scales may be readable to the human eye without microscopy, there is no differentiation between microprinting at these different scales. The first US postage stamp to incorporate microprinting was the American Wildflower Series introduced by The United States Postal Service in 1992. It was also the first commemorative stamp wholly produced by offset lithography. The USPS has since issued other stamps with more complex microprinting incorporated along with dates, words, and abbreviations such as USPS and even entire stamp designs composed of microprint letters. There was passing interest in microprinting as a solution to book storage in libraries in the 1940s. Librarian Fremont Rider championed microprinting over micro-film for its reduced cost. He also suggested that entire books could be printed on the backs of library catalog cards, which are generally blank, replacing the storage of full-sized books on library shelves. Production Microprint of the smallest scale is only producible by hand using engraved offset printing plates or some other method of Intaglio (printmaking). Digital microtext printers utilize specially designed fonts and ink for the purpose. The ink used is most commonly MICR (Magnetic Ink Character Recognition) toner particles but may also be polyester based toners and styrene acrylate polymer based toners. The ink is not limited to grayscale only, but may also use color toners or even more specialized toners containing dyes sensitive to ultraviolet or infrared radiation and producing fluorescence when exposed to those radiations. Microtext and microfonts Microprint of the scale capable by other printing methods cannot be produced by a digital printer regardless of the resolution of the device. Some digital fonts are designed specifically for the purpose of microprinting. These pseudo-microprint fonts are referred to as microtext. Xerox was acclaimed for developing a microtext font they claimed could produce characters 1/100 of an inch tall; 1/100 of an inch is equivalent to 0.72 points. In April 2015, Videojet Technologies released their 1650 High Resolution (HR) and 1620 HR Continuous Inkjet (CIJ) printers, said to be capable of printing sub-pixel size characters as small as 0.6 mm in height (equivalent to 1.70079 points). The printers use a 40-micron nozzle that outputs more than 100,000 drops per second of ink. While these printers make microprinting faster and easier to produce digitally, they still have not reached the true sub-pixel size of less than 1 point. The smallest scale microtext a laser printer can produce is 0.5 pt.