Hi. You might have better luck if you post this in the bath and body section of the forum. I'm no expert, but to answer your question, lotion bars are made from waxes and oils and have no water added so you don't need to add preservatives. Generally the ratio is 1/3 wax, 1/3 butter (cocoa, shea, mango, etc.) and 1/3 liquid oils. You melt the stuff together and pour. If the consistency is too hard or soft, remelt and tweak, until you will get something you like. There are more threads on this topic in the bath and body section, as I mentioned. Good luck to you. I love lotion bars!
