Background

Identification of painting materials in works of art is a fundamental step for the understanding of an object’s history or an artist’s technique. A comprehensive characterization and diagnosis may provide significant evidence for dating, provenance attribution or forgery detection, as well as key information for an optimal conservation strategy. Artistic, stylistic, and physico-chemical features must be exploited in order to decode the authenticity of an object and specific problems and questions should be addressed depending on the object’s context. According to the Fine Art Experts Institute in Geneva, as much as fifty percent of the artworks currently in circulation may be forgeries. In this context, the applications of scientific methods to reveal fakes of art has seen an increase demand by collectors, museums and art galleries, moreover as authenticity is closely related with the artwork value. Current practice in the field of artwork authentication employs a combination of background knowledge (conducted on the grounds of style, technique and other artistic methods) and scientific data. Besides an in-depth view within the materials and painting techniques used by the artist, scientific data may also reveal information on physico-chemical features that are inconsistent with the supposed history of the artifact.

The scientific investigation of painted works of art is not an easy endeavor as paintings are unique and complex build-up structures created by superimposing paint layers. In principle a wide variety of complementary information may be obtained by integrating various techniques, the only limitations being the availability and cost of the analyses. Depending on the existing resources, appropriate investigation strategies must be developed to meet specific requirements given by the object in study. The analysis of paint layers of polychrome works of art represents a constant challenge within the cultural heritage field. Paint samples are most often characterized by a high degree of heterogeneity as each layer is a mixture of different compounds (pigments, binders, mineral fillers) that interact and change over time giving rise to severe difficulties in terms of the analytical capabilities to characterize these multicomponent and multiphase chemical systems. Another issue when studying such matrices is given by the difficulty to physically separate the different thin layers – usually between 10 μm up to 200 μm. Moreover, taking into account the necessity to preserve the integrity of the object, the amount of samples taken from an artwork is limited and often not representative of the entire artwork.

The characterization of paint layers in works of art has been intensively studied, best results so far being obtained by combining several non- and micro-destructive techniques. At this moment the range of analytical techniques available for painting research is fairly extensive, from well-established spectroscopic methods (FTIR, Raman, XRF) to gas chromatography coupled with mass spectrometry (GCMS), or chemical imaging techniques such as synchrotron radiation (SR)-based micro-X-ray fluorescence (μ-XRF). To complement the information obtained on possible micro-samples, portable versions of various non-destructive spectroscopic techniques are being used to gather targeted information in multiple locations. Combining elemental information from X-ray fluorescence with molecular and structural data from vibrational spectroscopies has become a standard approach. Depending on the amount and on the type (powder or fragment) of the available samples, micro-analytical methods can also be used (μ-FTIR, μ-Raman) especially for the characterization of thin layers and small particles. Such advanced analytical methods can determine the nature of the painting materials, reveal the painting technique, identify degradation pathways, or discriminate between the original materials and the ones used in previous restorations. Current directions in the field include development of new spectroscopic tools and integrated methods (coupling techniques) that can provide targeted information of cultural heritage materials non-invasively, on-site.

As works of art are often composed of multiple layers, an in-depth investigation requires data from across the painting’s surface, as well as depth profiles through the paint layers themselves. Subsurface layers may include underdrawings, underpaintings, and/or various types of alterations. Several non-invasive imaging methods have been developed and employed in recent years for surface and subsurface investigation of paintings such as macroscopic X-ray fluorescence (MA-XRF), macroscopic Fourier transform infrared scanning in reflection mode (MA-rFTIR), or hyperspectral imaging in the visible, near-infrared or short-wave infrared range. Limitations in fully resolving complex layer stratigraphy due to matrix effects are still among the open topics of research.

Objectives

The main aim of the INFRA-RT project is to foster innovation and knowledge advancement in the field of heritage science, with a specific focus on the scientific examination of painted works of art. The specific objectives of the present project are as follow: (O1) Development of an integrated spectral library of artists’ and cultural heritage materials; (O2) Workflow for material identification and discrimination (with a focus on historical pigments); (O3) Algorithm design for automatic classification and identification of painting materials using multivariate analysis; (O4) Development of integrated pigment-mapping techniques.

Impact 

Expected results of the project include: innovative results competitive at international level; integrative approach for the development of new solutions for the characterization, diagnostic and forgery detection of painted works of art; possibility to solve old problems within the heritage science field and stimulate new questions and research directions.