The problem of formaldehyde in museum collections

The release of formaldehyde from plywood, particleboard, coatings, and insulating matérials containing formaldehyde-based resins is referred to by the mobile home and foam insulation industries as ‘the odor problem’, but it is a suspected carcinogen.¹ These formaldehyde-containing materials are widely used in the construction of new museums and redesigned exhibition and storage areas; but only recently has formaldehyde begun to be identified as a danger to museum collections. It is widely known that formic and acetic acids, which can be released by wood products, may cause serious damage to lead-containing alloys and other metals, stone, ceramics, shell specimens, and organic materials.² Some of this corrosion, which usually is in the form of a white crystalline growth, may be attributable to formaldehyde, as discussed below. The authors conducted a survey of conservation, industrial, and environmental literature to determine the potential for and the nature and extent of damage caused by the presence of formaldehyde in museum construction materials. Although industrial literature contains much information on the use of formaldehyde and formic acid for alteration of the properties of both organic and inorganic materials, there is little information in the conservation literature about the potential for similar alteration of art materials. This research outlines the potential and actual effects of formaldehyde on works of art, and suggests some methods of avoiding these effects.     

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.     

A passive tube-type sampler for the determination of formaldehyde vapours in museum enclosures

Abstract

A tube-type passive sampling method has been developed and assessed for the quantification of formaldehyde (methanal) vapours in indoor air. The sampler was designed for use in museums where test sites often include small enclosures with low air movement. The procedure involves collection of formaldehyde vapours in a Palmes diffusion tube containing a paper support impregnated with an acidified solution of 2,4-dinitrophenylhydrazine (2,4-DNPH). After sampling, quantification of the trapped F-DNPH is achieved by high performance liquid chromatography (HPLC) analysis with UV detection at 350nm. To validate the procedure, permeation devices were used to generate formaldehyde-containing atmospheres, 81–2975ppb, in a 20dm³ chamber so that experimentally derived sampling rates could be calculated and compared with the theoretical value. Three 2,4-DNPH solutions were investigated to obtain an efficient and stable trapping solution. Best results were achieved with a 27mg.ml^?1 solution of 2,4-DNPH which contained 4·5%v/v orthophosphoric acid. At 55% RH, and with low airflow in the chamber, the experimentally derived sampling rate of 1·34 ± 0·17ml.min^?1 was in good agreement with the theoretically derived sampling rate of 1·36ml.min^?1 The passive sampling method was repeatable and reproducible with RSD (relative standard deviation) values below 7%for long-term exposures at low air velocities.     

After Eighty Years: Experimental Study of Atmospheric Corrosion in the Metallic Dome of Hafez’s tomb,Shiraz, Iran

ABSTRACT

Hafez’s tomb was constructed on the grave of the well-known Iranian poet in Shiraz, in the 1930s. The dome of this monument is made of copper metal and has been exposed to the urban environment for 80 years. In this study, corrosion mechanisms and conservation conditions of the metallic dome of the Hafez’s tomb are investigated by analytical methods including optical microscopy, ICP-MS, SEM-EDX, and X-ray diffraction. The results showed that the dome is constructed from many copper sheets that are hammered to shape the dome. The corrosion products formed on the surface of copper sheets include copper oxide and copper trihydroxichlorides. In fact, the corrosion mechanism occurring in the metallic dome consists of copper oxidation and redeposition of copper II products because of reaction with air pollutants.     

Characterization of stone from the Metropolitan Cathedral and from the facade of the National Museum at Tepotzotlan,Mexico

Abstract

The deterioration of stone monuments in urban atmospheres mainly involves corrosion by acid solutions. Thus the characterization of the material is of great importance in the understanding of stone decay. In this work, samples were taken from the balcony of the Metropolitan Cathedral (Mexico City), from three different areas of the facade of the National Museum of Tepotzotlán (NW of Mexico City) and also, for comparison, new fresh stone from the quarries of Chiluca and Los Remedios. Mineralogical, petrographic, chemical and structural analyses were carried out on all the samples, and a relationship was established between the degree of decay and the stone characteristics, such as porosity, specific surface area and calcium content. The characterization of the type of stone also influences the selection of conservation treatments.     

Characterization of the corrosion layer on iron archaeological artefacts from K2 (825–1220 AD), an archaeological site in South Africa

Abstract

A study of the composition and phase distribution of the corrosion layers on three ferrous objects, excavated at K2 (Bambandyanalo), an archaeological site in South Africa, was conducted. The objective of the study was to obtain information that can contribute to conservation procedures to be performed on the iron artefacts from this site. Examination of cross sections by means of energy-dispersive X-ray spectroscopy coupled to a scanning electron microscope (SEM–EDX), X-ray powder diffraction (XRD), and micro-Raman spectroscopy revealed the same corrosion composition and structure for all the objects under study, namely an internal layer adjacent to the metal surface with ghost inclusions and an external layer containing quartz grains. The study also revealed that the presence of magnetite (Fe₃O₄), maghemite (γFe₂O₃), and lepidocrocite (γ-FeOOH) within the internal layer is the only difference between the chemical compositions of iron corrosion products within the two layers. The results also made it possible to retrace the corrosion history during burial and long-term storage.     

ABSTRACTS

Abstract

The deterioration of Bronze Age objects from the archaeological site at Fort-Harrouard (France) has been studied, firstly, in relation to their external appearance and the elemental composition of the sound metal. A relationship between the composition of the corroded surface and the underlying sound metal was deduced. In addition, examination of metallographic sections of one of the bronzes allowed the differentiation of corrosion processes which are related to the shape of the object: the stratification of the corrosion products and the intergranular and transgranular corrosion processes. The existence of a pseudomorphic microstructure suggests that the mechanism of deterioration may be stratigraphic, which may be explained by the growth of the corrosion products in fissures which do not involve periodic precipitation.     

Study of Fe(II) sulphides in waterlogged archaeological wood

Abstract

Wet organic archaeological materials extracted from seawater may suffer damage as a result of degradation influenced by micro-organisms. One of the most common phenomena is indirectly induced by sulphate-reducing bacteria (SRB). Due to their metabolic activity in anoxic conditions, SRB generate hydrogen sulphide from sulphate ions present in seawater. When steel items are in contact with organic matter in presence of sulphides, corrosion of the metal leads to the precipitation of Fe(II) sulphides. These phases are responsible for dramatic post-excavation damage: their oxidation during storage or exhibition in museums leads to the formation of voluminous crystals, which may cause cracking and crumbling, and lead to the production of sulphuric acid. In order to characterize Fe(II) sulphides and their by-products, 13 waterlogged samples were analysed by environmental scanning electron microscopy, micro-Raman spectroscopy, and X-ray diffraction. Experiments were performed on untreated wood fragments, on a fragment of rope, and on mineral concretions scratched from the surface of wood remains, all extracted from different shipwrecks. Mackinawite was detected inside the fragments and between the fibres of the rope. Greigite was detected in scattered locations. Pyrite and sulphated phases, like gypsum and iron sulphates, were identified at the surface of the wood fragments and in the mineral concretions.     

Technical Analysis of an Early Painting by Botticelli

Abstract

A study is presented of the growth of sulphidecontaining corrosion products on antiquities in museums. Analysis of the corrosion products suggests that they are dependent on the mode of formation. Techniques for conservation have also been investigated and l-amido-l-cyanoethylene, 2,2-di(sodium thiolate) is recommended for dissolving the sulphide layers, while a treatment with benzotriazole followed by lacquering is recommended for long-term protection.     

CORROSION AND CONSERVATION OF A SILVER VISCERAL VESSEL FROM THE BEGINNING OF THE SEVENTEENTH CENTURY

Abstract

Two different cleaning methods were found necessary to remove silver chloride corrosion products from different areas of a silver canopic vessel containing about 6% of copper. Two possible mechanisms of silver corrosion which could have led to the differing silver chloride corrosion products are put forward.     

Eleanor Swenson Quandt 1921–2002

Abstract

Ancient bronzes in the collection of the J. Paul Getty Museum are maintained in low-humidity environments to eliminate the possibility of recurring chloride corrosion. A small, low-power, solid-state air drier was considered as an option to silica gel. This relatively new technology combines electrolytic dissociation of water molecules to hydrogen and oxygen with membrane separation. Hydrogen atoms formed on the anodic side penetrate the membrane and combine with oxygen on the cathodic side to form water. Oxygen atoms that remain on the anodic side recombine to form oxygen molecules. The process of water removal was found to be very efficient, but it is suggested that a portion of the oxygen atoms might react further to form ozone, a reactive molecule generally regarded as a deleterious pollutant in museum atmospheres. This was confirmed by passive sampling for ozone using diffusion tubes. While control levels after 60 days ranged from 0.43 to 1.25 parts per billion (ppb), samplers in the test environment recorded a level of 10.5 ppb, an increase of approximately 10 to 25 times. Developments in solid-state driers may overcome this problem in the future.     

Evaluation of sodium nitrite as a corrosion inhibitor for USS Monitor artifacts

Abstract

The use of sodium nitrite (NaNO₂) as a corrosion inhibitor for wet archeological metal objects presents potential advantages of near neutral pH, low concentration, effectiveness on several metals, and compatibility with organic materials. The effectiveness of NaNO₂ as a corrosion inhibitor for storage of chloride-containing marine archeological metal objects from the wreck of the USS Monitor was evaluated using marine-corroded carbon steel analogs. The samples were tested in varying concentrations of NaNO₂ and evaluated visually and by monitoring solution chemistry using ion chromatography (IC). It was found that a concentration of 1000 ppm NaNO₂, replaced four times, was effective at protecting corroded carbon steel in the presence of chlorides. Nitrite solutions were no more rapid than sodium hydroxide (NaOH) at extracting chlorides from marine steel at equal concentrations and were considerably slower than 2% NaOH. IC analyses indicated that NO₂ does not easily oxidize to NO₃ under normal conditions, but does so readily when a polarizing current is applied, making nitrites unsuitable for electrolytic reduction treatments. Sodium nitrite does show promise as a storage solution prior to desalination of marine metals or after desalination to prevent flash corrosion during rinsing baths.     

The effects of low oxygen atmospheres on the powderpost beetle,lyctus brunneus (stephens)

Abstract

The effect of low oxygen atmospheres on all life stages of the powderpost beetle, Lyctus brunneus (Stephens), was investigated. Artificial diet blocks infested with immature stages of Lyctus brunneus were exposed to a low oxygen atmosphere (0·4% oxygen, balance nitrogen) at 30°C and 70% RH for varying lengths of time. Mortality counts for immature stages were based on the relative number of adult beetles emerging from the treated and untreated diet blocks. One hundred percent mortality was observed for eggs, larvae and pupae exposed to low oxygen atmospheres for six, eight and 12 days, respectively. Adult beetles similarly exposed to low oxygen atmospheres all died within three days.     

Altération et nettoyage de pièces en argent doré

Abstract

By studying the mechanism of sulphation of silver-gilt objects in relation to the method used for gilding, its thickness and its appearance, it has been possible to develop a procedure for electrolytic treatment. The two-step treatment is carried out in a buffered solution of sodium nitrate and comprises cathodic reduction of the silver-based corrosion products followed by anodic dissolution of the reduced silver. The behaviour of the different materials is described, as well as certain limiting factors.     

THE CONSERVATION AND TECHNIQUE OF SILVER BANGLES DISCOVERED AT ROJDI,INDIA

Abstract

The treatment of two silver bangles found at Rojdi and dated c. 2000 b.c. is described. The bangles were separated by removing the hard incrustations with a 20% sodium hexametaphosphate solution and 15% acetic acid. Silver chloride was removed with a 25% solution of 0.88 ammonia and a 20% aqueous solution of ammonium thiosulphate.

Silver sulphide was removed in a 20% formic acid bath. Polyvinyl acetate was used for consolidation, and a coating of polymethyl methacrylate was applied. The silver was found to contain copper and lead. The causes of embrittlement and the manufacturing technique are discussed.     

Evaluation of disinfection techniques for the conservation of polychrome sculpture in Iberian museums

Abstract

Insect infestation is a serious problem in museum collections in Spain and Latin America. This paper investigates the efficacy of modified atmospheres as an anoxant for museum pests, using wooden objects including polychrome sculptures infested by Cerambycidae and Anobiidae species. Insects of long life cycle have been found to be very resistant to carbon dioxide atmospheres. However, inert gases such as argon and nitrogen used in plastic barrier bags effectively eliminated insects in all stages of development. No chemical alteration was observed in the treated materials, including polychromy. These treatments are in progress in a project for biodeterioration control in countries with both tropical or subtropical and Mediterranean climates.     

Cellulose degradation in the Vasa: The role of acids and rust

Abstract

The oak timbers of the Swedish warship Vasa are deteriorating. High amounts of oxalic acid have been found along with a low pH and low molecular weight cellulose deep in the wood timbers. The iron-rich surface wood differs from the interior wood in that it displays higher pH and cellulose with higher molecular weight. The objective of this study was to determine why there is a difference in cellulose degradation, pH, and oxalic acid amount between the surface region and the interior of the Vasa timbers. Analysis of cellulose weight average molecular weight by size exclusion chromatography was performed, as well as quantification of oxalic acid and iron by high-performance anion exchange chromatography and atomic emission spectroscopy, respectively. It was found that a decrease in iron content coincides with an increase in oxalic acid concentration and a drop in pH at a certain depth from the wood surface. When iron-rich surface wood samples from the Vasa were mixed with an aqueous solution of oxalic acid, a fast increase of pH over time was observed. Neither interior wood poor in iron nor the fresh oak reference showed the same neutralizing effect during the time of measurement. This indicates that the presence of iron (rust) causes a neutralization of the wood, through the formation of iron(III) oxalato complexes, thus protecting the wood from oxalic acid hydrolysis. This effect was not observed to the same extent for other acids observed in Vasa wood (sulfuric, formic, glycolic, and acetic acids).     

Optimisation d'un traitement de dechloruration d'objets ferreux par plasmad'hydrogene

Abstract

The method of removing chlorides from archaeological iron objects using hydrogen plasma at low pressure has been studied and improved. To carry out the initial experiments and to limit the use of ancient material, synthetic samples were made from iron powder and corrosion products consisting mainly of akaganeite. The time and the temperature required for the complete removal of the chlorides were determined. It was also possible to demonstrate that magnetite, and iron above 400°C, are the final reaction products of the reduction of akaganeite.     

Influence of crucial parameters on the dechlorination treatments of ferrous objects from seawater

Abstract

This article compares chemical dechlorination treatments (immersion in sodium hydroxide or alkaline sulphite) and electrochemical treatments of iron bars from the Gallo-Roman period excavated from a marine environment. Some important parameters, such as storage before treatment, temperature, solution composition, and drying after treatment, were varied during the study to assess their influence on the chloride extraction process. The kinetics of these treatments depend mainly on chloride diffusion through the corrosion layers. The kinetics are promoted by high temperatures and, in the case of electrolysis, by the electric field effect. The reduction of corrosion products during electrolysis occurs only for objects previously stored in air. In fact, the manner in which the objects are stored before treatment is critical in the dechlorination processes. The sooner the objects are treated after excavation (with water storage), the better the removal of chloride ions, in both chemical immersion and electrolysis treatments. But if the object is stored in air, material losses occur, and only electrolysis results in complete extraction of the chlorides. These differences are due to modifications in the corrosion products during storage. Drying after treatment also has a significant impact on the composition of the corrosion layers. If the objects are dried too quickly, Fe(OH)₂ oxidizes into FeOOH, which thus forms a layer with low cohesion.     

The Freer Gallery Laboratory for Technical Studies in Oriental Art and Archaeology

Abstract

A simple, low cost alternative to X-ray diffraction for the identification of corrosion products on marine iron artifacts is based on the differential solubility of the minerals in pure acetyl acetone and on the color of the product formed.