JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS :' / Figure 3. Tactile assessment of greasiness. Facing page 8

SENSORY PERCEPTION AND EVALUATION OF HAIR GREASINESS 9 to touch them. Lighting conditions were chosen to avoid highlights on the hair, so that gloss variations were not visible and the predominant visual cue to greasiness was the 'rats-tails' effect. The test design was similar to that for the tactile assessment, except that the panellists ranked three switches at a time. By analysis of the data from these tests in the way described earlier, it was possible to assign numerical values to each of the eleven materials on a scale of greasiness, either tactile or visual. If these scale values are considered in relation to the subjectiye order of consistency of the materials, a general pattern begins to emerge (Fig. 4). We see that the tactile greasiness is low for the thinner oils, increases to a maximum with the semi-solids, and decreases again as the materials become harder and waxier. The visual greasiness pattern, on the other hand, is more complex, and it is interesting that over part of the range (LAN to LIP II) the visual greasiness appears to increase with consistency at the same time as the tactile greasiness is decreasing. These relationships became clearer when the rheological characteristics of the materials were quantified instrumentally. Over such a wide range of materials, no single rheological parameter can serve as the basis for com- parison, but it was found possible to use a minimum of two parameters. The oils were characterized by viscosity measurement with a Ferranti- Shirley cone-and-plate viscometer, while for the solids and semi-solids a -2 -3 -4 Tactile \ b ! i I i d SIL SIL I 2 I I I I I I I I I SII_ SIL LAN PJ PEG LIP LIP LIP WAX ..3 4 I ]-J Trr Rank order of increasing consistency Figure 4. Sensory greasiness vs subjective consistency.