Mineralogical changes arising from the use of aqueous sodium carbonate solutions for the treatment of archaeological copper objects

Abstract

Mineralogical changes which occur during the reaction of copper(II) chloride with carbonate in aqueous solution have been investigated, and compared with those involving copper(I) chloride, nantokite, CuCI, and copper artifacts coated with malachite, CU₂CO₃(OH)₂ The reactions observed and the products obtained are seen to have implications with respect to the use of aqueous sodium carbonate solutions to stabilize archaeological copper objects. The frequent observation of the mineralogically rare species chalconatronite, Na₂Cu(CO₃)₂·3H₂O, on the surface of treated objects is readily explained by known reaction chemistry. Its formation can be minimized by washing the object after treatment.     

A Note on the Products of the Reaction of AMT with Bronze and with Three Corrosion Products of Bronze

Abstract

The compound 5-amino-2-mercapto-1,3,4-thiadiazole (AMT) is utilized in the conservation of archaeological and artistic bronze artifacts, for their protection and for the removal of corrosion products. Many authors have discussed the utility and efficacy of this, but few have studied the products resulting from the reaction of AMT with bronze or with the corrosion products of bronze; this leaves the restorer with many doubts concerning the acceptability of this method. This paper discusses the study of products obtained from the reaction of AMT with synthesized corrosion products of bronze (malachite, paratacamite and brochantite) and with the commercial bronze alloy TM 23 (Cu 72%, Pb 15%, Zn 8% and Sn 5%). It was found that the film obtained from the direct reaction of AMT with the bronze alloy can be AMT itself, or the metallic complex Cu(C₂H₂N₃S₂)₂·H₂O if AMT is applied in a solution of an oxidizing acid. These results are expected to be of value to conservation scientists and restorers/ conservators concerned with the use of AMT for the conservation of bronze artifacts.     

Pickeringite: A deleterious salt on buildings

Pickeringite, MgAl₂(SO₄)₄·22H₂O, was observed as efflorescence at the church of Saints Peter and Paul in Largario (Switzerland). The spongy salt crusts formed directly on rusty, deeply weathered gneiss rich in mica. The building stones originate from rocks in the vicinity of the village. On outcrops, similar occurrences were discovered. Ferrous and pyritic gneiss exhibited efflorescences of gypsum, epsomite, potassium alum, and pickeringite in sheltered places. Based on these observations and the known conditions of formation, we conclude that pickeringite resulted as a secondary mineral from weathering of pyritic gneiss. Most likely, weathering happened in an environment where, among other ions, aluminium and magnesium were present, but calcium and carbonate were absent. Such conditions rarely occur. If our hypothesis was confirmed, the fact that an extremely acid, calcium- and carbonate-free weathering system evolves next to lime mortars and plasters would be very surprising. It would imply that restricted zones devoid of a buffering effect develop on a microscopic scale.     

Kunsterhaltung - Machtkonflikte: Gemälde-Restaurierung zur Zeit der Weimarer Republik [Art Conservation - Conflicts of Power: the Conservation of Paintings during the Weimar Republic]

Abstract

The widespread occurrence of thecotrichite, Ca₃(CH₃COO)₃Cl(NO₃)₂·7H₂O, in the museum environment is explained theoretically by construction and examination of its phase diagram. Thecotrichite formation was simulated in the laboratory to identify the key factors involved in its production. This efflorescence occurs on porous limestone or calcareous artefacts such as pottery, stored in wooden cabinets that generate acetic acid vapour. Salt production depends on the moisture content of the object and the concentration of acetic acid in its surroundings. Furthermore, for thecotrichite to form the artefact must contain soluble chloride and nitrate salts.     

The iron in black weathering crusts on Saxonian sandstones investigated by Mössbauer spectroscopy

Abstract

Black weathering layers on stone often contain iron. This is particularly true for the Turonian sandstones which were used extensively in architecture and sculpture in Saxony. In order to obtain more knowledge about the oxidic iron phases, samples were collected in the city of Dresden. Mineralogical and analytical characterization was provided for the black layers and the supporting stone. Material originating from Cotta and Posta stone was submitted to Mössbauer spectroscopy. After ample comparisons of Mössbauer parameters and evaluation of infrared spectra it was concluded that the predominant neogenic iron phase is not iron(III) oxide hydrite (ferrihydrite) Fe₂O₃·1·8H₂O or jarosite KFe₃(SO₄)₂(OH)₆ or goethite α-FeO(OH) but a defectively ordered precursor of this last compound, characterized by different environments of the iron(III) ions. By the reducing action of organic matter, magnetite Fe₄O₄ is formed and this contains up to 45% of the iron present in a black layer.     

Lammerite as a Degradation Product of Emerald Green: Scientific Studies on a Rural Persian Wall Painting

Pigments on a figurative wall painting in Poudeh village, central Iran, were analysed by micro X-ray fluorescence spectrometry, micro Raman spectroscopy, scanning electron microscopy coupled with energy dispersive X-ray spectrometry, micro Fourier transform infrared spectroscopy, X-ray diffractometry, and polarised light microscopy. Red lead, ultramarine blue, chrome yellow, brass powder, white huntite, and lammerite (Cu₃(AsO₄)₂) were identified as red, blue, yellow, golden, white, and green pigments, respectively, while gypsum and barite were used as extender. In addition, glushinskite (MgC₂O₄·2H₂O) was identified as a deterioration product of white huntite. Moreover, several analytical studies suggested that lammerite was a degradation product of emerald green (Cu(CH₃COO)₂·3Cu(AsO₂)₂) originally used as green pigment in the painting. The formation of lammerite is suggested to be due to the migration of arsenic throughout the paint layer. Based on the pigments identified, the wall painting is dated from the mid-nineteenth century to the mid-twentieth century.     

When Glass and Metal Corrode Together,VI: Chalconatronite

ABSTRACT

Chalconatronite, Na₂[Cu(CO₃)]₂·3H₂O, is formed as a corrosion product when copper alloys are exposed to sodium carbonate solutions in the air. This also happens when metals come into contact with corroding soda glass which forms alkaline surface films in reaction with humidity from clean air. More often, substantial amounts of formaldehyde are present indoors which react to formate via the Cannizzarro reaction and accumulate over time in the films. Twenty cases of chalconatronite (including two mentioned in the literature) are reported as occurring on heritage objects with glass in contact with copper alloys: Baroque reliquaries with set glass gems, enamel on metal (sixteenth century and a modern replica of intentionally unstable composition), Christmas tree glass baubles with wires, glass buttons with metal shanks, a glass figure with a wire support, miners’ lamps, and a glass framed daguerreotype. These confirmed identifications might help conservators in investigating similar cases to shed more light on the formation conditions.     

The conservation of lead communion tokens by potentiost atic reduction

Abstract

The paper discusses the methodology adopted for and the results derived from a pilot project to conserve the lead and lead alloy communion tokens in the collections of St Andrews University. For the project a new conservation process, ‘potentiostatic reduction’, was developed, involving reduction of the tokens at ?1·2V vs. SCE (saturated calomel electrode) in 0·5M H₂SO₄, The aim of the pilot project was to test the effectiveness of the new process in tackling a largescale conservation problem by observing its effects on a wide range of tokens made of various alloys and suffering from varying degrees of corrosion. The results of the pilot project indicated that potentiostatic reduction is as effective as standard electrolytic reduction. Since the new technique greatly reduces the time required for the conservation of individual artifacts, there are substantial savings in conservation costs.     

Degradation of Emerald green in oil paint and its contribution to the rapid change in colour of the Descente des vaches (1834–1835) painted by Théodore Rousseau

Abstract

Descente des vaches (1836) by Théodore Rousseau in the Mesdag Collection in The Hague is barely readable and its paint layers are in poor condition. The surface of the painting is strongly deformed and cracked, the whole painting has darkened and especially the greens have lost all or most of their colour resulting in brown passages. Large passages of the painting that were painted with multiple thick and medium-rich layers have darkened dramatically. This paper proposes that the degradation of Emerald green (Cu(C₂H₃O₂)₂·3Cu(AsO₂)₂, copperacetoarsenite) – the main green pigment used in this painting – is a significant factor in the cause of the darkening. Electron backscatter images reveal that the Emerald green particles are shown different degrees of degradation: from partially to completely disintegrated. Elemental maps show that arsenic is distributed throughout the paint cross section, with relatively higher concentrations around iron- and aluminium-containing particles, and in the varnish layer. Imaging-Fourier-transform infrared microscopy detects copper soaps in the degraded Emerald green-containing layers. Analytical data from four paint cross sections strongly suggest that Emerald green reacts with free fatty acids derived from the binding medium forming copper soaps and mobile arsenic-based species. Chemical laboratory experiments fully support this hypothesis. Emerald green and palmitic acid in chloroform form copper palmitate and arsenic trioxide (arsenolite, cubic) under room temperature and normal light conditions. The degradation of Emerald green particles in Descente des vaches has resulted in a loss of light-reflecting surfaces and in newly formed compounds in the paint, both contribute to the colour change from green to brown.     

Impacts of consolidation procedures on colour and absorption kinetics of carbonate stones

The aim of this research work was to test the influence of stone properties, consolidation product, and application procedure on the potential harmfulness of consolidation on carbonate stones as assessed through the impacts on colour and water absorption kinetics. This article contributes to understanding the immediate and delayed impacts of consolidation treatments through the assessment of colour variation and modification of water absorption kinetics. The investigation was carried out on two limestones having a porosity of 10 and 27%, which were treated with three consolidating products (ethyl silicate, acrylic, and epoxy resins) using three treatment procedures: capillary absorption, brush, and full immersion. All products showed negative impacts at different degrees. We could show that their impact on a given stone depends not only on the consolidant type, but also on the treatment procedures. We demonstrated this way that the assessment of the potential harmfulness of a consolidation treatment for a specific intervention should be carried out in conditions as similar as possible to those expected to occur in practice and should never be based on extrapolations made from any other different conditions. The results also contribute to the definition of standard testing protocols in stone consolidation, privileging the application of a consolidant by direct contact capillary absorption when reproducibility is pursued, or by brushing when the potential highest impacts on colour are the target to evaluate.     

When Glass and Metal Corrode Together,V: Sodium Copper Formate

A sodium copper formate, first described in 2002, can also form on copper alloys with sodium originating from soda glass hydrolysis. The frequent occurrence (50% of 250 cases of glass-induced metal corrosion) is due to the presence of formaldehyde emissions in storage and its direct reaction to formate in the alkaline surface films. The compound can be produced without the presence of acetate when chalconatronite or metal coupons immersed in soda solution are exposed to formaldehyde vapours. The crystal structure, derived from X-ray powder diffraction, yielded the sum formula Cu₄Na₄O(HCOO)₈(OH)₂·4H₂O. Except for the absence of acetate in the structure, this is in good agreement with the 2002 publication. To assess which kind of combined glass/metal objects are affected, a number of large museum collections were surveyed. Sodium copper formate was detected as a corrosion product using mainly micro-Raman spectroscopy, for instance, on 18 painted Limoges enamels, eight glass vessels with metal mountings, glass beads on metal wire from 11 bridal crowns, nine Christmas tree balls with wire decoration, 40 pieces of jewellery with glass gems, three daguerreotypes, and one miniature with cover glasses.     

Characterization,weathering, and protection of sandstones: The case of ‘Agro d'Ardesia’

Abstract

The conservation of roofing and cladding materials has both environmental and cultural heritage bearing. Our research aimed at comparing the performances of some polymeric products used for the protection of a typical Italian sandstone, the ‘Agro d'Ardesia’, used mostly as cladding, paving, roofing, and building material. These products belong to three different classes: polysiloxanes, acrylics, and fluoropolymers. In addition, an acrylic–silicone mixture was chosen for testing. After the application onto the Agro sandstone by capillary absorption, both efficacy and durability were assessed. Particularly, two types of weathering tests were performed to check the stability over time of the protective products: the exposure to ultraviolet radiation in a climatic chamber and the ageing by exposure to acid rain, expressly designed to represent realistically natural and anthropogenic changes. Detailed information on treatment performances was obtained. The polysiloxane was shown to be the most effective protective material for the Agro sandstone.     

Copper vanadate minerals found in mediaeval mural paintings

Abstract

A yellowish copper vanadate mineral has been found in Swedish mural paintings from the fifteenth century. Small patches occur in malachite-green paint. Thirteen samples from five churches have been analyzed by optical and scanning electron microscopy with energy–dispersive X-ray spectrometry, transmission electron microscopy, X-ray powder diffraction, and polarized light microscopy. The substance is evidently the rather uncommon mineral volborthite, with the chemical formula Cu₃V₂O₇(OH)₂.2H₂O. Very small quantities have also been noted for another mineral, presumably calcio-volborthite, CaCu(VO₄)(OH), also named tangeite. The results show that the conservator should always be observant for pigments not earlier noticed or reported. There are some old mines in Central Europe, e.g. in Germany, which contain malachite as well as copper vanadate minerals, and this is probably the origin of the yellow patches in the paintings.     

Nineteenth century chrome yellow and chrome deep from Winsor & NewtonTM

The Winsor & Newton^TM (W&N) nineteenth century archive database includes digitised images of hand-written instructions and workshop notes for the manufacture of their artists’ materials. For the first time, all 183 production records for yellow lead chromate pigments were studied and evaluated. They revealed that W&N produced essentially three pigment types: lemon/pale based on mixed crystals of lead chromate and lead sulphate [Pb(Cr,S)O₄]; middle on pure monoclinic lead chromate [PbCrO₄]; and deep that contains the latter admixed with basic lead chromate [Pb₂CrO₅]; accounting for 53, 22, and 21% of the production, respectively. Production records for primrose (4%) were also included since the formulation results in mixed crystals with a high percentage of lead sulphate, which, according to the literature, leaves it more prone to degradation. Each pigment type is characterised by only one or two main synthetic pathways; process variations reveal a systematic and thorough search for a high-quality durable product. A comparison of the chemical composition of pigment reconstructions with early W&N oil paint tubes showed that their records entitled ‘pale’ and ‘lemon’ correlated with the pigment in their tube labelled chrome yellow and, ‘middle’ and ‘deep’ with the label chrome deep. Lemon and middle pigment formulations were made into oil paints to assess their relative photo-stability. The degradation process was followed by colorimetry and was studied by synchrotron radiation-based techniques. Based on the X-ray absorption spectroscopy data, the possibility for creating a stability index for chrome yellows is discussed.     

Marine Aerosol Weathering of Mediterranean Calcarenite Stone: Durability of Ethyl Silicate,Nano Ca(OH)2, Nano SiO2, and Nanostructured Consolidating Products

ABSTRACT

Calcarenite stone samples from a historic building (Bizerte, Tunisia) were collected and treated under different environmental conditions with several consolidating products: alkoxysilane (ethyl silicate), a surfactant-templated novel sol–gel, Ca(OH)₂, and SiO₂ nanoparticles. These were subjected to marine aerosol accelerated aging cycles and studied by several non-destructive tests and techniques to assess the stability of the products. Results show that weathering caused by salt crystallization is not inhibited but it is slowed down due to the enhancement of superficial mechanical properties (surface cohesion and micro-hardness) achieved after one month of treatments application. A high or low relative humidity of the consolidation environment significantly affects the final mechanical and aesthetical physical properties and therefore conditions the durability of the treated substrates, even producing higher damage than observed in the blank specimens, depending on the product.     

Controlling the aeolian erosion of the Great Sphinx

Abstract

The body of the Great Sphinx has suffered severe weathering, exfoliation and wind erosion; the face is not reached by coarse granules and is well preserved. The body lies below the level of the desert, and the excavated area that surrounds the Sphinx constitutes a low-pass filter for the size of the sand grains. In past millennia, when the Sphinx was immersed in the floating sand dunes, severe wind erosion was caused by the coarse quartz granules that advance by saltation in the first metre above the variable sand level. Clearing out the excavated area has proved to be an effective preservation technique.     

THE CONSERVATION OF PYRITIC STONE ANTIQUITIES

Abstract

The occurrence and identification of ‘fossil disease’ in stone artifacts is described, together with details of techniques for the stabilization and consolidation of the specimens.     

Ratios of h-cores,h-tails and uncited sources in sets of scientific papers and technical patents

Five ratios R_H, R_T, S_H, S_T and S_Z derived from the three-part division of a set of sources in h-core, h-tail and uncited sources are defined. Dynamic changes in the three independent ratios R_H, S_H and S_Z are studied for six selected topics. Data about these topics are obtained from the Web of Science for scientific papers and Derwent Innovations Index for technical patents. It is observed that all R_H- and S_H-values decrease when the time span widens, while S_Z stays the same or increases; and that all R_H- and S_H-values for papers are larger than the corresponding values for patents. The shifted Lotka distribution is used in a theoretical interpretation of these empirical phenomena.     

Scientific storytelling: A narrative strategy for scientific communicators

Courses: Science communication, public speaking, technical communication, professional and/or management communication

Objectives: This activity about scientific and technical communication uses narrative principles to communicate complex information to broader audiences. Upon completion of the activity, students will be able to:

• (1)?Explain the four fundamental elements of Cohen’s framework for creating memorable anecdotes.

• (2)?Identify the four elements of Cohen’s framework in sample scientific presentations.

• (3)?Provide examples of how to apply Cohen’s framework to communicate complex information.

• (4)?Identify one or two complex concepts in their subject area that would benefit from a narrative approach.

• (5)?(Optional) Use Cohen’s framework to create a narrative relevant to their subject area.

     

A TREATMENT FOR BLANCHING IN PAINTINGS

Abstract

The best material to be used in the restoration of a work of art is that most similar to the original. When grouting of lime-based wall paintings is necessary, lime-based grouts are the obvious choice. Compatibility is particularly important for grouting, as this is an irreversible operation. To set, lime-based grouts need air, specifically carbon dioxide, CO₂. However, in the narrow space between two delaminating layers where the grout is injected, CO₂ is not usually available in large enough quantities for this process to occur satisfactorily. To overcome this problem, extensive use has been made of hydraulic grouts, which set with water, and grouts containing synthetic or natural organic binders. A search was conducted for additives that would facilitate the setting of lime-based grouts, even at low CO₂ concentrations. In this study, a group of substances that produce CO₂ by reacting with water in an alkaline environment, esters of carbonic acid, were identified and tested to understand the kinetics of the setting process. Additives that would increase the fluidity of the grouting mixture, thus improving its injectability, were also investigated. The practical application of these grouting mixtures is illustrated by the recent restoration of Masaccio and Masolino's frescoes in the Brancacci Chapel in Florence.