Italian salad dressing, image 2 in a series of 2. Italian salad dressing is common in the USA and Canada. It consists of water, vinegar, vegetable oil, as well as spices and herbs. Oil and water/vinegar are immiscible. When vigorously shaken, they form an emulsion (Photo 1). After the container is left undisturbed for few minutes, oil separates from the mixture and floats on top because it is less dense than the water/vinegar solution (Photo 2).