Thermal printers and methods for operating a thermal printer that applies donor material from donor patches on a donor ribbon to a received medium, the donor material being organized into sets, each set including at least one colored donor material patch and a protective material donor patch. A non-visible light is applied to a location on the donor ribbon, and a portion of the non-visible light that is not absorbed by the donor ribbon is sensed. The sensed non-visible light determines whether the portion of the donor ribbon to which the non-visible light has been applied has unused protective donor material thereon.