The invention relates to a method for x-ray examination of an object where two categories of materials are taken into consideration, comprising: the use of broad spectrum x-rays; measurements of the x-rays by bands of the spectrum; expressions ({circumflex over (M)}) of thicknesses or masses of the two categories of materials passed through by the x-rays, the expressions ({circumflex over (M)}) being functions of at least two of the measurements (mes.sub.k) and coefficients (A); and applying a selection criterion from among the expressions ({circumflex over (M)}) to deduce from this an expression (final {circumflex over (M)}) considered true; characterized in that the selection criterion comprises a combination (f) of the expressions with weighting factors (a), and a calculation of the weighting factors such that the combination has minimal variation according to variations of the measurements.