There are a lot of herbal / essential oils on the market, many which are touted as effective against acne:
Volatile essential oils: Tea tree, thyme, eucalyptus, lavender, neem etc.
Non volatile herbal oils (that don't smell): Tamanu, Calendula, Jojoba, Grape seed, Macademia nut etc.
I've seen some clinical trials comparing in vitro efficacy of some essential oils, I believe thyme came out on top against e.g. tea tree, but I'm wondering if anyone here have experimented with pure oils and if, noticed any difference? Between the volatile oils and between the herbal non-volatile ones (which would be fine to use in pure form).
Do you have a study that contrasts them?
Not quite sure what you mean. By "contrast", do you mean the efficacy of Castor in comparison to Camellia or simply which is better of the two?
With that said, there's literally a ton of research papers on both oils and I wouldn't be surprised to find more numerous papers written about their benefits on acne. Just head over to Google Scholar (scholar.google.com) and query, for example, "castor oil and acne".
I use lavender and geranium essential oils directly on face . Geranium is awsome! As i rub it i feel the sebum in my fingers. It uncloggs the pores and it makes gentle scabbing on pimples. Even though i use it undiluted it does not irritate at all. I think its the best for scars, blemishes and even active pimples!!
Oh, i forgot NEVER trust castor oil. I used it for 3 days and it broke me out like hell. Thank god i quit on time from it