An energy sensitive imaging system like Medipixl has proved to be promising in distinguishing different materials in an X-ray image of an object. We propose a general method utilising X-ray energy information for materialrecognition. For objects where the thickness of the materials is unknown, a convenient material parameter to identify is K = α1/α2, which is the ratio of the logarithms of the measured transmissions In(t1)/In(t2). If a database of the parameter K for different materials and energies is created, this method can be used for material recognition independent of the thickness of the materials. Series of images of an object consisting of aluminium and silicon were taken with different energy thresholds. The X-ray absorption for silicon and aluminium is very similar for the range 40-60 keV and only differs for lower energies. The results show that it is possible to distinguish between aluminium and silicon on images achieved by Medipixl using a standard dental source. By decreasing the spatial resolution a better contrast between the materials was achieved. The resolution of contrasts shown by the histograms was close to the limit of the system due to the statistical noise of the signal.