Optimum spectral window for imaging of art with optical coherence tomography

Optical Coherence Tomography (OCT) has been shown to have potential for important applications in the field of art conservation and archaeology due to its ability to image subsurface microstructures non-invasively. However, its depth of penetration in painted objects is limited due to the strong scattering properties of artists’ paints. VIS-NIR (400 nm – 2400 nm) reflectance spectra of a wide variety of paints made with historic artists’ pigments have been measured. The best spectral window with which to use optical coherence tomography (OCT) for the imaging of subsurface structure of paintings was found to be around 2.2 μm. The same spectral window would also be most suitable for direct infrared imaging of preparatory sketches under the paint layers. The reflectance spectra from a large sample of chemically verified pigments provide information on the spectral transparency of historic artists’ pigments/paints as well as a reference set of spectra for pigment identification. The results of the paper suggest that broadband sources at ~2 microns are highly desirable for OCT applications in art and potentially material science in general

Malachite pigment of spherical particle form

Malachite of spherulitic particle form is generally thought to be synthetic in origin. However, it could be mineral malachite formed by natural precipitation from flowing water. Agricola described a source of this type in Neusohl (Banská Bystrica, Slovakia) in 1546. This hypothesis was considered by evaluation of historical documentary sources on green pigment production in the Neusohl region, and the geological literature. Precipitation experiments imitating the natural conditions produced malachite of spherulitic form, and several wall paintings in Neusohl were found to contain spherulitic malachite. Evidence that these, and examples from Italian paintings, could be from a naturally precipitated source is presented

New insights into the materials of fifteenth- and sixteenth-century Netherlandish paintings in the National Gallery, London

Abstract The long-term programme of technical examination conducted at the National Gallery, London, during cataloguing of the Netherlandish School paintings surveyed the materials and techniques of a wide range of artists, including not only Van Eyck, Van der Weyden, Bosch, Bruegel, Massys and Gossaert but also lesser known painters from the same period. The research presented in this article brings together both published and unpublished results from this project, strengthening the trends that had been emerging and bringing new insights into the development of artists’ materials over this period. A notable finding during the programme was the discovery of two paint additives—colourless powdered glass and zinc sulphate (white vitriol)—probably added as driers. The new quantitative analyses of the glass composition presented here add to those already published, and reveal that towards the end of the fifteenth century high lime–low alkali glass begins to be used. This observation holds the potential to contribute to questions about the dating of Netherlandish paintings. A smaller number of occurrences of zinc sulphate were identified suggesting that it was less common than glass as an additive, but it is nevertheless significant since it was used by a key figure in the history of oil painting, Jan van Eyck, and occasionally, where present in excess, has caused conservation problems such as drying defects in the paint. Occurrences of the unusual pigments vivianite and fluorite were identified in a few sixteenth-century works. The main changes encountered during the period, however, were the introduction of the blue pigment smalt, its instability having consequences for the current appearance of the paintings, and of a green copper mineral pigment composed of mainly copper sulphate. The latter has proved to be far more common than had been realised in the past

Investigation of the loss of colour in smalt on degradation in paintings using multiple spectroscopic analytical techniques

International audienceSmalt is a potash glass with a blue colour given by cobalt, common as an artists' pigment between the 16th and 18th centuries. It often deteriorates, losing its colour and causing dramatic changes in the appearance of paintings. The changes in structure and elemental composition accompanying the loss of colour in the glass were examined in samples from paintings in the National Gallery, London and the Louvre using synchrotron micro Xray absorption spectroscopy, synchrotron reflectance FTIR microspectroscopy, Raman microspectroscopy and SEM-EDX. The leaching of potassium was found to be responsible for concurrent structural modifications in the glass: increase in polymerisation of the silicate network and change in cobalt coordination from tetrahedral towards octahedral, leading to colour change in the pigment. These results also form valuable reference data for examinations with lab-based techniques to distinguish between smalt that is degraded or a pale grey variety deliberately chosen by the artist. résumé Le smalt est un verre potassique dont la couleur bleue est due au cobalt, communément employé comme pigment par les artistes du xvi e siècle au xviii e siècle. Il se détériore souvent, en se décolorant et en entraînant des modifications radicales dans l'apparence des tableaux. Les changements de structure et de composition élémentaire qui accompagnent la décoloration du verre ont été examinés sur des échantillons provenant de tableaux du Louvre et de la National Gallery, à Londres, par microspectroscopie d'absorption X pa

Vibrational spectroscopy correlated with elemental analysis for the investigation of smalt pigment and its alteration in paintings

International audienc