Ink, and ink-jet recording method and instrument using the same

A water-based ink composition comprising coloring material particles having a core-shell structure obtained by adsorbing a dye on surfaces of cores, which are water-insoluble inorganic fine particles having a particle size on the order of about 0.1 .mu.m and having an isoelectric point of 7 or lower, or inorganic colloidal substances, and an aqueous solution of a water-soluble polymer and a thread-forming polymer, in which solution said coloring material particles are dispersed, wherein the polymer chains of the water-soluble polymer in the composition undergo dissociation or association in response to a temperature change ranging from 20.degree. to 50.degree. C. or pH change ranging from 7 to 10,

• wherein the water-soluble polymer is present in an amount of 0.01 to 10.0 percent by weight of the ink, and is selected from a mixture of polymethacrylic acid and polyethylene glycol, a mixture of polymethacrylic acid and polyethylene glycol-polypropylene glycol copolymer, a mixture of polyacrylic acid and a poly(N-alkyl-substituted acrylamide), a polyethylene oxide-polypropylene oxide-polyethylene oxide block copolymer, and a composite thereof;
• and
• wherein the thread-forming polymer is selected from polyethylene oxide, a starch thickener, a cellulose thickener, a seaweed thickener, a gum thickener, and a synthetic thickener.