Ink-jet ink sets, pigment-based ink formulations, methods of printing, and methods of enhancing print quality, are disclosed. One exemplary ink-jet ink set, among others, includes a pigment-based ink formulation at a first pH, including: a pigment, and an amphoteric dispersant having an isoelectric point; and a second ink formulation at a second pH, wherein the first pH and the second pH are each selected from an acidic pH and a basic pH, wherein the first pH and the second pH are not the same, and wherein the amphoteric dispersant has a higher isoelectric point than the first pH when the dispersant is acidic, and a lower isoelectric point than the first pH when the dispersant is basic.