The present invention relates to the field of security inks suitable for printing machine readable security features on substrate, security documents or articles as well as machine readable security feature made from said security inks, and security documents comprising a machine readable security feature made from said security inks. In particular, the invention provides security inks comprising one or more IR absorbing materials selected from the group consisting of crystal water-free iron(II) orthophosphates of the general formula Fe3(PO4)2 and having a graftonite crystal structure, crystal water-free iron(II) metal orthophosphates, crystal water-free iron(II) metal phosphonates, crystal water-free iron(II) metal pyrophosphates, crystal water-free iron(II) metal metaphosphates of the general formula FeaMetb(POc)d, wherein said security ink is an oxidative drying security ink, a UV-Vis curable security ink, a UV-Vis curable security ink or a combination thereof.