Abstract: Pigments that have been at least partially treated to form surface-attached functional groups are combined with long chain amine oxides in an ink-jet ink to provide waterfastness. The ink-jet ink for ink-jet printing comprises: (a) a vehicle comprising (1) 0 to about 30 wt % of at least one organic solvent, and (2) 0 to about 30 wt % of at least one water-soluble surfactant, and (3) about 0.1 to 10 wt % of at least one zwitterionic surfactant; (b) about 1 to 20 wt % of at least one chemically-modified, water-soluble macromolecular chromophore comprising a pigment having functional groups covalently attached thereto; and (c) the balance water. The inks of the invention evidence increased waterfastness with the presence of the zwitterionic surfactant, yet other properties, such as decap, kogation, and edge acuity, are not adversely affected by the presence of the zwitterionic surfactant. Indeed, decap and edge acuity are improved by the presence of the zwitterionic surfactant.