I LOVE adding essential oils! Peppermint is very good, it's in the original No-poo formula. At the moment I'm adding lavender, which is very soothing. I've also tried making the cleansing Co with jojoba oil, which was fine, but a little too heavy for my fine hair
Lecithin is very good for the hair, but it comes from eggs, which are a protein, so if your hair is protein-sensitive, be careful. i know mine got a little dry when I tried adding this. i haven't tried stearic acid yet, let me know how it turns out! Also, how long does the rosemary oil preserve for? i am interested in trying it.