Patent ID: 7479180

Claim:
An inkjet ink set, comprising: a. a plurality of inks including at least a first and a second ink, each ink comprising an aqueous vehicle; b. a first pigmented colorant dispersed in the first ink and having a pre-determined first polarity; and c. a second pigmented colorant being different than the first colorant and dispersed in the second ink and having a pre-determined second polarity opposite that of the first polarity of the first ink; said second ink initially having an initial polarity similar to that of the first ink and the second polarity is achieved by the addition of a surfactant to the second ink in sufficient amount to reverse the second ink's initial polarity from the initial polarity to the second polarity, said second ink having a first zeta potential at the initial polarity and a second zeta potential opposite that of the first zeta potential, wherein the first zeta potential goes through a zero point before reversing its path to the second zeta potential in a direction opposite that of the first polarity such that the difference between the first and second zeta potential is at least 40 mV, wherein at least one of the colorants of either the first or the second ink is substantially achromatic and the other is substantially chromatic.