X-ray fluorescence analysis of yellow pigments in altarpieces by Valencian artists of the XV and XVI centuries

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Abstract

XRF analysis has allowed a quick and precise detection and identification of the inorganic elements that compose the yellow pigments in altarpieces of the XV and XVI centuries painted by the Valencian artists Miguel Alcañiz, Vicente Macip, Juan de Juanes, Hernando Yáñez de la Almedina and Hernando Llanos. The analyses have been carried out with an XRF portable system that consists of a tube of X-rays and detectors of Si(Li) and cadmium zinc telluride. This system has enabled a non-aggressive and non-destructive analysis of many pieces at the Museo de Bellas Artes of Valencia (Spain). Among the yellow pigments we have identified a pigment composed by lead and tin oxides named lead–tin yellow (Pb2SnO4), frequently used in European paintings from the XIV century until the first half of the XVIII century. This fact demonstrates the influence of elements and pictorial techniques from Europe to the region of Valencia.

Introduction

The integrity of the works of art is the main premise that should guide the professional work of art restorers and conservators, and it should also be a norm for the techniques used to characterize them. There are non-destructive and non-aggressive analytical techniques like the X-ray fluorescence analysis (XRF) that, without attacking or destroying the work provides valuable qualitative information about their elementary chemical components [1]. In addition, the configuration of a portable and easy operation equipment which can be transported from the laboratory to the museum, avoiding any transport of the museum objects in the other direction, has obvious advantages for the integrity of these objects. For this purpose portable XRF systems have been widely used 2, 3, 4.

This paper has two objectives. The first is to present a simple, inexpensive and portable XRF system, developed by the Archaeometry Unit of the Instituto de Ciencia de los Materiales de la Universidad de Valencia (ICMUV), that consists of a small size X-ray tube (0–50 kV, 1 mA), a high resolution Si(Li) cryogenic detector, a Peltier cooled cadmium zinc telluride detector, and modular electronic components to process the detector signals. With these elements we have carried out non-aggressive and non-destructive “in situ” analysis of the paintings at the Museo de Bellas Artes of Valencia.

Our second objective is the analysis, with this XRF system, of the yellow pigments used by the most important Valencian painters of the 15th and 16th centuries, Miguel de Alcañiz, Vicente Macip, Juan de Juanes and the Castilian painters who settled in Valencia, Hernando Yáñez and Hernando Llanos. An extensive study with physical and chemical analysis carried out by Kühn [5]shows that the lead–tin yellow pigment, in disuse from 1750, was frequently used by Italian, Flemish and German artists from 1300. This work reports that the lead–tin yellow pigment was also used by painters established in Valencia (Eastern coast of Spain) during this period. We also present the element identification of some degraded ochre pigments used by the above cited authors.

Section snippets

Material and methods

Pigment identification was achieved with an XRF system integrated by a small size X-ray tube (Oxford Instruments, model XTF5010) that produces a beam of X-rays coming from an anode of rhodium. The voltage and current intensity of the X-ray source are continuously variable from 0 to their maximum values, 50 kV and 1 mA. The energy of the produced X-rays are large enough to excite the characteristic K and L X-ray lines of the elements present in the samples with atomic number greater than that of

Results and discussion

A total of 19 altarpieces were analyzed with the equipment previously described. The analyses of the XRF spectra enables identification of the energy and the intensity of the peaks. The selection of the voltage of the X-ray tube is a commitment between the penetration and the electronic transitions that we want to induce on the pigment. We have used voltages of 8 and 15 kV to excite low energy electronic transitions and to analyze the superficial layers, voltages of 25, and 35 kV have been used

Conclusions

The Archaeometry Unit of the ICMUV has configured a portable XRF equipment that enabled us to carry out qualitative and non-destructive “in situ” analyses to study medieval paintings from the Museo de Bellas Artes of Valencia. The XRF system is integrated by a X-ray tube (0–50 kV, 1 mA), a high resolution cryogenic Si(Li) detector and a small size Peltier cooled CdZnTe.

With this XRF system we have analyzed altarpieces by M. Alcañiz, V. Macip, H. Llanos, H. Yáñez and J. de Juanes, painters that

Acknowledgements

The authors have been supported in this work by a Conselleria de Educació i Ciència project GV-3185/95. The authors are grateful to the Servicio de Restauración y Conservación de Bienes Museı́sticos and the Departamento de Restauración of the Museo de Bellas Artes of Valencia.

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