Czére Andrea szerk.: A Szépművészeti Múzeum közleményei 102-103. (Budapest, 2005)

MARIANNA DÁGI - MÁRIA TÓTH: A Small Portrait Head of Augustus: Archeometrical Investigations

BOTTOM VIEW OF THE PORTRAIT AUGUSTUS. BUDAPEST. MUSEUM OF F Subordinate amounts of quartz (less than 1%) were also detected. This quartz might have come either from the original sulphur itself, or from the environment. Due to overlapping reflections, the presence of barite is uncertain. Amorphous (glassy) phases were not identified.

5 Although X-ray powder diffraction analysis is decisive on its own, further analyses were carried out in order to cross-check the surprising outcome. The same preparation used for the X-ray powder diffraction analysis was re-examined by electron microprobe. In order to define elemental composition, energy-dispersive analysis was carried out over the whole surface, looking for small domains of massive material and also isolated crystallites. The following result was obtained. The whole surface of the sample consists overwhelmingly of sulphur, with smaller amounts of barium, and traces of silicon, aluminium, magnesium, calcium and iron (S>>>Ba>>Si, AI, Mg, Ca, Fe) also identified. The small domains of massive material also consist predominantly of sulphur and the other minerals found during analysis of the whole surface, but with a much smaller amount of barium (S>>>Si, AI, Mg, Ca, Fe, Ba). Individual crystals are composed of barium and sulphur (Ba, S). The results of the electron microprobe tests coincide nicely with those of X-ray powder diffraction analysis. The sample consists predominantly of sulphur. Elemental analysis also verified the presence of barite (BaS0

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). This mineral is present not only as idiomorphic crystals in the inside of the head, but also as microcrystals in the massive material (fig. 19). This suggests the sedimentary origin of the material examined. The characteristic crystalline structure of the sulphur confirms that the raw material from which the object was made is of natural origin. The monoclinic modification of sulphur (a-S) crystallizes from melted material, whereas rhombic sulphur (ß-S) crystallizes from solutions.

6 This means that the portrait head of Augustus in the Collection of Classical Antiquities was neither cast from melted sulphur, nor carved from a melted, then resolidified block; but was sculpted from a so-called geode, or lump formed in a sedimentary deposit of natural sulphur. 13 HEAD OF 1NE ARTS