The new Pestle & Mortar Vitamin C 2-Phase Serum (£68) got it's name from the fact that inside the bottle are actually two separate chambers: one that contains a vitamin-C-rich water and the other a superlightweight oil. When you pump the bottle, the two separate phases mix together, meaning that the vitamin C in the serum (well, actually, there are three different forms in this formula) is in its most powerful state when applied to your skin. As for what's in the oil? That would be tamarind and pumpkin extracts, which also help to clarify and brighten your complexion.