Hi dear, my name is Sabah and I am working on face lotion that Has 7 different oils using shea butter as a base cream. My theme is to use strictly natural oils. I noticed that in hot weather the cream melts and some oil seperates. How can I make my mixture stable? And whether I can use a natural preservative within this mixture? Also i will appreciate it if u guide me into which iul is high in vitamin C which I can add to my formula. Thank you in advance.. Sabah