e of adjusting polymer characteristics. [0055] The black ink according to the invention may include a polymer such as polyvinyl alcohol, polyvinyl pyrrolidone, polyacrylamide, poly N-vinylacetamide and the like. [0056] When the polymer is a water-soluble polymer, a weight-average molecular weight of the polymer is preferably in the range of 1,000 to 30,000, and more preferably in the range of 3,00