Letterpress is the oldest relief printing technique. The relief printing plate and the printing types are elevated above the non-printing elements. In the printing machine, ink is applied to the printing elements and transferred directly onto the substrate – usually paper.
Relief printing is especially used when numbering security printed items, or in creating the perforation for making tearing out individual pages easier, etc. The numbering produced by relief printing has its typical edge in individual printed numbers acquired from the pressure exerted by the numbering type onto the paper. Unlike the numbering produced in digital print it is possible to use a wide range of security printing inks.
SPWS also uses the technique of indirect letterpress printing (the so-called letterset method) in printing of banknotes and other security printed items in the Simultan printing machine, which allows simultaneous double-sided printing with extraordinary accuracy of concurrent printing.