They are used in small quantities, but their role is essential to obtain the optimal results.
They can be:
Their role is to assist in the process of dispersing and grinding, to obtain particle size that is close to the basic constituent particles of the pigments and fillers that are used. They thus help to destroy the aggregates and agglomerates of particles of the pigments and fillers. Their selection and precise metering are vital to development of the correct hue. Thus the colour strength of pigment can be optimized. The selection and dosage of dispersing agents are specific for each pigment or mixture of pigments.
Dispersants are also intended to retain good dispersion of particles of pigments and fillers, over time. In their absence, these particles tend to agglomerate, when the physical restraint that has separated them is removed.
Their role is to modify the viscosity and rheology of paint to achieve good conservation properties (prevention of sedimentation) and ability to obtain the desired application technique (brush, roller, knife painting, ...).
They can be derived from natural products (gums, smectite, cellulose derivatives).
They may also be made of synthetic polymers.
They are often used in combination, and in all cases, they are essential to a good formulation.