Abstract: A method of detecting counterfeit paper currency includes applying a test solution having an initial color to an area of a paper currency to be tested. After waiting for a predetermined time period, the color of the test area is compared with a predetermined standard to determine if a reaction has taken place, whereby on the application of the test solution to a counterfeit paper currency the net result will be a color change from its initial color to a black coloration and for a genuine paper currency there will be no immediate change in its initial color.