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An emulsion is a stable and homogenous mixture of two liquids which do not normally mix (they are immiscible between themselves), such as Vegetable oil and water. Common examples are milk, mayonnaise and cutting fluid for metalworking. Emulsions can be true colloids or less stable mixtures, such as salad dressing (a mixture of balsamic vinegar and olive oil), which tend to separate in a short time. Changes to the suspending liquid, such as thickening salad dressing with the addition of mustard, helps to hold the suspension much longer.

An emulsion can be broken down (i.e. the liquids separated) by factors such as mechanical manipulation (as in a milk churn), chemical effects (as when milk is curdled by the addition of vinegar), and time.

An emulsifier is a substance which aids the formation of an emulsion. Often listed as a food additive, it usually works by thickening the mixture. Another type of emulsifier is detergent, which will bind to both oil and water, thus holding microscopic oil droplets in suspension. This principle is exploited in washing-up liquid to remove grease from plates, etc.

Emulsification' is to emulsify, to form an emulsion.

An emulsion paint (often abbreviated to emulsion) is a water-based paint commonly used for painting indoor surfaces. Emulsion paints are also known as latex paints. It is so called because the polymer is formed through an emulsion polymerization whereby the monomers were emsulified in a water continuous phase. The polymer itself is not soluble in water and hence the paint is water resistant after it has dried. Residual surfactants in the paint as well as hydrolytic effects with some polymers cause the paint to still be susceptible to softening and, over time, degradation by water.