A colourant/colour additive (British spelling) or colorant/color additive (American spelling) is a substance that is added or applied in order to change the colour of a material or surface. Colourants can be used for many purposes including printing, painting, and for colouring many types of materials such as foods and plastics. Colourants work by absorbing varying amounts of light at different wavelengths (or frequencies) of its spectrum, transmitting (if translucent) or reflecting the remaining light in straight lines or scattered.
Most colourants can be classified as dyes or pigments, or containing some combination of these. Typical dyes are largely translucent, while pigments are made up of solid particles and are partially or entirely opaque. These properties may change when other common ingredients such as binders and fillers are added, for example in paints and inks. In addition, some colourants impart colour through reactions with other substances.
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