Abstract: A heat-sensitive coating composition, and heat-sensitive material for thermal imaging containing the heat sensitive composition. The composition comprises a color-forming amount of a finely divided, solid, colorless noble metal salt of an organic acid; a color-developing amount of an organic reducing agent which at thermal copy and printing temperatures is capable of a color-forming reaction with the noble metal salt; an image toning agent; and a carrier composition in which the noble metal salt, organic reducing agent, and toning agent are distributed. The carrier composition requires no organic solvents and comprises one or more substantially water-soluble polymeric carrier materials and a solubility-enhancing amount of a dispersing agent. A protective, clarifying, radiation-cured overcoat is provided. Methods of forming the heat-sensitive composition and the overcoat are also disclosed.