A colored marker ink for use on a writing board is manufactured by blending a colorant, a resin and a mixed solvent consisting of a good solvent for the resin possessing a high speed of vaporization and a non- solvent for the resin possessing a lower speed of vaporization than that of the good solvent. When a letter or figure is written on the board with this marker ink, the resin component of the ink thus applied to the board gels into opaque lines in the shape of the letter or figure in consequence of gradual vaporization of the good solvent.
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