JOURNAL OF COSMETIC SCIENCE 380 that of any product/treatment. For this reason a meticulous tress treatment and drying process is necessary in this work. TRESS SHAPE DURING MOTION The various aforementioned treatments and conditions can also affect the shape of the hair during motion. For example, in the previously described experiment involving the infl u- ence of relative humidity (see Figure 7), hair equilibrated at high humidity appeared decidedly more “puffed up” in comparison with the low humidity state. As a further ex- ample, heat straightening greatly decreases the technical volume of the hair because of the extremely straight and highly aligned nature of the fi bers. Such measurements represent the fundamental objective of the original BOLERO instrument, although here analyses can be further performed frame by frame on videos of moving hair (see Figure 9). As described earlier, the software is able to calculate an overall tress volume— however, via the backlighting approach, this total volume can be deconvoluted into a bulk volume and a volume of wispy fl yaway fi bers. Thus, all of these parameters can be tracked during the oscillating motion. Again, there is complexity to this process. The moving hair experiences differing degrees of momentum as it traverses the oscillating pathway. For example, the fi rst image in Figure 8 (frame #0) shows hair concave to the left-hand apex of motion as it moves to the right. The reverse scenario would occur soon after frame #20 as hair returns from the Figure 8. Reproducibility in the shape of amplitude versus frequency plots.

QUANTIFYING HAIR MOTION 381 right-hand apex. Thus, tress shape, volume, and the homogeneity can vary during this motion. Furthermore, frequency also has a major impact on the momentum magnitude. SUMMARY/CONCLUSIONS Earlier it was noted that relatively little work has been performed in the area of hair motion. Our foundational work perhaps sheds light on this defi ciency by highlighting the com- plexity of the topic. Existing commercial equipment has been modifi ed to provide a means of controlling hair motion, for video capture and manipulation, and to provide subsequent image analysis capability. However, even with this powerful device, the com- plexity of the task in hand is still formidable. Using this equipment, we have performed systematic experiments to primarily study the amplitude of hair tress movement when oscillated in a side-to-side motion. Sizable changes in this property can occur as a function of hair treatments, experimental test conditions and considerations related the size and shape of the hair tresses being used. The nature of this motion is strongly dependent on the oscillating frequency—although the manner of this frequency response varies with the aforementioned considerations. Therefore, experiments performed at different single frequencies are very likely to produce different ranking of samples. Accordingly, we advocate the generation of amplitude versus fre- quency curves—which involve progressively and systematically increasing the oscillating frequency. The relationship between frequency and energy allows for conceptualization of hair move- ment in terms of the amount of motion attained as a function of energy input to the system. For example, visibly diminished motion as a result of silicone oil treatment is accompa- nied by both a reduction in the motion amplitude and an increase in the frequency neces- sary to produce this motion (i.e., lesser motion, even though additional energy is being supplied to the system). Conversely, it can be suggested that improved movement might involve enhanced motion for a given energy input, and/or comparable motion for less energy input. Figure 9. Analyzing hair shape and fl yaway during motion.