Testing Essential Oils

I have been working on finding the best natural oils for the Sweet Potatos babies' aroma. I want a recipe that lasts long and is safe for microwaving. So far, I've got a eucalyptus/peppermint blend, a lemongrass/white tea blend, and a passion fruit blend. I'll be posting an aromatherapy chart on the Sweet Potatos page for homeopathic reference.