The appearances of small saucer-like depressions in the films surface are caused by particles or droplets of incompatible material. The weight of the particle causes it to sink, but since there is no attraction between paint molecules and molecules in the particles surface, the surface tension of the paint resists the particles entry into the liquid film.

In the zone surrounding the particle, attractions within the paint film pull the surface molecules away from the particle. There is said to be a high interfacial tension between paint and particle.

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To prevent cissing, an additive that reduces interfacial tension is required. When interfacial tension falls, the particle is wetted by the finish and absorbed into the film. Surface-active agents {surfactants) reduce interfacial tension. Alternatively, additives like silicone oil can be added which reduces interfacial tension.

Very little silicone oil is required because it finds its way almost entirely to the surface.

Surfactants are those chemicals whose molecules have two parts of widely differing polarity and solubility. The soaps, for example, have an ionising salt ‘head' to the molecule and a long non-polar hydrocarbon tail.

One end of the surfactant molecule is attracted to polar molecules (e.g. water) and polar surfaces, while the other prefers a non-polar environment. If we have the problem of two materials which will not wet or make chemical contact with one another, surfactants can bridge the gap, interfacial tension will drop and cissing will not occur.

Whenever this bridging is required, surfactants can be used. If pigment surfaces have poor attraction for binder molecules, surfactants can assist dispersion. When two liquids will not mix, surfactants will stabilize droplets of one liquid in the other, i.e. they will emulsify.

Different surfactants are required for different systems and different applications: the nature and properties of the two parts of the molecule will vary from use to use.