J. Cosmet. Sci., 69, 371–382 (September/October 2018) 371 Quantifying Hair Motion TREFOR A. EVANS and SEBASTIEN BREUGNOT, TRI-Princeton, Princeton, NJ (T.A.E.), Bossa Nova Technologies, Culver City, CA (S.B.) Synopsis A commercially-available instrument, previously intended to visualize and quantify hair shape and volume, has been modifi ed to measure hair motion. Specifi cally, a transversal motor now induces a side-to-side oscillating tress stimulus, while a video camera records the outcome. Image analysis software allows for quantifying the amount of motion (i.e. the amplitude), the shape and volume of the hair during motion, and the homogeneity of the hair (i.e. bulk –vs- fl yaways). Each of these parameters has considerable dependence on the frequency of oscillation and so evaluations are carried out by systematically varying this parameter. Preliminary validation experiments are documented which involved methodical variation of parameters that were presumed to be of importance. These included the size and shape of hair tresses, various hair treatments, and environmental conditions. As a result of the sizable amount of data that results, graphical depictions provide the best means of representation. For example, amplitude –vs- frequency plots describe the extent of hair motion as a function of energy supplied to the system. Visually noticeable decreases in tress motion were observed after applying small quantities of silicone oil to the hair. This occurrence reduced the measured amplitude of tress motion, while also moving the maximum amplitude to high frequency. Accordingly, it is supposed that improved motion is attained by inducing a higher amplitude at a given frequency, and/or by attaining comparable amplitude under the application of a lower frequency. INTRODUCTION During virtually every TV commercial for hair care products, a model is shown whose hair moves in a beautiful, fl uid, fl owing manner. Clearly, this motion is a signifi cant factor in the perception of attractive hair yet, this topic has received relatively little attention in the scientifi c literature (1). Even with primitive experimental set-ups, it is easily seen that different “hair types” do indeed move quite differently. Asian hair moves differently from Caucasian hair straight hair moves differently from curly hair virgin hair moves differently from chemically dam- aged hair. The issue becomes how to quantify this process and describe motion in terms of numbers. In this work, we report on modifi cations to a commercially available device (previously intended to quantify the shape of static hair tresses) to visualize and analyze hair motion. Address all correspondence to Trefor A. Evans at tevans@triprinceton.org.

JOURNAL OF COSMETIC SCIENCE 372 In validating any instrumental method, it is desirable to conceive of means for system- atically manipulating the desired variable to ensure that predictable responses result from such logical changes. Thus, it is necessary to contemplate which physical properties of the hair might provide impact. Hair weight would seem a contributor—where higher weight may be a result of fi ber thickness, length, and/or density on the scalp. Hair stiffness would seem a factor, as would curvature and interfi ber friction. It is noteworthy that these exact same parameters have also been suggested to be key components of hair body and volume (2,3). Therefore, these attributes are seemingly related and it is hoped that learnings from studying hair motion may provide much needed insight into these two other ambiguous and poorly understood variables. EQUIPMENT BOLERO® by Bossa Nova Technologies (Culver City, CA) is a commercially available instrument that allows for visualization and quantifi cation of the 3D shape and volume of hair tresses. A digital video camera is used to procure photographs of hair tresses under precise mounting and lighting conditions. The tresses are also automatically rotated to provide 360° visualization of hair shape. Another feature involves a back fi eld illumination source which highlights and differentiates wispy, fl yaway fi bers from the tress bulk. Image analysis techniques subsequently allow for quantifi cation of tress shape and volume, while also providing a means for evaluating relative propor- tions of these frizzy fi bers (see Figure 1). Details of this device have been described elsewhere (4). In the present work, this existing setup has been modifi ed to visualize and analyze tress motion. The rotational mechanism of the original instrument was replaced by a transversal motor that induces a side-to-side oscillating tress stimulus. In the present form, frequencies in the range 0.5–2 Hz can be selected. Similarly, the camera was replaced by a digital Figure 1. Image analysis for evaluating hair volume and fl yaway using Bolero® from Bossa Nova Tech.