Portable equipment for energy dispersive X-ray fluorescence analysis of Giotto’s frescoes in the Chapel of the Scrovegni

doi:10.1016/S0168-583X(03)01758-0

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms

Volume 213, January 2004, Pages 703-706

https://doi.org/10.1016/S0168-583X(03)01758-0 Get rights and content

Abstract

Photon induced energy dispersive X-ray fluorescence (EDXRF) analysis is a valuable technique for the study of works of art, because it is nondestructive, multielemental, simple and relatively inexpensive. For this reason EDXRF is a very popular analytical technique in archaeometry.

Portability of EDXRF equipments is extremely useful and almost mandatory in many cases, such as analysis of frescoes, of large paintings, bronzes, brasses and gold alloys, and so on, especially when located in museums.

EDXRF analysis generally involves an area of a few mm², and a thickness between μm and fractions of mm and, therefore, the analysis is superficial and dependent on the surface conditions.

The frescoes by Giotto in the “Chapel of the Scrovegni” in Padua were systematically analysed in the period July 2001–March 2002 in more than 300 points, before, during and after restoration, in order to detect the possible presence of superficial sulphur and to test various sulphur cleaning procedures. Further all pigments were systematically analysed in order to determine their composition. Golden haloes were also analysed and different pigment layers were detected under the gold leaf; from the EDXRF analysis the attribution of chemical elements to the proper layer was possible.

Introduction

The famous frescoes by Giotto in the “Chapel of the Scrovegni” in Padua were systematically analysed during July and September 2001, and March 2002 in more than 300 points, before, during and after restoration.

Begun in 1303 and consecrated on March 25, 1305, the chapel is dedicated to Our Lady of the Annunciation and was commissioned by Enrico Scrovegni in suffrage for the soul of his father, Reginaldo, accused of usury. It was Enrico Scrovegni who commissioned Giotto to execute the frescoes in the interior of the chapel, where the master attained the height of his artistry, for this cycle of paintings which was defined a point of no return in the entire history of western painting.

One of the most important questions during restoration was to detect the superficial presence of sulphur compounds and to remove them. Sulphur is due to the combustion of coke, petroleum and gasoline and is an index of pollution. It is often present, in various chemical forms, mainly as CaSO₄ on the surface of frescoes and monuments, producing black colouring. It should be removed to avoid growing damages.

Almost all pigments of Giotto’s fresco were systematically analysed in order to determine their composition. Golden haloes were particularly studied.

Three different portable EDXRF equipment were employed, according to the elements to be analysed. They are all composed of small size, low power X-ray tubes, thermoelectrically cooled Si-PIN detectors and portable multichannel analysers. Typical measuring time was of 100–200 s.

Section snippets

Theoretical background

When radiation from a X-ray tube penetrates the pigments of a fresco, it is absorbed along its path. A fraction of the energy of the absorbed photons is converted into fluorescent photons of the various elements, and some of them reach the surface of the fresco [1].

In the case of Giotto’s frescoes in the chapel of the Scrovegni the complexity of the X-ray spectra – for example in the golden haloes – puts in evidence the presence of various pigment layers. These are very thin, because also an

Experimental set-up

Three different portable equipment were employed; of them two for the analysis of sulphur and the third for the analysis of the pigments, including gold.

For the analysis of S a Ca-anode Hamamatsu X-ray tube was employed, working at about 4 kV, 60 μA, coupled to a thin Be-window AMPTEK Si-PIN detector (Fig. 1). The Ca-anode X-ray tube emits fluorescent radiation of 3.6 keV which is not able to directly excite Ca which is highly present in the fresco. Alternatively a Pd-anode X-ray tube was used,

Results and discussion

Sulphur was detected everywhere in the fresco, and a typical low-energy X-ray spectrum, obtained with the Ca-anode X-ray tube working at 4.5–5 kV, is shown in Fig. 1. The penetration of these low-energy X-rays is limited to a few microns. Besides S, X-rays of the elements Ar, K and Ca are visible in the X-ray spectra, originating from the surface of the fresco or from the air surrounding the detector (Ar).

The sulphur-cleaning process, of great importance for the restoration of the fresco, was

References (3)

M. Mantler et al.
X-ray Spectrom.
(2000)
A. Neelmeijer et al.
X-ray Spectrom.
(2000)

There are more references available in the full text version of this article.

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