Raw material Paste 1 White petrolatum Paraffin oil Stied Lan N Propyl paraben Glyceriyl stearate Propylene glycol (PG) Methyl paraben Dead sea salt Glycerin Preservative RO water DEAD SEA SALTS IN COSMETIC EMULSION Table I Fomulation of the Body Cream Used in the Study wt% 4.0 4.0 4.0 4.0 4.0 0.1 4.0 4.0 0.2 3 0.0-0.25 7.0 0.2 Up to 100 Na+ (25600 mg/kg), Ca+ 2 (2000 mg/kg) and Cl- (382100 mg/kg). The complete chemical analysis of the DS salt used can be found in reference 8. CREAM PREPARATION The body cream was prepared by adding the oil-phase components and water-phase components at room temperature into two separate jacketed glass vessels. Hot water was circulated into the jackets of the vessels to attain the required temperatures. In order to dissolve all the water- and oil-phase components, the water phase was heated to 75 ° C, and the oil phase to 80°C under high-speed agitation. The mixing speed was 700 rpm for both the oil and the water phases. When the water and oil phases reached 75 ° C and 80°C respectively, the water phase was added to the oil phase and the resulting emulsion allowed to cool down to 40°C under slow-speed agitation (400 rpm). The preservative was added at approximately 40°C and the agitation was discontinued. The cream samples were stored in glass beakers at three temperatures: 8°C, room temperature, and 45°C. The rheological properties of the prepared creams were measured at different storage points during a four-month period. In addition to the conductivity measure­ ments of the cream samples, the stability of the prepared creams was investigated using a centrifuge after six weeks from the time of preparation. In order to investigate the reproducibility of the sample preparation, part of the samples was prepared in duplicate. METHODOLOGY Experiments were performed to study the rheology and stability of the body cream prepared in the laboratory. Rheological studies of the body cream included the study of the dependence of apparent viscosity on shear rate. DS salt concentrations varied from 0.0 to 0.25%. Salt-free cream was used as a control sample, and other samples containing DS salt were compared to this control.

4 JOURNAL OF COSMETIC SCIENCE EQUIPMENT Rotational viscometer. All rheological measurements of the body cream samples were car­ ried out at 25°C using a concentric cylinder viscometer (Haake VT 500, SVl-system). The viscometer has an inner cylinder rotating in a stationary outer cylinder. The SVl­ system has a bob with a length of 61.4 mm and a radius of 10.1 mm, and it has a jacketed cup with a radius of 11. 5 5 mm. Body cream samples were placed in the temperature-controlled measurement viscometer and equilibrated to 25°C for ten min­ utes prior to performing the measurements. The rheological experiments were carried out in duplicate and the reproducibility was ±4% on average for selected samples. Centrifuge. All stability tests of the body cream samples were carried out using a con­ ventional centrifuge (Hettich Zentrigugen, Germany). Samples were subjected to an accelerated stability test using the centrifuge at 4000 rpm for 30 minutes six weeks from the day of preparation. Conductivity meter. Conductivity measurements of the cream samples were performed with an electrical conductivity meter (Euteoh, Cybercsan 1000, Singapore) at room temperature at different storage periods of four months. Stirrers. A three-bladed impeller was used to mix the oil phase of the cream during preparation (Heidloph, RZR, Germany). It was driven by a variable-speed motor (400- 1400 rpm). A two-bladed impeller (Stuart Scientific, SS2, U.K) set at 700 rpm was used for mixing the water phase during cream preparation. RESULTS AND DISCUSSION CENTRIFUGE TEST The first body cream stability test was carried out using a centrifuge. Samples were subjected to accelerated stability testing using a centrifuge at 4000 rpm for 30 minutes six weeks from the day of preparation. The aim of this test was to check for phase separation and to examine how homogenous the prepared cream was. Results indicated that all cream samples containing 0.25 wt% of DS salt or less were homogenous, and no change in the sample structure was observed. Samples containing more than 0.25 wt% of DS salt showed a phase separation pre- and post-centrifugation. For this reason, the rheological analysis was limited to the stable samples. RHEOLOGICAL PROPERTIES In this part of the investigation, the effect of added DS salt on the viscosity of the body cream samples was examined by adding different salt concentrations to the standard formula mentioned earlier in the Experimental section. The concentration of the DS salt varied from 0.0 to 0.25 wt%. Creams containing more than 0.25 wt% DS salt were completely unstable. The effect of DS salt concentration on the apparent viscosity of cream samples stored for one week at room temperature is shown in Figure 1. As can be seen in this figure, the effect of increasing the DS salt concentration from 0.0 to 0.25 wt% on the apparent viscosity can be divided into four regions. In the first region, a decrease in the apparent