1. A method for introducing a print characteristic in a visible image printed on paper, comprising printing a part of the image with an ink having first and second components, the first component being less fast than the second component in response to an applied activator, and the first component being a fluorescent component having its fluorescence substantially masked in the presence of the second component in the absence of the applied activator, and applying the activator to stimulate a bleed of the first component beyond the area of said part to create a unmasked area of the fluorescent component at the area of the bleed.