Polymeric dye

Red polymeric dyes of the anthraquinone series of the formula: are particular useful as non-absorbable dyes for edible goods. In the formula I: R1 and R2, which are identical or different, are hydrogen atoms, halogen atoms of atomic number 9 to 53, alkyl or alkoxy groups of 1 to 3 carbon atoms, nitro groups or sulphonate groups, R3 is hydrogen or an alkyl radical of 1 to 3 carbon atoms, B is an organic polymeric main chain which is bonded to the nitrogen atom via a covalent bond, which is practically free of crosslinking and contains only covalent bonds which are stable under the acetic, basic and enzymatic conditions of the gastrointestinal tract of humans and other mammalian species, and n is from 10 to 4000.