Abstract: A water-based ink includes a pigment, an amino acid having an alkylene group with three or more carbon atoms and having amino groups on a side chain thereof, a surfactant and/or a penetrating agent, and water. The surfactant includes an acetylene based surfactant. The penetrating agent includes an alkylene diol, a glycol ether compound, or both. An amount of the amino acid in the water-based ink relative to a total mass of the water-based ink is from 0.05 to 1 mass %. The amino acid is preferably arginine, lysine, or both. The water-based ink preferably further includes two or more wetting agents.

Abstract: A water-based ink includes a pigment, an alkali metal hydrogencarbonate, and water. An amount of the pigment and an amount of the alkali metal hydrogencarbonate satisfy Condition (1): Condition (1): 7.5?A/B. A is a solid amount of the pigment by mass in the water-based ink relative to a total mass of the water-based ink, and B is the amount of the alkali metal hydrogencarbonate by mass in the water-based ink relative to the total mass of the water-based ink. A pH of the water-based ink is preferably less than 9.2. A pH of the water-based ink after a storage of the water-based ink at 60° C. for 1 week is preferably 7.8 or more. A change in pH between before the storage and after the storage is preferably 10% or less.

Abstract: A water-based ink includes: a dye; water; an acidic preservative; and at least one of a surfactant and a penetrant. The acidic preservative preferably includes at least one selected from the group consisting of a polyvalent unsaturated fatty acid, a polyvalent unsaturated fatty acid salt, dehydroacetic acid, and a dehydroacetate. A content of the acidic preservative in the water-based ink is preferably 0.3% by mass to 6.0% by mass relative to a total mass of the water-based ink. The surfactant preferably includes an acetylene-based surfactant. The penetrant preferably includes at least one selected from the group consisting of an alkylene diol and a glycol ether compound.

Abstract: A water-based ink for inkjet recording, includes: a pigment; water; and an acidic preservative. The pigment is preferably a self-dispersing pigment. The acidic preservative preferably includes at least one selected from the group consisting of a polyvalent unsaturated fatty acid, a polyvalent unsaturated fatty acid salt, dehydroacetic acid, and a dehydroacetate. A content of the acidic preservative in the water-based ink is preferably 0.5% by mass to 5.0% by mass relative to a total mass of the water-based ink. The water-based ink preferably further includes a surfactant. The water-based ink preferably further includes a penetrant which includes at least one selected from the group consisting of 1,2-hexanediol, 3-methyl-1,5-pentanediol, and triethylene glycol-n-butyl ether (BTG).