PURPOSE: To obtain a printed matter rich in originality and surprisingness and preferable for use as a greeting card or the like, by forming latent images on a base by printing in at least two colorless or white inks each of which comprises an electron-donative dye precursor and an electron-acceptive compound for forming a color at the time of being heated.

CONSTITUTION: Printing on a base is conducted by using at least two colorless or white inks each of which comprises an electron-donative dye precursor and an electron-acceptive compound for forming a color at the time of being heated. For example, the electron-donative dye precursor is dispersed with a polyvinyl alcohol solution by a ball mill, whereas 2,2-bis (4-hydroxyphenyl)propane as the electron-donative compound is dispersed with a polyvinyl alcohol solution by a ball mill. Next, calcium carbonate, sodium hexametaphosphate and water are uniformly dispersed by a homogenizer. After the dispersed liquids are sequentially mixed with each other, hydroxyethyl cellulose is added to the mixture, then the resultant mixture is used for printing on a paper base after being controlled in viscosity. When the printed paper base is heated to, for example, 150°C, a clear four-color printed image is developed.