Energy dispersive X-ray spectroscopy can be used to identify alloy types quickly and, in many cases, to distinguish between alloy systems within a certain alloy type. Characteristic X-rays of major components in an alloy are produced through excitation by an isotopic source. Ratios of the X-ray intensities of a pair of elements are plotted vs. ratios of the theoretical weight fractions of these elements. This provides a unique data point which is a function of the composition of the particular alloy system. In some cases, characteristic X-rays of minor constituents are used for total identification.