ABSTRACT This research intends to enhance our understanding of the tin-glaze technology employed in seventeenth- and eighteenth-century Delftware and other tin-glazed earthenware in the Netherlands. The study provides a detailed description of the raw materials utilised in Dutch tin glazes and offers a schematic overview of the production process. Additionally, 39 dated historical recipes for tin glazes are used to compare and interpret changes in the quantities of raw materials within a temporal context. Weight percentages of raw materials – estimated for the final glaze – reveal significant changes over time. The study shows that changes over time mirror the rise and decline of the Dutch tin-glazed earthenware industry, reflecting economic shifts. Most tin - the costliest glaze material – was utilised between c. 1680 and c. 1720, and the highest glaze qualities were reported during this period, marking the peak of the Dutch earthenware production. Towards the end of the heyday, a decrease in tin usage coincides with mentions of lower glaze qualities. The superior glaze quality of Delftware tin glazes compared to tin-glazes of other tin-glazed earthenware in the Netherlands could not be traced back to specific formulations. Other factors, such as the quality of raw materials, likely contributed to the perceived visual superiority.

ABSTRACT Since 2003 the four surviving Ross Sea huts of the Heroic Era (1899 –1917) of Antarctic exploration have been the subject of a major programme of conservation by the Antarctic Heritage Trust of New Zealand, the Ross Sea Heritage Restoration Project (RSHRP). This paper describes how the RSHRP came to be and the key components which were identified and put in place for the project at its outset. It then explores the learning from and challenges of this significant project, and it critically considers the way in which the programme has been developed and delivered. The example of Scott’s memorial cross is used to illustrate the innovative approach of the RSHRP, and through the case study, the authors share both the successes (and in some cases the lack of success) of treatments, and the learning which has come from this.

ABSTRACT In a project to preserve photographic archives in Southeast Asia, the authors sought to develop sustainable solutions with low environmental impact, avoiding air conditioning and using locally available materials. Dry cabinets were tested and implemented to store a glass plate negative collection that was rehoused in envelopes and boxes made locally. The project took just over a year to complete, and two years of monitoring environmental conditions have shown that relative humidity can be stabilized at low levels. However, the dry cabinets are airtight to limit the introduction of moisture and dust, preventing air exchange. In order to avoid the build-up of degradation by-products released by the stored materials, and in particular off-gassing of acetic acid from the cellulose acetate-based photographs, the use of an adsorbent is necessary. To achieve this, a cellulose-based composite with particles of a porous hybrid inorganic/ organic solid, denoted as a metal–organic framework (MOF), at a very high loading over 70% by weight and shaped as a sheet of paper, has been prepared and tested. This special paper maintains acetic acid-free air in the cabinets and also helps to reduce the energy consumption by reducing the need for cool storage. This MOF paper composite traps small carboxylic acids and was found to be an appropriate solution for maintaining clean air in the dry cabinets or any other confined space or enclosure. Additionally, it can also be designed to trap other noxious pollutants such as hydrogen sulfide or formaldehyde, by choosing other MOFs.

ABSTRACT This study provides an evaluation of MS3, a reduced polycyclohexanone resin, with key considerations for use as a picture varnish including solubility, removability, colour, and gloss and the stability of these factors. MS3 was first produced in 2016 as a replacement for the discontinued MS2A resin which was widely used as a conservation-grade picture varnish. Films of MS3 resin were artificially aged using UV-containing and UV-filtered light, representing the effects of daylight filtered through glass, and indoor museum lighting conditions respectively. Changes in colour and gloss of light-aged samples vs. control samples were measured, and solubility/removability was evaluated using selected solvents applied by hand-rolled swabs. FTIR spectroscopy was used to explore chemical changes of the varnish films following light ageing with respect to control samples. Empirical observations were made regarding the handling properties of MS3 dissolved in Stoddard solvent, and its behaviour as a retouching medium and varnish. The results suggest that MS3 exhibits a slight yellowing and a moderate increase in the polarity of solvent required for removal. No significant colour or solubility changes were observed in MS3 varnish films artificially aged using non-UV light. The results suggest that MS3 is a good substitute for MS2A resin for use as a picture varnish or retouching medium, based on the parameters measured.

ABSTRACT Natural history collections preserve invaluable taxidermy specimens, which are prone to light-induced degradation, compromising their historical and educational significance. Restoration of these specimens to their original appearance through chromatic reintegration is imperative. The principle of reversibility mandates interventions that are modifiable or reversible without harming the original work, thereby preserving authenticity and enabling future conservation efforts. This study aims to identify the most suitable product for chromatic reintegration of a mammal taxidermy specimen, evaluate its fidelity to the original population, and assess its imperceptibility to the general public during exhibitions. Various products underwent rigorous evaluation for colouration, drying time, coverage, reversibility, safety, and resistance to light degradation. Accelerated aging tests using the Xenotest were conducted to simulate long-term light exposure. A beech marten taxidermy specimen was restored with the chosen dye, and its colour was compared against skins from the original population of the species. Public perception tests were conducted to gauge the ability of people to detect the chromatic restoration during exhibitions. Orasol® dye emerged as the optimal choice for chromatic reintegration, meeting criteria for colouration, reversibility, coverage, and resistance to light degradation. Despite its toxicity for aquatic organisms, it demonstrated promising results. Most colour measurements closely matched the original beech marten population, with minor hue deviations. Public perception tests confirmed the imperceptibility of the chromatic restoration, indicating its suitability for exhibition and educational purposes. This study highlights the importance of authenticity and imperceptibility in restoration processes, emphasizing the need for meticulous consideration of budget constraints in museum settings.

ABSTRACT In this study, we investigated the diverse range of materials used for sizing in Iranian paper manuscripts during the Timurid (fifteenth century) to Safavid (sixteenth century) and Qajar (nineteenth century) periods. Our approach combined historical analysis with scientific examination of reconstructed sizings. We reconstructed 15 sizing materials based on identified Persian historical recipes and analysed their physical, optical, and spectral characteristics. Additionally, we assessed their behaviour against the mould fungus Aspergillus flavus. The results revealed distinctive properties for each sizing material, shedding light on their potential applications in paper preservation. Furthermore, our investigation demonstrated variations in hygroscopicity, thickness, grammage, and ash content post-sizing. The sizing materials also exhibited different effects on paper reflectance properties. Additionally, our study revealed insights into the impact of sizing on burnished papers, indicating that the mechanical process of burnishing did not significantly alter the chemical composition or spectral properties of the paper, with only minor changes in brightness observed in specific cases. All tested sizing materials supported varying levels of mould growth, indicating potential implications for paper conservation. Our findings provide valuable insights into the historical practices of Iranian paper sizing and offer practical considerations for the preservation of paper manuscripts.

ABSTRACT This paper outlines the aim, methodology, and initial results of a joint initiative between two universities (Université de Kinshasa in Kinshasa, Democratic Republic of the Congo and Université de Liège in Liège, Belgium), two conservation training courses (Academy of Fine Arts of Kinshasa and École Supérieure des Arts Saint-Luc in Liège), and the Institute of National Museums of Congo. The Nous avons des lacunes (We have gaps) project plays on the notion of loss – both material and of knowledge – to involve communities in the construction of endogenous knowledge on the conservation of objects: a task to be carried out by the Congolese, for the Congolese. For many Congolese, concepts such as ‘museum’ and ‘conservation’ sound foreign, and the idea of cultural rights remains highly abstract and theoretical. The challenge is to transform the manifestation of these rights through conservation into a real tool for empowerment. The exhibition concept is two-fold: conservators explain what loss or material alteration has occurred in a specific object, and how they remedy it, thus arousing interest in a little-known profession. At the same time, they show and explain their own gaps in knowledge, and ask the public for information about the technique, function, use, naming, or names of the mystery object in the four national languages and numerous Congolese idioms. The Nous avons des lacunes project aims to highlight the role and involvement of communities and different social entities as active guardians of their heritage, by humbly admitting the lack of knowledge among professionals.

ABSTRACT The mosaic coving at the Grade II* listed Freemasons’ Hall in London is an example of a mosaic on an Art Deco steel-framed building. Microstructural and chemical characterisation of loose mortars and tesserae were undertaken to inform conservation efforts and advise whether a protective coating was needed to prevent further fading of gold gilding. Rigorous testing used optical imaging, scanning electron microscopy, field emission scanning electron microscopy, energy dispersive X-ray analysis, Raman spectroscopy, X-ray diffraction, and thermogravimetric analysis with differential scanning calorimetry. Laboratory evidence demonstrated the glass tesserae were created using traditional techniques. The glass tesserae were soda-lime-silica glass with lead. The gold glass tessera was produced in the ancient Roman style which included a glass cartellina layer, so further protective coating was not needed. Historical records confirmed sheets of mosaic tesserae were prefabricated in Italy. The grout and thin-set mortar were the same low hydraulicity mortar mix, which enabled mosaic tesserae positions to be adjusted as required. The bedding coat mortar was a hydraulic cement mortar that was applied on top of an early example of foamed mortar from 1932. This unique study analyses a traditional style mosaic that was installed during a pivotal point in construction history where foamed mortars and steel framed buildings were introduced. It demonstrates how archival research and laboratory testing of small-sized samples enhance the building’s significance and architectural interest by improving the knowledge of its history.

ABSTRACT Air quality in 36 Danish storage buildings was investigated, ranging from naturally ventilated historical buildings to modern purpose-built storage facilities, some with full HVAC climate control systems. Most were able to maintain a humidity level within 40–60% RH. The main deviations were for older heated buildings without humidity control, resulting in dry winter periods. Many modern stores were un-heated, which resulted in an annual average temperature about 12–13°C, and a high (>80) time-weighted preservation index (TWPI). The older buildings often struggled to maintain a moderate temperature, but experienced summer levels of 20–30°C. This lowered the TWPI considerably, typically to index 40–80. Concentration of organic acids in air was below 50 ppb for 22 sites, and only high (>100 ppb) for a few sites due to off-gassing from heritage materials. The outdoor pollutants ozone and nitrogen dioxide were mainly found in low concentrations indoors (<5 ppb) except for a few locations with forced but unfiltered air intake. Low-energy storage had the lowest energy consumption of <3 kWh/m3 annually, while repositories with traditional climate control systems were in the range of 10–30 kWh/m3. Information on energy consumption in storage buildings is sparse, and the authors call for more research. The most optimal solutions were offered by the modern low-energy buildings, where the best conservation conditions as defined by TWPI (high), pollution levels (low), and energy consumption (low) were observed, and where sustainable operation such as sharing space between several institutions was often practiced.

ABSTRACT St Agnes Museum, Cornwall, currently holds in its collections a paint box with a metal plaque reading ‘John Opie 1806’, containing pigments and other artists’ materials. John Opie produced hundreds of oil paintings until his untimely death in 1807 and was a well-known and successful painter of portraits and historical scenes. However, his work has been little studied, in comparison to his contemporaries such as Joshua Reynolds. This paper discusses the identification of the pigments in the paint box using infrared spectroscopy (FTIR-ATR), optical microscopy, scanning electron microscopy with energy dispersive spectroscopy (SEM-EDX), Raman spectroscopy (SERS) and X-ray fluorescence (XRF). Seven pigments have been identified as ultramarine, lead white, fustic and carmine lakes, carbon black (likely ivory), hematite, and burnt sienna, consistent with the bottle labels where present. The identification has been further confirmed using historical literature, which has shown that the pigments are likely to be contemporary with the stated date of 1806. This information adds to the body of knowledge about the artist specifically, and the artists pigments generally available at the time.