INK COMPOSITION

An ink composition includes colorant, co-solvent system, acid (e.g., oleic, linoleic, undecanoic, dodecanoic, and/or tridecanoic acids), lithium, polymer as binder, and water. The co-solvent system is selected from i) from ˜9 to ˜25 wt % of sulfolane with no other co-solvent, ii) hydroxylated co-solvent, from ˜4 to ˜16 wt % of sulfolane, and at least 8 wt % of another non-hy-droxylated co-solvent; iii) hydroxylated co-solvent, from ˜7 to ˜16 wt % of sulfolane, and at least 3 wt % of the other non-hydroxylated co-solvent; and iv) a hydroxylated co-solvent and from ˜9 wt % to ˜16 wt % of sulfolane. When i) or ii) or iv) is used, at least 0.15 wt % acid and at least 200 ppm lithium are included; or when iii) is used, at least 0.25 wt % acid and at least 100 ppm lithium are included; or when iii) is used, at least 0.15 wt % acid and at least 150 ppm lithium are included.