The evaluation of non-medical subjects with computed tomography (CT) is widespread and has been applied to the study of fossils. This is particularly useful when fossils are encased in host rock, the removal of which would prevent a more detailed analysis of the post-death history of the specimen. CT images can be segmented and rendered to give 3D visualisation. However, CT artefact can seriously reduce the quality of such images. The artefact of most concern occurs when high attenuation materials are found in lower attenuation material, but particularly when materials have irregular shape. The artefact reduction method used involved encasing the specimen, to form a cylindrical shape using gelatine based phantom material of similar attenuation. The calculated effective photon energy of the CT scanner was used, with the 'mixture rule', to iteratively determine the composition of the phantom material. High Z fillers were used to get the required attenuation associated with rocks. Artefact reduction was demonstrated by this method.