8 JOURNAL OF COSMETIC SCIENCE Storage condition: room temperature 30 5 0.3 Shear rate= 12.37 (1/s) 100 Salt concentration (w/w % ) 0 0 Storage time (day) Figure 4. The effects of DS salt concentration and storage time on the apparent viscosity of cream samples stored at room temperature. rn rn 2.00 -.--------------,----.--------r------.-------, 1.50 Storage conditions: room temperature Salt content= 0.0% Salt content= 0.15 % _9 1.00 ---""----------1--------1----�::.......J....-----+------+-------I 0.00 -1£....------t-----+------+-----+------+-------I 0 40 80 120 Storage Time (day) Figure 5. Weight losses in cream samples as a function of storage time.

DEAD SEA SALTS IN COSMETIC EMULSION 9 Aranberri et al. (10) found that in emulsion systems with added salt, water evaporation virtually ceased before all the water present was lost, probably as a result of oil-drop coalescence resulting in the formation of a water-impermeable oil film at the emulsion surface. A control experiment was conducted on a sample placed in a closed container where no change in weight was observed. In addition, the viscosity of this sample did not show significant change. This result supports our previous hypothesis that the increase in cream viscosity with storage time is caused by the evaporation of water from the emulsion. The samples containing 0.07 and 0.15% DS salt showed a maximum viscosity over the entire range of storage time tested. With the increase in storage time, the two maxima showed less increase in apparent viscosity than in the salt-free sample. EFFECT OF STORAGE TEMPERATURE In this part of our investigation the effect of storage conditions was studied. Body cream samples were stored up to four months at (i) room temperature, (ii) 45°C, and (iii) 8 ° C. The concentration of the Dead Sea salt varied between 0.0 and 0.15 wt%. Figure 6 shows the effect of storage temperature on the apparent viscosity of the cream samples stored for one week. An increase in the apparent viscosity at constant shear rate with increasing storage temperature can be clearly observed. The increase in the viscosity of -en 'ui en · � a. a. 20 18 16 14 12 10 ., ...... .. .. .. .. .. ' , , ______..- •,_EEi- .......---········ Storage time = one weak Shear rate= 7.387 (1/second) * EE ■ 8 °C room temperature 45 °C 8 ----l----�--�--.l,-------,--------,----'---r----,----------'j 0.00 0.04 0.08 0.12 Salt concentration (w/w%) 0.16 Figure 6. The effect of DS salt concentration on the apparent viscosity of cream samples stored for one week at different temperatures.