The invention relates to a method for characterizing the nature of a material, comprising: providing at least one sample (100) of said material between a source of X rays (1) and a detector; using the X ray source for making N spectra of X radiation transmitted through said material, and each having a duration ?t; calculating the transmission function of said material on the basis of the energy or the detection channel; in each of at least 2 energy areas, calculating the integral of the transmission function in order to obtain at least a first transmission coefficient (a1) and a second transmission coefficient (a2).