A tribometer was developed to simulate friction phenomena occurring when human fingers are rubbed together in order to acquire the tactile sensation of applying cosmetic foundation. The tribometer utilizes silicone-rubber surfaces with compliance comparable to that of human fingerpads; these surfaces are lubricated by 10 types of samples simulating cosmetic foundation. To characterize the samples, seven types of feature quantities are introduced from friction signals acquired in three types of sliding tests. The relationship between feature quantities and tactile sensation was investigated using a multiple regression analysis; resulting equations show some level of agreement with the score of a sensory assessment vis-a`-vis five types of tactile sensation. The results indicate that static and kinetic frictions are not always dominant factors in determining the comfort of tactile sensation in applying cosmetic foundation.

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When we acquire tactile sensation, contact and relative motion are necessary between our bodies and objects. This implies that the tactile sensation is produced by friction phenomena. The present paper describes the sliding test for estimating the tactile sensation associated with cosmetic foundation. When the cosmetic foundation is rubbed with an apparatus that imitates a human finger, two types of time-evolving signals -normal and tangential -are obtained as the source of the tactile information. In the sliding test with the apparatus under the frictional condition of humans acquiring the tactile sensation, frictional vibration is observed in the tangential signals, which should be related to the tactile sensation associated with the cosmetic foundation. When a surface with a grooved pattern that imitates fingerprints is used in the sliding test, two types of frictional vibrations are observed. If an adequate sliding velocity is selected, the slight difference between the four types of commercial cosmetic foundations is discriminable by using the signals of these vibrations.

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