Beam hardening in X-ray tomography is often corrected using an arbitrary polynomial whose coefficients are subjectively selected. A better approach is to model X-ray generation, transmission and detection and to use step wedge transmission measurements to fit the model parameters. This allows for extrapolation of linearization curves beyond the range of the step wedge and it allows this curve to be adjusted according to the specimen composition without changing
the composition of the step wedge. This paper presents the principles behind beam-hardening and the model used for correction. Initial tests of this method have shown very good results where a priori knowledge of the specimen composition is available.