonated by students at Tokyo Metropolitan Toyama High School, Tokyo, Japan. bFrom Parlor A (the beauty parlor “Boy” in Tokyo) or Parlor B (the beauty parlor “ADOMI” in Hachinohe). cPicked up at random from Chinese hair tissue purchased from hair supplier (Deaulax Co. Ltd., Saitama, Japan). dDonated by Dr. S. Roeper in Hamburg, Germany.

JOURNAL OF COSMETIC SCIENCE 50 Figure 9. Relationship between the wave effi cacy measured by a hairdresser and the set in an extensional permanent treatment. (A) Wave effi cacy map reported by a hairdresser. (B) Relationship between the wave effi cacy and the set Sℓ(ext) at 5 min on the Pa/t curves for each wave lotion (See Table IV) correlation: y = 0.263X + 42.491, r = 0.911. (C) Relationship between Pa and the observed set(l) values listed in Table II for the determination of the Sl values shown in (B) correlation: y = 1.158X – 11.662, r = 0.996. described in Characteristic reduction kinetics for the treatment of hair with the NH4 salt of thioglycolic acid. Figure 10 (p. 22). While Ero (f/Fo) can be measured in the laboratory, it is impossible to determine a cus- tomer’s Fo, i.e., the Young’s modulus of the customer’s virgin hair, in a beauty parlor. Fortunately, it was also found in the present study that the 20% index values in water at 30°C for all individual virgin hair samples remained constant at 61.6 ± 0.8%, as shown in