Chemically sensitive ink works instantly. An amber mark passes the test, while a dark brown or black mark means the bill is probably written. Works on all new design U.S. currency (bills series 1959 and later). Counterfeit Bill Detector Pen; Marking Color: Amber; Counterfeit Indicator : Black; Dark Brown Includes twelve counterfeit detector pens. 2. Product **and other products made in Japan are not applicable. 3. Packaging and instructions are in English.