j. Soc. Cosmet. Chem., 44, 299-318 (November/December 1993) Gloss of hair surfaces: Problems of visual evaluation and possibilities for ooniophotometric measurements of treated strands W. CZEPLUCH, G. HOHM, and K. TOLKIEHN, Bundesanstalt fiir Materialforschung und -priifung, Berlin ( B AM ) ( W. C . ), and Hans $chwarzkopf GmbH, Hamburg (G.H., K.T. ), Germany. Received April 6, 1993. Based on two presentations at the 8th International Hair Symposium, Kiel, Germany. Synopsis A great number of products are offered on the hair cosmetics market that, in addition to their basic benefit, aim to improve hair gloss. Gloss can be regarded as a special optical property for the description of apparent decorative qualities and for the analysis of surface properties of hair. As it is very complex, no simple relationship exists between the appearance of gloss and the light reflected from the hair. But up to now, investigations made on various materials suggest the spatial distribution of reflected light, the indicatrix, as being very important. Therefore, hair indicatrices were measured using a precise goniophotometer. The resulting data had to be compressed, both for easier handling and for the description of significant aspects of the visual gloss impression. Two indicatrix parameters are regarded as "gloss criteria": the improvement of gloss is related to an increasing amount of maximal reflected light and a decreasing half-value angle, which means the spread of reflected light in different angular directions. The reproducibility and the precision of these measurements required an air-conditioned test room, an optimized preparation technique including the construction of a special sample holder for the hair strands, and the minimizing of the variance between the strands by always comparing the indicatrices of the untreated and the treated samples. The strands were treated with various hair cosmetics, e.g., hair sprays, lacquers, rinses, care sprays, as well as glazes and hair gels. To check the correlations between the results of the objective measurements and the visual gloss inspection, several gloss evaluations were made in a "gloss matching booth." INTRODUCTION Research on gloss has been published for more than 100 years (see list in reference 1), but very little relates to the gloss of hair (2-4). Therefore, it might be of use to consider this problem in a more general way. 299

300 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS The International Commission on Illumination (CIE) defines the current state-of-the-art for gloss as "the mode of appearance by which reflected highlights of objects are perceived as superimposed on the surface, due to the directionally selective properties of that surface" (5). This definition is not quite satisfactory, but it is the minimum consensus, and it shows at least a clear connection between gloss and preferred reflection of light by the tested sample into the specular direction. Additionally, it indicates that the term "gloss" is reserved exclusively for the visual sensation and that measured related data have to be indicated differently, for example by word combinations like "specular gloss" in ISO 2813 (6). Stamm et al. (2) mentioned in their study that "goniophotometric curves of hair strands do not provide results as precise as those obtained from monolayers of parallel oriented fibers." They decided to design and make a rack on which a number of fibers could be strung. Normally they worked with an arrangement of 21 single fibers. On styled hair, however, the hair fibers are not arranged next to one another in parallel and exact distances but one on top of the other in several layers and also touching one another. Especially with tests of sprays and hair lacquers, the appearance of a polymer film is influenced by its distribution on the hair. The distribution itself depends, to a large extent, on the position of the hair fibers, i.e., how closely single hair fibers lie next to each other or one behind the other in a tress of hair and what capillary and interfacial forces are activated. Moreover, the strands had to be prepared so that, on the one hand, they could be well compared with each other, i.e., that they were provided with a very good homogeneity, and, on the other hand, that they allowed successive shampooing and drying without being disarranged. A loss of the initial arrangement or a displacement of the sample in the measuring device would mean a falsification of the measurement compared with the original measurements (see CHARACTERIZATION OF THE PHOTOMETRIC DATA below). We therefore constructed strandholders to fix the prepared strands in the goniophotometer (see SAMPLES AND THE PREPARATION OF SAMPLES be- low). Statistics were also one reason to test on a large hair collective. From a larger surface we expected to obtain a practical averaging and a more even basic measuring curve for our before/after comparisons. Actually, it was the aim of our studies to test hair cosmetics and raw materials under conditions of use. But we did not want only to obtain qualitative results but also criteria for a quantitative assessment of the hair gloss. During our work we always compared measured results and subjective evaluations. First results of our measurements showed that the gloss of undamaged black hair could not be improved by products such as gloss sprays obtainable in the free market. We verified this result on a suitable model in a half-side test and finally we came to the same conclusion. We therefore decided to damage test strands in order to achieve a gloss improvement by the use of products. VISUAL GLOSS EVALUATION Wundt, one of the earliest researchers, published his results in 1861 (7). At that time,