Oil & vinegar

Vinaigrette is made by mixing an edible oil with a mild acid such as vinegar or lemon juice (citric acid). The mixture can be enhanced with salt, herbs and/or spices. It is used most commonly as a salad dressing, but can also be used as a marinade. Traditionally, a vinaigrette consists of 3 parts oil and 1 part vinegar mixed into a stable emulsion, but the term is also applied to mixtures with different proportions and to unstable emulsions which last only a short time before separating into layered oil and vinegar phases. Vinaigrette is the diminutive form of the French word vinaigre ("vinegar"). It was commonly known as "French dressing" in the 19th century. In general, vinaigrette consists of 3 parts of oil to 1 part of vinegar whisked into an emulsion. Salt and pepper are often added. Herbs and shallots, too, are often added, especially when it is used for cooked vegetables or grains. Sometimes mustard is used as an emulsifier and to add flavour.

Source: Wikipedia