The primary purpose of the thin film applied to a surface is protection and/or decoration. The film is relatively thin, whereas the object to which it is applied is massive in comparison. The definition of this thin film as a coating carries with it the implication of function and purpose. Design parameters for coatings include initial preapplied form, application technique, and final appearance and function. The composition of the coating may be simple (a single chemical) or may be a complex formulation of a variety of materials, each having a specific function. Formulations generally have three components intended to be relatively permanent and serve specific functions in the final film. These permanent components are pigment, vehicle, and additives. Pigment provides colorant or other functions. The vehicle, sometimes called the binder, acts as the adhesive to stick pigment particles to substrate or to each other. Finally, additives are chemicals that modify the properties of the coating in fluid or solid state. A fourth, ephemeral, component may be in the coating formulation before application: the carrier fluid, which evaporates after application to allow the fluid residues to become immobilized.
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