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A research group from UB identifies a signature in an artwork attributed to Goya with THz radiation

Image of the artwork <i>Sacrifice to Vesta</i> in the visible.

Image of the artwork Sacrifice to Vesta in the visible.

Image of the artwork with 50% visible and 50% THz.

Image of the artwork with 50% visible and 50% THz.

100% THz image.

100% THz image.



Researchers from the University of Barcelona have studied an artwork attributed to Goya by means of Terahertz (THz) time-domain system, a non-destructive testing technique applied to the artwork. The study, published on the journal Optics Express, the fourth one ranked by impact factor in the field of optics, identifies a signature at the bottom right corner of the work that remain hidden to other techniques previously used.

According to Javier Tejada, professor of Fundamental Physics at the UB,: “it is the first time that THz are used to ‘see’ a signature; there is not any precedent in scientific literature”. The paper demonstrates the potential of THz imaging. THz radiation covers the part of electromagnetic spectrum between the microwave and far infrared bands. It constitutes a complementary technique along with X-ray and infrared imaging for the verification and authentication of artwork pieces through the detection of features that remain hidden to optical inspection.

The doctorate students Cristina Seco, first author of the paper, Víctor López and Gianluca Arauz, supported by Albert Redó, from the company Z-Omega (USA), participated in the research, led by Javier Tejada.

A new technique to ‘see’ artworks

The inspected artwork, entitled Sacrifice to Vesta, is a documented artwork that belongs to a private collection owned by the art patron Félix Palacios (Zaragoza) and was painted by Goya during his stay in Italy in 1771. The painting shows a priest who is performing the rite of the sacred fire to Vesta, the Goddess of the Hearth and Fire.

THz images are formed from the binding of 1 mm2 images obtained from the reflection of this radiation. THz waves reach several layers of paint and provide a three-dimensional image of the artwork. Moreover, THz radiation is absorbed and reflected in a different way depending on the type of pigment and material. This fact provides extra spectroscopic information about the materials used in the artwork.

In relation to the alleged signature, assuming that it was written using a pencil (basically carbon) and that the painting was covered by a top layer of finishing varnish that turned dark over time, it is expected that X-ray images cannot detect the signature because the surrounding canvas and the paint are very similar. In this case, THz waves are more sensitive to molecular composition and to the different reflectivity of carbon and the surrounding canvas, which provides the mechanism for the detection of the signature.

“Results offer new possible technological niches in which this technique may solve problems”, remarks Tejada. The group from the UB is now working on topics related to pharmacology, biomedicine or car industry. “In some years, this technology will come right into science to tackle new problems”, concludes the researcher.

The paper comes from a collaborative project between the Bosch i Gimpera Foundation of the UB and Goya in Aragon Foundation. The objective is to evaluate the use of new techniques to emit electromagnetic waves in non-destructive testing in order to analyse the pigments used in artworks.



C. Seco-Martorell, V. López-Domínguez, G. Arauz-Garofalo, A. Redo-Sanchez, J. Palacios y J. Tejada. "Goya’s artwork imaging with Terahertz waves". Optics Express, July 2013. DOI: 10.1364/OE.21.017800

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