The invention relates to continuous ink jet printing of an aqueous pigmented ink composition recycled from a main ink supply reservoir, employing a printer with a fluid delivery system capable of measuring the ink electrical resistivity, and providing needed quantities of either vehicle replenisher fluid or fresh ink to maintain the desired recycled ink concentration. The electrical resistivity of the pigmented ink can be modified advantageously for stable ink recycling by the addition of the organic amine salt of an acid, and the pH stability of the ink can be simultaneously improved by the additional inclusion of the neutral form of the organic amine in similar molar proportions to the amine salt. The pigmented ink jet ink compositions provide for particularly stable and invariant fluid properties during periods of extended printer operation and ink recirculation.
