Water-fastness in aqueous ink-jet inks containing water-soluble dyes is achieved by using a specific ionic species having a charge opposite to that on the
dye molecule. Anionic dyes typically contain
sulfonate (or
carboxylate) anionic groups. Using at least one specific ionic species of opposite charge, specifically,
phosphonium salts, causes the colorant components to "
crash" or precipitate out of the water-based ink onto the print medium due to the formation of a suitable charge complex between the ionic parts of the dye and the opposite charge of the counter-
ion species. Other positively charged salts, such as
quaternary ammonium salts, carbonium salts, iodonium salts,
sulfonium salts, and pyrillium salts may be used to improve
aqueous dispersion stability and thus printability. Such additional cationic salt partially replaces the
phosphonium salt(s). Alternatively, certain surfactants, such as aromatic ethoxylates,
polyethylene oxide ethers, or
polypropylene oxide ethers may be used to improve print quality.