An authenticable and machine readable coating for pills, tablets and other ingestible materials is provided. The disclosure also relates to methods of authenticating the same. The coatings are formed from a lattice of particles stacked to cause selective diffraction such that each pill or tablet has an optical signature. The signature associated with each coating can be read and authenticated. In one embodiment, the particles are substantially spherical and self-organized. In one embodiment, generally recognized as safe (GRAS) materials are used to form the particles.
