A security ink for printing a machine readable security feature, said security ink comprising one or more IR absorbing materials selected from the group consisting of crystal water-free iron orthophosphates of the general formula Fe 3 (PO 4) 2 and having a graftonite crystal structure, crystal water-free iron metal orthophosphates, crystal water-free iron metal phosphonates, crystal water-free iron metal pyrophosphates, crystal water-free iron metal metaphosphates of the general formula Fe a Met b (PO c) d, where a is a number from 1 to 5, b is a number from >0 to 5, c is a number from 2.5 to 5, d is a number from 0.5 to 3 and Met represents one or more metals selected from the group consisting of Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, the transition metals (d block), in particular Sc, Y, La, Ti, Zr, Hf, Nb, Ta, Cr, Mo, W, Mn, Cu, Zn, Co, Ni, Ag, Au, the metals and semimetals of the third, fourth and fifth main groups, in particular B, Al, Ga, In, Si, Sn, Sb, Bi and the lanthanoids, and mixtures thereof wherein said security ink is an oxidative drying security ink comprising from 0.01 wt-% to 10 wt-% of one or more driers, the weight percents being based on the total weight of the oxidative drying security ink, or a UV-Vis curable security ink comprising from 0.1 wt-% to 20 wt-% of one or more photoinitiators, the weight percents being based on the total weight of the UV-Vis curable security ink, or a thermal drying security ink comprising from 10 wt-% to 90 wt-% of one or more solvents selected from the group consisting of organic solvents, water and mixtures thereof, the weight percents being based on the total weight of the thermal drying security ink, or a combination thereof. crystal water-free iron orthophosphates of the general formula Fe 3 (PO 4) 2 and having a graftonite crystal structure, crystal water-free iron metal orthophosphates, crystal water-free iron metal phosphonates, crystal water-free iron metal pyrophosphates, crystal water-free iron metal metaphosphates of the general formula Fe a Met b (PO c) d, where a is a number from 1 to 5, b is a number from >0 to 5, c is a number from 2.5 to 5, d is a number from 0.5 to 3 and Met represents one or more metals selected from the group consisting of Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, the transition metals (d block), in particular Sc, Y, La, Ti, Zr, Hf, Nb, Ta, Cr, Mo, W, Mn, Cu, Zn, Co, Ni, Ag, Au, the metals and semimetals of the third, fourth and fifth main groups, in particular B, Al, Ga, In, Si, Sn, Sb, Bi and the lanthanoids, and mixtures thereof wherein said security ink is an oxidative drying security ink comprising from 0.01 wt-% to 10 wt-% of one or more driers, the weight percents being based on the total weight of the oxidative drying security ink, or a UV-Vis curable security ink comprising from 0.1 wt-% to 20 wt-% of one or more photoinitiators, the weight percents being based on the total weight of the UV-Vis curable security ink, or a thermal drying security ink comprising from 10 wt-% to 90 wt-% of one or more solvents selected from the group consisting of organic solvents, water and mixtures thereof, the weight percents being based on the total weight of the thermal drying security ink, or a combination thereof. wherein said security ink is an oxidative drying security ink comprising from 0.01 wt-% to 10 wt-% of one or more driers, the weight percents being based on the total weight of the oxidative drying security ink, or a UV-Vis curable security ink comprising from 0.1 wt-% to 20 wt-% of one or more photoinitiators, the weight percents being based on the total weight of the UV-Vis curable security ink, or a thermal drying security ink comprising from 10 wt-% to 90 wt-% of one or more solvents selected from the group consisting of organic solvents, water and mixtures thereof, the weight percents being based on the total weight of the thermal drying security ink, or a combination thereof.