the term u201c cure u201d should be read to cover all mechanisms of ink becoming solid such as drying cross linking uv curing etc as the process of spray powder coating is well known to practitioners in the field of printing it will not be further described herein the inventors have discovered that mixing an authentication material with the spray powder constitutes an unexpectedly good way of distributing the material for the following reasons a the same powder can be used with all inks and papers simplifying logistics b since the powder does not mix with the ink but sticks to the top layer the authentication material is not contaminated by the ink this greatly reduces the amount needed for reliable detection concentrations as low as one part per million can be detected c since the concentration of the authentication material is low it is difficult for counterfeiters to establish the composition of the authentication material via chemical analysis of the ink and paper ink and paper contain many impurities at much higher concentrations then the authentication material at the same time detection is easy with the proper detection unit as it looks only at the top surface of the ink where concentration of authentication material is higher d authentication materials.