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Of all the materials examined, terracotta is the one for which the CT scan yields the most information on manufacturing techniques.
Since clay is initially soft, it keeps a trace of everything it has been in contact with before firing, whether it is the stand on which it was modeled, the potter’s fingers or tools. Because of its relatively adhesive nature, fresh clay sometimes incorporates dust or residue of varying density. These marks enable the radiologist to trace the sequence of steps in the creation of the work and to pinpoint any inconsistencies. A plausible explanation must be found for these inconsistencies, in a field where fakes are legion.
A CT scan of a terracotta object also permits a study of the granulometry of the metal flecks it contains as well as of its overall density. Generally speaking, both the granulometry and global density of the clay are constant in the same sculpture, as the artist theoretically shapes his work from the same stock of clay. Moreover, the CT scan gives information about the metal or organic supporting structures used by the artist during modeling, whether or not they survived the firing process. Lastly, it reveals the way stamped pieces were assembled, the quality of the glaze, changes made before firing and traces of early paintwork.
On the other hand, when previously fired terracotta material – excavated bricks, for example – is cut, carved, hollowed out, assembled, scraped, sanded, painted, etc., to produce a sculpture which looks like an original piece, a whole range of other signs are revealed by the CT scanner which frequently prove its recent assembly.