Coating is used to finish paper and provide some added-value:
Coating is a process by which paper or board is coated with an agent to improve brightness or printing properties. By applying PCC, china clay, pigment or adhesive the coating fills the miniscule pits between the fibres in the base paper, giving it a smooth, flat surface which can improve the opacity, lustre and colour-absorption ability. Various blades and rollers ensure the uniform application of the coating.
Different levels of coating are used according to the paper properties that are required. They are divided into light coated, medium coated, high coated, and art papers - art paper is used for the high quality reproduction of artwork in brochures and art books.
Not all paper is coated. Uncoated paper is typically used for letterheads, copy paper, or printing paper. Most types of uncoated paper are surface sized to improve their strength. Such paper is used in stationery and lower quality leaflets and brochures.