What evidence is there that indicates ink is a mixture?

Paper chromatography, simply place a dot from a marker on a strip of filter paper. Then touch the lower end of the paper with the dot about 2 cm above it to a liquid solvent such as alcohol. The liquid solvent will climb the filter paper strip and drag the different colored pigments out of the marker dot, showing that black ink for example may consist of two or three individual colored pigments.

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