Academic journal article Heritage Science

Thermographic Inspection of Cracks in the Mixed Materials Statue: Ratto Delle Sabine

Academic journal article Heritage Science

Thermographic Inspection of Cracks in the Mixed Materials Statue: Ratto Delle Sabine

Article excerpt

Authors: Maria C Di Tuccio (corresponding author) (equal contributor) [1,2]; Nicola Ludwig (equal contributor) [1]; Marco Gargano (equal contributor) [1]; Adriana Bernardi (equal contributor) [2]

Introduction

In order to preserve the ?Ratto delle Sabine? model the Ministero dei Beni e delle Attivit? Culturali e del Turismo commissioned the restoration of this work of art. Before intervening, numerous analyses were performed by different scientists to study this particular statue. One of them foresaw the use of infrared thermography.

During the last decades, the Infrared Thermography (IRT) has evolved into a powerful non-destructive tool to study the state of Cultural Heritage artefacts and monuments. IRT is applied following two different approaches: ?passive thermography? when only the naturally occurring temperature variations in the object need to be analysed and ?active thermography?, when an external stimulus is needed to produce relevant thermal contrasts. To highlight the presence of anomalies or the different thermal behaviour of the materials (evidencing for example cracks or detachments), both techniques require differences in temperatures of at least a few degrees.

Infrared thermography (IRT) has been widely applied to study buildings [1],[2], monuments [3],[4] and frescoes [3],[5]-[9] and to analyze other artefacts such as paintings (wooden paintings and canvas) [9]-[14] or sculptures [15]-[18].

The ?Ratto delle Sabine? (Figure?1) is one of the oldest preserved models at a 1:1 scale, constructed by Giambologna between 1579 and 1580. It was used as model for the realization of the final marble statue and, therefore, it represents an interesting opportunity to investigate the sculptural capacities of Giambologna.

Figure 1: The model statue of The ?Ratto delle Sabine? of Giambologna. [see PDF for image]

The radiographic analysis[sup.a] [19] and the visual inspection of the surface during restoration[sup.b] [20] showed that the model is composed mainly by raw clay in the outer part and by several different materials in the inner part. In particular the radiographic inspection [19] showed the presence of a core composed of various wooden elements differing in type and dimensions, in most cases joined together by nails in metal. In other parts of the ?Ratto delle Sabine? model the bonds seem to be made by means of joints and/or bandages. In the construction of some parts of the artefact (stomach and head of the Romano warrior) materials have been used which are lighter (e.g. cloth) than raw clay. This was probably done in order to make the work lighter and less subject to withdrawal during the solidification of the entire statue [20].

The different physical properties (in particular the specific weight) of the materials, related to the use in the model caused the formation of several cracks of the raw clay, a material which delaminates easily thereby increasing the rupture risk [20].

In exposition places (ex. museums, galleries, etc.), where the environmental conditions need to be controlled within small ranges to avoid thermal stress to the artworks [21], the use of passive thermography is often unsuccessful because the work of arts do not show relevant differences in the surface temperature distribution. In these cases an active approach of the thermography is required to make relevant thermal contrasts of the defects like cracks visible.

In order to analyse the eventual interconnection between the cracks previously identified by other investigations (radiography and visual inspection) of the ?Ratto delle Sabine? model, a more localized methodology of active infrared thermography was set up. This would lead to the understanding of which specific parts of the model are more at risk of further damage and prevent any potential falling down of parts of the statue due to gravity.

In this case the usual heating (halogen lamps, thermo-convectors, etc. …

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