PHYSICAL PROPERTIES AND STABILITY OF DEAD SEA MUD MASKS 355 Figure 7. Correlation between spreadability and storage modulus value (A) and correlation between spread- ability and stress values at the limit of LVE (B).

JOURNAL OF COSMETIC SCIENCE 356 low shear rate values are the main rheological parameters that can be used to compare different formulations and record the changes during stability studies. The best formulations from all physical criteria and stability aspects were B10G and K5B5G either with [1% and 5% (w/w)] or without ethanol. Their color was dark gray and they had showed no color changes during stability study. They were easily extrudable and had the best spreading behavior for the in-house products. Separation percent was moderate (5–10%), which was considered the best separation percent for mud prepara- tions at initial time points necessary to avoid signifi cant phase separation on storage. In addition, both formulas showed a typical viscoplastic, shear thinning behavior and were fi tted to both models with good correlation coeffi cient. Optimum values of rheological parameters, spreadability, and separation percent are always required, to balance between product stability, aesthetic acceptance, and easy application. ACKNOWLEDGMENT This study was carried out as a part of the MSc thesis research of SS under the super- vision of SH. We acknowledge the support of the Deanship of Graduate Studies in the University of Jordan. SS acknowledges the scholarship she received from the Scientifi c Research Fund at the Jordanian Ministry of Higher Education and Scien- tifi c Research. Figure 8. Correlation between separation percent (w/w) and storage modulus values (A), stress values at the limit of LVE (B), and spreadability values (C).