Re-posting my answer to this question, because I do get it quite a lot. Just to clarify, when I said in my "DIY stuff to never try" video that I don't support using ACV as a toner, I meant that it's not a good idea to use it at 100% concentration, not that I don't think it's a valid or worthwhile ingredient overall. It's not like lemon oil and lemon juice, which never belong on the face at any concentration. I don't object to using diluted ACV--a lot of people really love ACV, and it can have very beneficial actions. Just keep pH in mind, and dilute it with water. If you want to use it as a toner, dilute it about 50/50, in a mask, about 67/33 (acv/h20) or 75/25, and as a spot tx, about 75/25.
Q: I know you advise against using apple cider vinegar on the face, but what about using it with aztec clay? I've heard it's popular for this specific type of clay because otherwise it will not spread across the skin. Also:http://www.reddit.com/r/SkincareAddiction/comments/1b416l/the_science_and_history_of_apple_cider_vinegar/
A: It's a pH issue, so knowing a bit of chemistry is helpful here. The pH of bentonite clay is high while the pH of ACV is low, so when you mix them together, you'll get that classic chemistry class effect of fizzing and bubbling. This raises the pH of the ACV (while lowering the pH of the clay), making the pH less of an issue. However, I still recommend diluting the ACV with a little bit of water, maybe 3:1.
FutureDerm recently uploaded a video talking about this (I don't know where their old article went, but this covers the same info): buff.ly/1mRfaG2