Optical control of colour deviation due to ink showing through on the banknote reverse on multitoned watermarks

As the inhomogeneity of the paper structure in the areas of watermarks increases, the accuracy of the colour characteristics on the original print changes, as well as the uneven ink showing through on the back of the print, what causes unjustified withdrawal of suitable banknotes due to misjudgement of their condition as worn out. Therefore, to ensure the proper quality of automated sorting of banknotes, a methodology for predicting changes in the colour of the print return on special purpose paper should be developed taking into account its structural characteristics and a methodology for determining quantitative values of paper clearance characteristics with halftone watermarks.