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Top image: two liquids separated into two layers (no emulsion). Bottom image: droplets of one liquid mixing with the other liquid (emulsified).

Two separate liquids will not always mix, for example oil and water forms two separate layers if added to one another. However if oil and water are shaken together, droplets of one liquid will mix into the other. This mixture is called an emulsion.

An emulsion is a type of colloid.

Common examples of emulsions include paint, milk and ketchup, which can all be classed as various oils suspended in water.