Protecting earthen heritage using a green strategy: a study about natural water repellents

Using earth as a construction material is an ancient technique that can be found around the world in monumental and vernacular architecture. However, its preservation is a challenging topic that clearly needs deeper research, especially from the conservation science approach. Earthen heritage is also associated with ancient maintenance techniques employing natural and local products still being used in some countries. Having those methods as a background, this paper proposes to adopt a green conservation strategy and a scientific approach, learning from traditional procedures to apply on earthen heritage. In the present research, three natural products – arabic gum, linseed oil and beeswax – were studied in terms of compatibility and efficiency with adobe specimens. The main results are critically discussed, and the main conclusions are exposed and compared against the common professional practice.PD/BD/114411/2016 is acknowledged. This work was partly financed by FEDER funds through the Operational Programme Competitiveness Factors (COMPETE 2020) and by national funds through the Foundation for Science and Technology (FCT) within the scope of project SafEarth PTDC/ECM-EST/2777/2014 (POCI-01-0145-FEDER-016737

The use of contact sponge method to measure water absorption in earthen heritage treated with water repellents

Earthen heritage represents an important legacy regarding construction history and technological development, with a significant cultural value that must be preserved. According to UNESCO, around 10% of the World Heritage is built using earth, and 57% of these heritage structures are in danger. Although the interest regarding earthen heritage has grown in the last few years, there is still a significant lack of knowledge in terms of material characterization, especially from conservation science point-of-view. In particular, tests regarding water absorption are always difficult to perform with a material that changes completely when in contact with water. Indeed, due to the presence of clay particles, a normal capillarity test is almost impossible to perform. Moreover, water is responsible for a significant number of degradation phenomena often found in earthen heritage. As a result, there is an urgent need to develop suitable water repellent treatments and to evaluate their efficiency. For this reason, this study focuses on the contact sponge method to assess water absorption rates for adobe and for rammed earth specimens treated with three different water repellents - siloxane, linseed oil, and beeswax. Two sets of specimens were prepared and tested, showing that this method can represent an effective way to measure initial water absorption in earthen materials, and promising results from the tested water repellent treatments were found.The support from grant PD/BD/114411/2016 is gratefully acknowledged. This work was partly financed by FEDER funds through the Operational Program Competitiveness Factors (COMPETE 2020) and by national funds through the Foundation for Science and Technology (FCT) within the scope of project SafEarth PTDC/ECM-EST/2777/2014 (POCI-01-0145-FEDER-016737)

Microchemical and microscopic characterization of the pictorial quality of egg-tempera polyptych, late 14th century, Florence, Italy

This paper explores the added value of micro-chemical and microscopic approaches to gather scientific evidence that can technically explain the pictorial quality of an egg-tempera painting, and underpin assessments that otherwise would be based on naked eye observations only. Demonstration is here provided via the interdisciplinary investigation of the original technique used by Giovanni del Biondo in the polyptych Annunciation and Saints (1385 ca), Galleria dell'Accademia, Florence, Italy. The exquisite surface appearance makes this panel painting remarkable compared to artworks by coeval artists. Imaging techniques (UV, IR and IR false color), non-invasive single spot techniques (XRF and FORS spectrometry) and analytical investigations on eight selected micro-samples (ATR-FTIR, GC/MS and Py/GC–MS, ESEM-EDS) were combined to retrieve the palette and identify organic binding media and a superficial coating layer. Stratigraphic and micro-chemical data confirmed the use of a relatively simple egg-tempera technique applied on a ground made of gypsum mixed with animal glue, without complex stratigraphic superimposition of preparation and pictorial layers. Various pigments were identified, among which is the precious lapis lazuli. While Py/GC–MS highlight that the coating is made of dammar resin and honey mixed with animal glue, the results allow us to state that the painting was not intentionally varnished by Giovanni del Biondo. These outcomes shed a new light on the technical knowledge of this polyptych, and prove how challenging is the attempt to categorize egg-tempera recipes used by ancient painters at the turn of the 14th century

Gold leafs in 14th century Florentine painting

Gold leafs are typically present in paintings and frescoes of the Italian Renaissance in the 13th and 14th centuries. The chemical composition and thickness of gold leafs provide important information toward a better understanding of the technology of that epoch. The present paper discusses the results of non-destructive analysis carried out with a portable energy dispersive X-ray fluorescence (ED-XRF) equipment on the 14th century panel Annunciation with Saints Catherine of Alexandria, Anthony Abbot, Proculus and Francis by the painter Lorenzo Monaco.L’application de feuilles d’or sur des tableaux et des fresques est typique de la Renaissance italienne aux xiiie et xive siècles. Leur composition chimique et leur épaisseur fournissent des informations importantes pour la compréhension des techniques de cette période. Ce travail discute les résultats des analyses non-destructives réalisées avec un système portable de fluorescence X à dispersion d’énergie (ED-FX) sur le panel du xive siècle Annonciation avec Saints Catherine d’Alexandrie, Anthony Abbot, Proculus et Francis par le peintre Lorenzo Monaco

A Bacillus subtilis cell fraction (BCF) inducing calcium carbonate precipitation: biotechnological perspectives for monumental stone reinforcement

Abstract Monumental stone decay is a consequence of the weathering action of physical, chemical and biological factors, which induce a progressive increase in porosity. To cope this degradation, bacterial calcium carbonate mineralization has been proposed as a tool for the conservation of monumental calcareous stones. The advantage of this kind of treatment is to obtain a mineral product similar to the stone substrate, mimicking the natural process responsible for stone formation. In this work, the possibility to induce CaCO3 mineralization by a bacteria-mediated system in absence of viable cells was investigated and tested on stone. Our results showed that Bacillus subtilis dead cells as wells as its bacterial cell wall fraction (BCF) can act as calcite crystallization nuclei in solution. BCF consolidating capability was further tested in laboratory on slab stones, and in situ on the Angera Church, a valuable 6th century monumental site. New crystals formation was observed inside pores and significant decrease in water absorption (up to 16.7%) in BCF treated samples. A little cohesion increase was observed in the treated area of the Angera Church, showing the potential of this application, even though further improvements are needed