vai al contenuto della pagina vai al menu di navigazione
 

X-ray Computed Tomography of an ancient big globe

X-ray Computed Tomography of the ancient globe built by Egnazio Danti in 1567 (June 2004)
X-ray Computed Tomography of an ancient big globe

University of Bologna Team Leader: Prof. Franco Casali

University of Bologna Research Group: Franco Casali, Morigi Maria Pia, Matteo Bettuzzi, R. Brancaccio.

Partner/Collaborations: University of Bologna, Opificio delle Pietre Dure (Florence), Municipality of Florence.

Context and objectives

Born in the early Seventies for medical applications, X-ray Computed Tomography (CT) is currently playing an increasingly important role in the field of Cultural Heritage diagnostics. It represents a powerful non-destructive investigation technique, capable of displaying in a three-dimensional way the volume and the internal structure of the investigated objects, also thanks to modern 3D rendering techniques.

The objectives of a tomographic survey of an artefact are to obtain information on the construction technique, the structure and the conservation status, both for knowledge and for setting-up a proper restoration.

Methodologies and equipment

The first applications of Computed Tomography to Cultural Heritage diagnostics have been done by means of medical CT scanners, usually with courtesy and permission of an hospital. However, medical scanners give good results only in case of analysis of samples with size and density similar to those of the human body, a condition that is rarely met in the field of Cultural Heritage, characterized by a considerable variability in the shapes, sizes and the constituent materials.

Sometimes the dimensions of the works of art are so huge that it impossible to inspect them by a standard equipment. Moreover, the big objects often cannot be moved from the places where they are located.

These reasons are behind the growing interest for versatile inspection systems, capable to perform the tomographic analysis on site. In the last ten years, our research group has developed several transportable CT systems and one of them has been expressly conceived for the investigation of large objects.

Results

Several years ago our research group carried out a CT investigation on the big ancient globe (220 cm in diameter) created by the Dominican monk Egnazio Danti in 1567 and located at Palazzo Vecchio in Florence (Fig. 1 - Gallery).

The CT system was set-up inside the "Map Room" of Palazzo Vecchio and the acquisition of the radiographic images (more than 32000) was performed during the evening hours and the night when the tourists were not present inside the museum. Thanks to the 3D tomographic reconstruction, it was possible to visualize the entire inner structure (Fig. 2 and Fig. 3 - Gallery), made of iron, and to estimate its total weight (about 350 kg).

The 3D rendering allows also a manipulation of the reconstructed volume; in this way it is possible to enhance significant details, or isolate regions of interest (Fig. 4 - Gallery), in order to perform a more precise investigation of the nature and the condition of a specific component.