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Types of common colloids

Continuous phase	Dispersed phase	General name	Example
Gas	Liquid	Aerosol	Fog, mist, fine sprays
Gas	Solid	Aerosol	Smoke
Liquid	Gas	Foam¹	Soap foam
Liquid	Liquid	Emulsions, micro-emulsions²	Cream
Liquid	Solid	Sols	Paint
Solid	Gas	Solid foam	Polyurethane
Solid	Liquid	Gel³	Bitumen
Solid	Solid	Composite material⁴	Composites, ceramics

¹In a foam (soap foam, for example), the dispersed particles may not be small. But still it falls in the category of colloids because it is interfacial phenomena that are important in such a case.

² Micro-emulsion is a dispersion in which the dispersed particles have the size of the order of a micron.

³ Liquid particles trapped in solid matrix.

⁴ To obtain an even distribution is a point of concern in composite materials.

Are alloys colloids?

Alloys are solid solutions (i.e. homogenous) of two or more metals. The homogeneity implies that such solutions are not a part of colloidal phenomenon. A colloid should necessarily have two discernible phases, but in alloys the metals are indistinguishable from each other.