PROBLEM TO BE SOLVED: To provide an ink containing a pigment as a coloring material, in particular, a self-dispersion type carbon black, and having excellent ink jet recording characteristics. SOLUTION: The carbon black contains at least a colorant containing a self-dispersible carbon black having at least one hydrophilic group bonded directly or via another atomic group to a surface of the carbon black, and an aqueous medium. An ink characterized by having a potassium ion content of 0.6% or more by mass relative to the ink.