An emulsion is a substance that is created by adding two liquids that cannot combine with each other equally. Emulsions are also referred to as colloids wherein one substance will be the dispersing liquid while the other is the one being dispersed. Since the two liquids cannot be equally combined, there is a great tendency for colloids to actually form separate and distinguishable layers after a period of time. A basic emulsion is formed when water and oil is mixed together. Stirring this mixture vigorously may divide the oil into tiny particles as it mixes with water. After some time, the oil particles may start to combine again and form another layer on top of the water molecules.

The behavior of colloids or emulsions in terms of separation or forming several layers is simply due to the fact that the two liquids cannot be equally mixed with each other. This is why some people refer to the process of emulsion as “partial” or temporary. The mixture of two substances is somewhat fleeting and do not last for a long time. At some point, the two substances will find a way to separate from each other and form distinguishable layers. For emulsions to become permanent, some people add a third substance called an emulsifying agent. In the classic example of mixing oil and water, soap for example will help stabilize the mixture and make for a perfect and permanent emulsion liquid. In the case of milk, which is another example of emulsion between milk fat and water, casein is typically added to make this mixture permanent.

The process and concept of emulsion is useful in the manufacture of various household products and even in food processing also. Condiments like vinaigrette are an example of an emulsion liquid with oil and vinegar as the ingredients. With the addition of oil, vinegar is made to taste different making it another type of sauce or condiment. In terms of household items, various cosmetic creams and lotions are made through the process of emulsion for improved consistency and texture.