Abstract: A ribbon, adapted for use on an impact printer, is provided wherein the ribbon is impregnated with a first substantially colorless substance which acts as a color-former when reacted with a second substantially colorless substance acting as a color-developer, present on a portion of a substrate. Upon the transfer of the color-former from the ribbon to the substrate by impact, a colored image will form on those areas of the substrate which are coated or impregnated with the color-developer. Images may thus be selectively transferred to an interior ply of a multi-ply business forms assembly by the conventional transfer methods without appearing on the exterior, impact receiving ply of such an assembly.