342 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Ordinary Light Polarized Light 99 Days 16 Months No Agglomerates 16 Months With Agglomerates Figure 3. Destabilization of the model cream.

CONSISTENCY DEVELOPMENT OF A MODEL CREAM 343 cream transforms into the unstable state of an emulsion droplet suspension. Further, after this transition to the suspension state, the lipophilic gel phase (also known as coagel) still surrounds the dispersed internal phase. The agglomerates and oil droplets in the photomicrographs of Figure 3 indicate that the wax and oil components of the internal phase form distinct entities when phase-separated. According to both Eccleston (1) and Junginger (8), pearlescence in creams is attributable to crystallization in the continuous phase in the form of light-refracting platelets. Junginger (8) further states that these platelets are structurally similar to lipophilic gel phase (i.e., coagel). In the case of the model cream discussed here, the phase-separated wax components are re- sponsible for the pearlescence in the 16-month-old sample. IDENTIFICATION OF PHASE-SEPARATED COMPONENTS In order to further identify the phase-separated components, thermal optical videomi- croscopy was performed on the 16-month-old cream using slides specifically selected to have minimal or extensive agglomeration. Figure 4 shows the photomonitor recordings of the melting transitions of 16-month-old cream samples from slides with and without extensive agglomeration. The slide with relatively few agglomerates forms a smooth transition to an initial arrest at 45øC followed by a final arrest at 48.5øC. The videotape of the melting transition indicated that these arrests correspond to the melting point of the cream matrix and trace amounts of agglomerate, respectively. The initial arrest in the slide with extensive agglomeration occurs at the same temperature as the slide with trace agglomerates and, according to the videotape, also corresponds to the melting point of the cream matrix. A broad transition in the photomonitor recording occurs over the range from 47øC to 58.5øC. The videotape indicates that this corresponds to the agglomerate melting transition. Examination of the formula indicates that the agglom- erates could be cetyl alcohol, cetyl palmitate, and/or stearyl alcohol, which have liter- ature melting points at 49øC, 54øC, and 56-60øC, respectively (10). The values at the 90 80 70 60 50 40 30 25 Temperature øC Figure 4. Photomonitor recordings of the model cream: (a) model cream with few agglomerates (b) model cream with agglomerates.