1. A method for operating a thermal printer adapted to print an image by heating donor material from one of sequence of sets of donor material patches on a donor ribbon and transferring the heat donor material to a donor ribbon, the method comprising the steps of: receiving image data for a first image to be printed; printing the first image exhausting only a fraction of a full donor patch set to leave a fractional donor patch set having sufficient donor material for the printing of a second image; and preventing the printing of a second image using the fractional donor patch set when it is determined that the printing of the first image has heated a minimum area of one of the donor patches of the donor ribbon above a threshold level.