A water-in-oil emulsion ink comprises a water phase and an oil phase, wherein the water phase comprises a carbon black pigment having a pH of less than 8 dispersed therein by a water-soluble resin, and wherein the water phase also comprises a pH-adjusting agent to achieve a pH value for the water phase of 8 or greater. The ink maintains stable rheology on ageing, and provides a stable and consistent ink detection signal even after periods of non-use.