US Patent 7238396 Methods for vitrescent marking

Methods for vitrescent marking of substrates, likes bricks, are described that include placing the substrate to be marked and at least one marking material in reactive contact with each other and vitrifying the substrate and the marking material to form a marking below the outer surface of the substrate. The vitrification may be accomplished by irradiating the marking material and the substrate with a radiant energy beam that has a wavelength and an energy level sufficient to vitrify the marking material and the substrate for form a vitrescent marking that is below the outer surface of the substrate.