Original scientific paper

https://doi.org/10.31803/tg-20191004140247

Near-infrared spectroscopy and hidden graphics applied in printing security documents in the offset technique

Vilko Žiljak* orcid.org/0000-0002-1190-5003 ; Faculty of Graphic Arts, University of Zagreb, Getaldićeva 2, 10000 Zagreb, Croatia
Jana Žiljak Gršić orcid.org/0000-0002-1190-5003 ; Zagreb University of Applied Sciences, Vrbik 8, 10000 Zagreb, Croatia
Denis Jurečić ; Faculty of Graphic Arts, University of Zagreb, Getaldićeva 2, 10000 Zagreb, Croatia
Tonči Jeličić orcid.org/0000-0001-7129-0541 ; Hydrographic Institute of the Republic of Croatia, Zrinsko-Frankopanska 161, 21000 Split, Croatia

Abstract

The method of mixing pigments for the printing technology is expanded with the addition of dual states in security graphics. Near-infrared spectroscopy of colorants used in the offset technique has brought about the concept of targeted design by a selective use of colorants that are visible in the visible region of the electromagnetic spectrum. High-security documents have been observed in the NIR light based on twin colorants which are differentiated according to their NIR absorption in the range from 800 to 1000 nm. New procedures have been developed based on the innovative creation of documents with hidden information. Two graphics are combined with mutating screen elements. A mathematical definition of the new printing screen and an algorithm in PostScript are given. The designer plans and creates graphics, which originate from the twin colorants, by using the INFRAREDESIGN® method. The dual design was investigated using visual and infrared cameras for the forensic area. The components of colorants are determined by the spectroscopy of light absorption with filters in the visual and NIR spectrum.

Keywords

hidden graphics; near-infrared spectroscopy; offset printing; security screen; twin colorants

Hrčak ID:

229500

URI

https://hrcak.srce.hr/229500

Publication date:

11.12.2019.

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