The invention relates to a method for controlling the ink quality of an ink jet printer, during printing, the printer comprising at least one ink reservoir (11) and a solvent or diluted ink reservoir (12), a print head (50) and a supply circuit for sending ink and/or solvent to the print head, method in which: a correction volume of solvent, or diluted ink, to add to the ink to compensate a variation in viscosity of the latter is estimated; and a plurality of elementary quantities of solvent, or diluted ink, separated by ink, is sent to the print head, each of a volume comprised between 0.1 cm3 and 5 cm3, the sum of the elementary quantities of solvent, or diluted ink, being substantially equal to the correction volume to add.