Abstract: A coating composition is applied to a print stock substrate for preparing a thermally-active layer, the coating composition comprising: a developer comprising at least one or a combination of 6′-dipentylamino-3′-methyl-2′(phenylamino)-spiro [isobenzofuran-1(3H),9′-[9H]xanthen]-3-one (CAS No. 129473-78-5) and 6′-dibutylamino-3′-methyl-2′(phenylamino)-spiro [isobenzofuran-1(3H),9′-[9H]xanthen]-3-one (CAS No. 89331-94-2); a sensitizer comprising at least one or a combination of 1,1′-sulfonylbisbenzene (CAS No. 127-63-9) and dimethylterephthalate (CAS No. 120-61-6); and a coreactant (or developer) comprising at least one or a combination of bis(4-hydroxyphenyl)-4-methylpentane (CAS No. 6807-17-6) and 4-hydroxy-4′-isopropoxydiphenylsulfone (CAS No. 95235-30-6). Preferably, the print stock substrate will be coated with clay or the like to provide a smooth coating surface for the thermally-active layer.