“The printing process in question is a simple but, as usual with Keats, pretty clever idea. The cover is printed in a double layer of standard black ink, with an incrementally screened overlay masking the nine words. Exposed over time to ultraviolet light, the words will be appear at different rates, supposedly one per century. “The precise quantity of ink covering each word is different, so that the words will appear one at a time,” Keats said. “Provided that your copy of Opium is kept out in the open, and regularly exposed to sunlight over 1,000 years to be read progressively by the next dozen or so generations. Or very, very slowly if you happen to be Ray Kurzweil.” - × × ×