No abstract

X-ray computed tomography is a common tool for non-destructive testing and analysis. One major application of this imaging technique is 3D porosity identification and quantification, which involves image segmentation of the analysed dataset. This segmentation step, which is most commonly performed using a global thresholding algorithm, has a major impact on the results of the analysis. Therefore, a thorough description of the workflow and a general uncertainty estimation should be provided alongside the results of porosity analysis to ensure a certain level of confidence and reproducibility. A review of current literature in the field shows that a sufficient workflow description and an uncertainty estimation of the result are often missing. This work provides recommendations on how to report the processing steps for porosity evaluation in computed tomography data using global thresholding, and reviews the methods for the estimation of the general uncertainty in porosity measurements.

Scanning electron microscopy (SEM) is a common method for the analysis of painting micro-samples. The high resolution of this technique offers precise surface analysis and can be coupled with an energy-dispersive spectrometer for the acquisition of the elemental composition. For light microscopy and SEM analysis, the painting micro-samples are commonly prepared as cross-sections, where the micro-sample positioned on the side is embedded in a resin. Therefore, the sequence of its layers is exposed after the cross-section is polished. In common cases outside of cultural heritage, a conductive layer is applied on the polished side, but in this field, the measurements are mostly done in low-vacuum SEM (LV-SEM). Although the charging effect is reduced in LV-SEM, it can still occur, and can hardly be prevented even with carbon tape or paint. This work presents two conductive cross-section preparation methods for non-conductive samples, which reduce charging effects without impairing the sample integrity.

Cross-section preparation of painting micro-samples is part of their routine analysis. This type of preparation can be used for several analytical techniques, such as scanning electron microscopy, Fourier-transform infrared spectroscopy, Raman spectroscopy, and optical microscopy. These techniques offer high-resolution imaging and/or elemental information, providing access to technical and material data important for the interpretation, preservation, and restoration of painted artworks. However, it also means that the material from the sample embedded in the resin becomes unreachable for further analysis, except for the polished surface of the cross-section. Degradation of the embedding medium can also occur over time, which can lead to misinterpretation, loss of information, or even complete destruction of the embedded sample. In the field of cultural heritage, cyclododecane (CDD) is commonly used for the consolidation and protection of objects, and is used in the preparation of cross-sections to prevent contamination of the sample by the embedding medium. This study enhanced the existing preparation process by shaping the CDD layer to enable extraction of the micro-sample from the resin if needed, without compromising the integrity of the sample. Moreover, the purity, the sublimation rate in a normal environment and a vacuum, and the impact of CDD on three different types of samples (historical painting on a canvas, wall painting fragment, model sample) were examined.

Chalk has been used since Antiquity for various purposes, and since Gothic for preparatory layers of painted cultural heritage objects. Several materials are called chalk in Cultural Heritage, but this work especially focuses on chalk composed of calcareous nannofossils (up to 98%). These are fossil remains of photoautotrophic algae generally smaller than 30 μm. They are mainly visible as platelets of various shapes under a cross-polarised or scanning electron microscope. The provenance of chalk can be determined using calcareous nannofossils due to their well-known paleobiogeographic localities. They are already used as proxies since the 90s in Cultural Heritage, but rarely for paintings. In this work, 6 chalk historical mining areas were chosen: Germany (Ruegen), France (Champagne, Meudon), Belgium (Mons), England (Norfolk) and Italy (Bologna). Natural and processed chalk were used as reference materials and compared to 3 original paintings. The difference between the chalks calcareous nannofossil assemblages was shown using multivariate statistical analysis based on species relative abundance. Marker nannofossil species were defined for each chalk locality. One painting material could not be originated due to the preservation of its nannofossils assemblage, but the origins of the rock chalk material from the two other paintings could be geographically located in France.

No abstract

The use of calcareous nannofossils for provenance analysis is a new-old topic for cultural heritage. Several studies have already mentioned it for ceramic, but less for paintings. Preparatory layers of the paintings are often made with chalk, which is composed of microfossils. To extract a calcareous nannofossils assemblage from a painting layer, we need to disaggregate it. The method is to plunge the micro-samples into water and heat it if water alone does not work. The disaggregation process takes a long time and is not efficient in terms of quantitative results. In this work, we aimed to develop a disaggregation method that increases the number of determinable nannofossils extracted from a painting micro-sample. As these samples are valuable and unique, we decided that a combination of analyses on the disaggregated micro-sample should be tried to extract the most information from it. We studied the possibility of binder determination by gas chromatography–mass spectrometer after the nannofossils assemblage extraction on the residual liquid from the disaggregation. The method we are presenting is easy to apply, has a high disaggregation rate for most paintings, and a low impact on binders fatty acids for their determination.

No abstract