AS A MASK:
Step 1: Soak a cotton pad in Milk of Magnesia, and apply to any oily areas, as thickly as you can.
Step 2: Leave to dry for 10-15 mins.
Step 3: Rinse off with warm water and pat dry. You'll find that all the oil as disappeared!
AS A FOUNDATION PRIMER (or used alone):
Step 1: Place a cotton pad over the bottle top and quickly tip over, so you get a small amount of Milk of Magnesia on the pad.
Step 2: Apply to oily areas (ie. forehead, nose) thinly.
Step 3: Leave it as it is, or put foundation on top. This is great for preventing oil.