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The use of gamma-rays, ions, X-rays, electrons, or neutrons is very common for imaging, characterization, and the preservation of cultural heritage materials. Their use provides, for example, knowledge about their composition, they are used as a biocide of organic materials, or for the consolidation of materials. Concerns about the eventual side-effects (immediate and future) induced by radiation in some of these materials are growing among the different communities involved. It is very important to join the expertise, knowledge, and concerns of each radiation group together with conservators to clearly study the eventual cause (mainly due to physico-chemical mechanisms) of these side effects, which can provoke the loss of critical analytical information. Quite often objects are made of heterogeneous or composite materials, so consequences of radiation on a very well-known material can change when other materials are involved. Also important is the documentation of the radiation procedures performed on the objects, including any potential visual side-effect. Such information can be crucial for future radiation experiments or to monitor changes along time. The known side-effects observed in a wide range of materials shows the importance of investing in more research and interdisciplinary work. Some examples are: - Colour changes in transparent materials due to trapping of electrons in the vicinity of impurities ; - Overdoses of radiation can break bonds, induce cross-linking or temperature effects which can modify important properties of materials and in extreme cases affect their mechanical integrity ; - Formation of radicals, which can trigger undesirable chemical changes, such as oxidation, leading to colour changes or surface erosion. - Radiation dosages for fungicidal treatments (typically 5 to 10 kGy) can generate side-effects in sensitive materials like paper. To avoid over-exposure, the main parameters (the radiation dose and the dose rate) must be carefully controlled during radiation and optimized following the ALARA approach. Also important is to control and register the environmental parameters and experimental conditions (inert gas, vacuum, low temperature, low moisture, etc.) that can effectively mitigate some adverse effects. For documentation purposes, it will be also important to unify and clarify concepts used within different communities. For example, a dose of 1 kGy could be considered high for the “ion beam community” but not high enough for the “gamma-ray community”, and more importantly, their effects on the materials under study can be totally different. In this work, examples of visible side effects induced by different types of radiation will be shown. Possible responsible mechanisms and ways of mitigation will be discussed, also focusing on non-visible side effects and suitable approaches to detect and record them for future analysis. All researchers involved in cultural heritage materials using radiation techniques should be aware of the possible side effects that such materials may suffer from radiation and the consequences for their (future) behaviour. Only by understanding the origin of such effects, it will be possible to create strategies, protocols, and risk analysis prior to exposure. Research programs involving different communities and training programs are needed to raise our understanding and transmit knowledge.

Journal of Art Historiography, 27

Analysis of over 180 historical documentary sources from 1600 to 1900 covering the cleaning of oil paintings established that the use of alkalis was mentioned in over 50% of references to aqueous cleaning. Alkalis could be employed as a paste with wood ashes and water or in the form of lye. Historical alkali cleaning recipes based on wood ashes were reconstructed and characterised using titration and in- ductively coupled plasma-atomic emission spectroscopy (ICP-AES). Results indicate that pH depends on the wood-ash source, the age of both the ashes and the lye, as well as on the proportion of ash to water. Reconstructions of lye solutions and wood-ash pastes were applied to naturally aged model oil paints and oil paintings. Their visual impact was investigated using high resolution imaging, and chemical changes were studied with infrared spectroscopy in attenuated total reflection (ATR-FTIR) and focal-plane array Fourier transform infrared spectroscopy (FTIR-FPA) as well as scanning electron microscopy equipped with energy-dispersive X-ray analysis (SEM-EDX). These latter investigations determined the presence of potassium within the upper layers of paint samples after exposure to wood ash lye. The potassium remained in the oil network after extensive water rinsing. This research adds information to our existing knowledge about historical cleaning methodologies and contributes to a better understanding of the current condition of paintings previously cleaned with alkalis.

The visual appearance of a painting is the result of variations in pigments, layers and layer thicknesses. An important role can be played by ground colour. The ground is the first preparation of the support before the actual painting. Medieval painters worked on white grounds. Coloured grounds appeared during the late 15th century in Italy before spreading to the northern part of Europe around 1550. Painters like Rembrandt or Rubens exploited dark or light coloured grounds to create spectacular, realistic effects. But how can we understand how they do this? To answer this question and add some quantifiable analysis, one needs to resolve the spectral reflectivity profile of a painting in three spatial dimensions. In addition, as the main intent is to relate the optical effects with colours, one needs to operate using visible light. The answer to these challenges is visible-light Optical Coherence Tomography (vis-OCT). In this study, we investigate the use of vis-OCT to measure the reflectivity profile of multi-layered paint samples in three dimensions. Using mock-up paint samples we prepared with two thin paint layers on a black and a white paper support, we measured the reflectivity profiles of the separate colours and of the superposed colours over either the black or white (back)ground. This paper first describes the signal processing involved in rebuilding the spectral reflectivity in three dimensions. Secondly, we will present the results obtained from the mock-up samples and draw conclusions on the possibility to discriminate colours in a three-dimensional context. All reflectivity measurements will be compared to a classical, commercially available hyperspectral imaging setup. This study is executed in the context of the NWO Down to the Ground Project. The results of the OCT measurements will be used by technical art historians and conservators for investigations into coloured grounds.

Additional file 2: Table S1. Artificial soiling composition. Adopted from an artificial soil mixture used by Ormsby et al. [43]. Table S2. Condition assessment tests. Table S3. Air abrasive trials. Visible cleaning and undesirable surface change at nozzle distance to surface. Table S4. Parameters A���F for evaluating the effect and efficiency of the cleaning systems. Table S5. Parameter G���I for evaluating the practical user-friendliness of the cleaning systems. Table S6. a Numerical rating of the free-liquid trials on M1-G. b Free-liquid trials on M1-Pu. c Free-liquid trials on M1-Pd.

Additional file 3: Appendix S1. Propagation of uncertainty for colour and gloss measurements.

Additional file 1: Figure S1. a Low-vacuum SEM���EDX of an oil paint from The Sun suggested a cobalt blue pigment (PB28 cobalt aluminate CoO��Al2O2, 2���27 ��m) and barium sulfate (probably synthetic, 0.8���3.5 ��m) extender in a drying oil-based medium. Greyscale threshold images suggested area fractions of 14���19% of filler to bulk paint (cobalt blue pigment and oil fraction). b Low-vacuum SEM���EDX of a ground from Alma Mater suggested calcium to be the major element, attributed to chalk (CaCO3) (probably manufactured). BSE images suggested spherical chalk particles c. 0.2���4 ��m, with most of the particles between 1 and 2 ��m. Figure S2. SEM secondary electron image of a polyurethane cleaning sponge (~ 100��) used for the control treatment. Figure S3. SEM secondary electron images of wheat starch, Arbocel�� A and Arbocel�� B. ~ 300�� magnification. Figure S4. Soft particle blasting set-up: oil free air compressor, nozzle with hand switch, air gun with Y-connector, air blaster, blasting cabinet (not shown) and soft abrasives (not shown). Main unit supplier: Deffner & Johann. Stipulated line = connection or continuation. Figure S5. CO2-snow cleaning set-up: dual gas Venturi nozzle, CO2-gas tank with pressure gauge, compressed air heater, foot switch, nitrogen gas (not shown), CO2 detector (not shown), fume hood (not shown). Main unit supplier: Applied Surface Technologies. Stipulated line = connection or continuation. Figure S6. Hydro-gel sheet with detail of high-water-retention nano-gel. Supplier: Center for Colloid and Surface Science. Aqueous cleaning solutions selected from the Modular Cleaning Program. Figure S7. Accelerated aged control mock-ups (M2): unsoiled (upper) and artificially soiled (lower). 60�� objective, Hirox RH-2000-3D digital microscope (Hirox Europe, Limonest, France). The soiled mock-ups demonstrate the darkening and mattening effect of soiling. Figure S8. a FTIR spectra of the chalk-glue ground mock-ups before (upper) and at the end (middle spectra) of ageing and bread cleaning procedures, and of the chalk-based ground of Munch���s Alma Mater (lower). The Si���O���Si stretching bands in the Munch sample at 1200���1000 (1190, 1150 and 1090 cm���1) were attributed to trace ultramarine pigments (Na, Al, Si, S confirmed with SEM���EDX). These and traces of Pb and Zn, possibly deriving from small additions of lead and zinc white, were excluded from the mock-up ground to simplify the composition. The band with a maximum at 1030 cm���1 (assigned to SO42��� or Si���O���Si stretching) in the spectra of the aged and bread cleaned unsoiled M2-G mock-ups is probably contamination. No corrections to spectra. b Surface ATR-FTIR of M2-Pu mock-ups before (red line) and at the very end (blue line) of ageing and bread cleaning procedures. The black line shows the FTIR spectrum acquired with transmission spectroscopy of a sample of cobalt blue bulk paint and of the blue oil paint from Munch���s The Sun. No corrections to spectra. c Surface ATR-FTIR spectra of the Pd mock-ups before (red line) and at the very end (blue line) of ageing and bread cleaning procedures, and of the blue oil paint of Munch���s The Sun (black line). The spectrum for the Pd mock-up has a weak abortion band at 870 cm���1 attributed to chalk from the ground layer. No corrections to spectra. Figure S9. a Velocity of SPB abrasive powders compared to compressed air alone. Average of ten measurements. Standard deviation as error bars. b Velocity of the CO2-snow stream compared to that of SPB with Arbocel�� A. Standard deviation as error bars. Figure S10. a���c Colour measurements1. Figure S11. a���c Gloss measurements2. Figure S12. Performance of cleaning systems on parameters (G���I) related to user-friendliness.

Performative methods are playing an increasingly prominent role in research into historical production processes, materials, and bodily knowledge and sensory skills, and in forms of education and public engagement in classrooms and museums. Such methods, which we refer to as Reconstruction, Re-enactment, Replication, Reproduction and Re-working(RRR), are used across fields in the humanities and social sciences, from history of science and technology, to archaeology, art history, conservation, musicology and anthropology, among other disciplines. There is much to learn from interdisciplinary methodological reflection. RRR raises issues of truthfulness and accuracy, draws attention to process and performance as well as practices of documentation and facilitates communication with broader publics.

This chapter addresses the potential of reworking experiments or recipes in educational settings. We reflect on educational practice in several university settings, which span the Liberal Arts and Science Program in Utrecht and a course for historians of science and technology at Johns Hopkins University to physics teacher education at the Europa-Universität Flensburg. The classroom use of RRR methods serves to teach the exploratory nature of science, and focuses the attention of students on materials and the sensory dimensions of experiments. Together, the three cases argue that the use of RRR methods in the classroom allows teachers to engage students in new ways, and offers students the opportunity to participate more meaningfully in research into the history of science.

In paintings conservation, reconstruction plays a role as a treatment, when it serves to complete the structural image of a lost or damaged area or object, and in research, where reconstructions are employed, for instance, to investigate the impact of conservation treatments or for their innovation. The conservation field has developed several strategies to deal with questions of validity, truthfulness and relevance. By example of a number of recent conservation and conservation research projects, this chapter discusses terminology adopted for reconstruction practices within the field, strategies developed by conservators to deal with ethical and practical issues surrounding the use of reconstructions, and relates these strategies to the ethical framework that guides conservators in their daily work.

Discussions regarding reconstruction, replication, or re-enactment in music can be fruitful only if musicians are experts in understanding the quality of the material with which they make their music: sounds. Such expertise can be acquired by analyzing and adapting the ways organists and organ builders deal with organ sounds, as each organ is an individual to a far greater extent than any other musical instrument. Organ builders discern how the thousands of pipes in an organ should sound and cooperate; organists have to able to understand the frames thus set. Generally speaking, it follows that composers’ intentions are subordinate to musicians’ and listeners’ ones: music is something that sounds.

Discussions regarding reconstruction, replication, or re-enactment in music can be fruitful only if musicians are experts in understanding the quality of the material with which they make their music: sounds. Such expertise can be acquired by analyzing and adapting the ways organists and organ builders deal with organ sounds, as each organ is an individual to a far greater extent than any other musical instrument. Organ builders discern how the thousands of pipes in an organ should sound and cooperate; organists have to able to understand the frames thus set. Generally speaking, it follows that composers’ intentions are subordinate to musicians’ and listeners’ ones: music is something that sounds.

This chapter addresses the potential of reworking experiments or recipes in educational settings. We reflect on educational practice in several university settings, which span the Liberal Arts and Science Program in Utrecht and a course for historians of science and technology at Johns Hopkins University to physics teacher education at the Europa-Universität Flensburg. The classroom use of RRR methods serves to teach the exploratory nature of science, and focuses the attention of students on materials and the sensory dimensions of experiments. Together, the three cases argue that the use of RRR methods in the classroom allows teachers to engage students in new ways, and offers students the opportunity to participate more meaningfully in research into the history of science.

The relationship between artists’ material choices, the preparation and application of materials, and the consequences – the appearance and material properties of the art-work – are studied using Historically Accurate Reconstructions Techniques (HART). This model provides a systematic means to evoke past practices. Reconstructions focus on a range of topics, from the flow properties of Van Gogh’s paint to the colour of natural chalk used in artists’ preparation layers. As the operator physically prepares and uses the materials, the steps towards the moment of painting are re-enacted. The products of the re-enactment, the documentation and the reconstruction itself, provide evidence – visual, physical and chemical ‒ for comparison with historic oil paintings.