Patent ID: 7291213

Claim:
An ink composition comprising: a coloring agent having an oxidation potential of more electropositive than 1.0V (vs SCE) and being a dye represented by formula (2): wherein X 11 , X 12 , X 13 and X 14 each independently represents —SO-Z, —SO 2 -Z, —SO 2 NR 11 R 12 , a sulfo group, —CONR 11 R 12 or —CO 2 R 11 ; Z's each independently represent an alkyl group, an alkenyl group, an aralkyl group, an aryl group or a heterocyclic group, which may be further substituted by a substituent; R 11 and R 12 each independently represents a hydrogen atom, an alkyl group, an alkenyl group, an aralkyl group, an aryl group or a heterocyclic group, which may be further substituted by a substituent; Y 11 , Y 12 , Y 13 , Y 14 , Y 15 , Y 16 , Y 17 and Y 18 each independently represents a hydrogen atom or a monovalent substituent; a 11 to a 14 respectively stand for the numbers of substituents in X 11 to X 14 and each independently represents an integer of 1 or 2; and M represents a hydrogen atom, or a metal atom or an oxide, a hydroxide or a halide of the metal atom; a water; a guanidine compound selected from one of the following compounds: and a surfactant.