Problems of adhesion between support and ground layers in polychrome wooden sculptures in Guatemala

Abstract

Bibliographical research and scientific analysis of samples obtained from five polychrome wooden sculptures of the colonial tradition in Guatemala were used to study the techniques and the materials used. The methodology involved qualitative analysis of the samples and microscopic examination of cross-sections. Scanning electron microscopy (SEM) was used to identify pigments and to ascertain the composition of the gilding. It was hypothesized that the deterioration of the sculptures, particularly the separation of the ground layers from the wooden support, was due to the action of secondary products of Cedrela odorata L. The loss of adhesion of the animal glue used in the preparation may be partly related to the precipitation of the protein of the gelatin due to the action of the tannins present in the wood.     

A New Cradle Model

Abstract

There is evidence in the literature that in India wood was used for making sculptures from very early times. Owing to the destructive climate, however, only wooden objects dating from the 7th century are available today, while polychromed wooden sculptures of the period before the 16th century are unobtainable. Sculptures were produced either by carving from one solid block or by building it up from small pieces. The main types of decorating were painting, inlay work or lac work. Painting was done sometimes without, but mostly with surface preparation. For this a thin layer of a ground was used. Sometimes a layer of cloth and then paper was used before applying the gesso. Pigments in common use were malachite, terre-verte, red ochre, red lead, lac dye, yellow ochre, chrome yellow, ultramarine, kaolin, and chalk. A gold effect was often produced by applying shellac varnish over shining silvery tin paint or foil. Lac work was produced by painting with lac solution or by turnery.     

THE CONSERVATION AND TECHNIQUE OF THE HERLIN ALTARPIECE (1466)

Abstract

The restoration of the Hedin altar in Rothenburg o.d.T., dated 1466, is described. The polychromed sculptures were cleaned and loose paint was fixed. Methods and materials used in the restoration of the paintings, the areas polychromed in various techniques and the brocade reliefs are mentioned. The altar was protected from direct sunlight. The construction of the shrine and the technique of carving are extensively discussed. Sculptures made from one piece of lime wood were hollowed out and closed with a plank. Traces of rough finishing are visible. Shrine and predella were polychromed after a preliminary assembly of the sculptures. The various techniques used in the undisfigured polychromy are described as they are observed with the unaided eye. It can be shown that the working methods were rational. The fabrication of relief brocades and the various patterns used are discussed in detail. The treatment of the various paintings on the wings, the predella and the reverse of the shrine is reported. The question is raised to what extent the painter Herlin can also have been responsible for the polychromy.     

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.     

Preliminary tests for mechanical properties of wooden ‘buttons’ used for attaching auxiliary supports behind panel paintings

Abstract

When wooden supports of panel paintings have been severely altered or damaged and the original cross beams are missing, new cross beams or other types of auxiliary supports are connected to the panel's back-face in order to achieve desired effects including panel strengthening and control of deformations. Some conservation laboratories use small wooden blocks, each glued on the back face of the panel and holding freely the head of a screw connected (often by means of springs) to the auxiliary support; such blocks being called in Italian ‘piedini’ or ‘bottoni’, the English term ‘buttons’ is proposed here. This paper reports research aiming to characterize the mechanical behavior of three types of ‘buttons’ having different geometries and made of various wood types (oak, walnut, lime, beech, and a medium density fiberboard). Short-term mechanical tests (～1 minute duration) were performed with a universal testing machine by axially pulling out the 4 mm diameter steel screw from the button, glued onto a dummy board. Load and deformation were recorded, and the load–deformation curves were analyzed. The results show that the deformability and the load-carrying capacity of the buttons were influenced primarily by the manufacturing geometry and secondarily by the wood density.     

Technique and restoration of three sculptures by Pedro de Mena

Abstract

This paper describes the examination and treatment of three polychrome wooden sculptures by Pedro de Mena, an important seventeenth-century Spanish sculptor. These were three interesting cases, involving not only the usual conservation processes but also special situations such as the recovery of a glass eye, the replacement of missing parts and polychromy with the help of old photographs, and the analysis of a sculpture where the flesh colours varied depending on whether or not they had been exposed to sunlight. Our understanding of polychrome sculpture technique is enriched with new information concerning the blues of the cloaks, coloured glazes, and materials added to the paint to achieve different effects.     

Cross-sections and Chemical Analysis of Paint Samples

Abstract

Consolidation of decayed wooden artifacts can be achieved by impregnation with epoxy prepolymer dissolved in a mixture of toluene and glycidyl ether and subsequent polymerization in situ. The principles of selecting the successful method of application are discussed, and the details of the procedure given. Impregnation with the described solution causes insignificant expansion of the wood in contrast to the action of polyvinyl acetate in alcohol solution.     

Two of a Kind: Shining New Light on Bronze Spiritelli Attributed to Donatello

ABSTRACT

Two Spiritelli attributed to Donatello have been extensively studied from a technical point of view, including X-radiography, alloy analysis, characterization of the core, and visual observations on the interior and exterior of the statues. The results of this technical study reveal how the two statues were cast and document the artist’s technical choices. These new insights offer additional information to address questions regarding their attribution, production context, and conservation history. First, the technical study confirmed that the statues were made by the same workshop and argues against the prior proposal of different attributions for the two figures. Second, the results strongly suggest that the statues have never been separated since they were taken off Luca Della Robbia’s Cantoria. Finally, study of the two Spiritelli offers further evidence of the heterogeneity and ingeniousness of Donatellos bronze artistic production, and contributes to the ongoing debate whether the artist himself was involved in the technical aspects of his sculpture.     

A case study of the conservation of the polychromed wooden choirloft of the seventeenth-century church at Carabuco,Bolivia

Abstract

The restoration of the seventeenth-century adobe church at Carabuco, Bolivia, offers a model of how to conduct the preservation of the Latin American cultural heritage at remote sites. This paper details the conservation of the church's polychromed wooden choirloft, which had previously been restored in 1765-66 after this and other portions of the church collapsed. The choirloft is made oflocally grown eucalyptus wood painted all over with a tempera-based medium. It was executed by a local artist whose style draws on local folk-art traditions while reinterpreting European Renaissance decorative schemes. The choirloft conservation project had two goals: to guarantee its structural integrity and to stabilize the decorative paint layers. These goals were accomplished in a four-month conservation project which formed part of a larger effort to restore the church.     

Light-induced color changes and chemical modification of treated and untreated chestnut wood surface

Abstract

The aim of this work is to study the surface modifications of chestnut (Castanea sativa Mill.) wood by reflectance spectrophotometry and Fourier transform infrared spectroscopy (FTIR) in order to understand the mechanisms that cause changes and to suggest possible solutions to avoid degradation phenomena. The experimental data were statistically treated to evaluate their significance. Concerning the surface protection of wood, starting from the results obtained by testing different commercial products, attention was focused on a novel organic preservative/consolidant product (Linfoil^®) that has attracted great interest in the field of conservation of wooden artifacts. Color monitoring showed that wood surface color undergoes an important variation due to photoirradiation, occurring within the first 24 hours and mainly due to L* decrease and b* increase. Though the protective treatment modifies wood color, nevertheless the product tested seems to protect the wood surface by reducing photoyellowing. FTIR analysis indicated that irradiation caused the degradation of lignin and increased the concentration of the chromophore groups on the wood surface. Changes in the chromaticity coordinates can be linked to the degradation of lignin and to increase of the concentration of carbonyl groups.     

POLYCHROME SCULPTURE IN SWEDEN

Abstract

A survey is given of polychromed sculpture in Sweden. Historical aspects of the care of sculptures are discussed. Many retables have been imported from Lübeck and Antwerp. Polychromed sculptures are often well preserved because there was hardly any iconoclasm in Sweden. Many need treatment however due to various forms of neglect. A special case—the triptych of Kärrbo (c. 1500)—is described in detail from a technical point of view.     

Microwave Treatment for Pest Control: Coleoptera Insects in Wooden Objects

By far the most common species of woodworms perceived to be the main cause of damage to wood, and in particular to wooden art objects, are Anobium punctatum de Geer and Hylotrupes bajulas of Coleoptera family. In search of non-chemical methods for eradicating these wood pests, microwave (MW) heating can be an effective tool to help control the insects in their different life stages (eggs, larvae, and adult). The effect of 2.45?GHz frequency MW exposure on wooden art objects is described and discussed. MW heating time is reported in connection with lethal temperature of the pest and moisture content of the treated wooden object. The treatment was carried out using Microwood 12, especially conceived for portability, easy operation, and control. Microwood 12 consists of a switch mode high-voltage power supply and an industrial continuous wave magnetron connected to a rectangular-shaped horn antenna. The measure of temperature and control of operation is done via a built-in infrared thermometer.     

Method for Stabilization of Leaded Bronzes Affected by Corrosion of Lead

Abstract

To inhibit the corrosion of lead objects and lead in high-lead bronzes, particularly in the presence of organic emanations from wood, paint, etc., and/or high humidity, is a difficult conservation problem. A method to prevent corrosion of lead in copper objects was therefore developed using benzotriazole (BTA). The most appropriate treatment method for the conservation of the objects was to immerse them in neutral BTA solution, for which a 0.5% (w/v) concentration of BTA was enough. For bigger objects, three or four coats of 1.0% solution applied by brushing were equally effective. The method was used successfully for the conservation of some ancient copper coins and bronze sculptures containing high amounts of lead; it can also be used to inhibit corrosion of lead objects.     

Analysis and conservation of modern modeling materials found in Auguste Rodin's sculptures

Prior to the exhibition Portrait-making, Rodin and his models (2009), the Rodin museum wanted to restore two busts of Hanako and Clemenceau. Interestingly, these two sculptures contain pieces of modern modeling materials (MMMs) invented at the end of the nineteenth century as an alternative to clay or waxes. The poor state of conservation of the two portraits made any handling and exhibition impossible. Accordingly, the purpose of this article is twofold: to contribute to technical art history and conservation. Elemental and chemical analyses were done on samples from 12 sculptures (SEM–EDX, FTIR, GC–MS, GC–FID, XRD, synchrotron-based µXRF, µXANES, and µFTIR) aimed at identifying the composition of MMMs used by Rodin on plaster sculptures and establishing hypotheses about the origins of their degradation. This thorough study of their composition and degradation was necessary to implement an appropriate restoration plan. The development of conservation protocols adapted to such materials is rarely documented. Different tests were performed on mock-ups (pH, solubility, adhesion, consolidation, and cleaning). In particular, a protocol based on laser cleaning was developed and successfully applied to remove superficial dust and crusts so that the sculptures regained their original aspect.     

Dimensional Stability and Moisture Properties of Gap-Fillers Based on Wood Powder and Glass Microballoons

ABSTRACT

Conservation of wooden objects exposed outdoors is extremely difficult and complex due to their constant exposure to fluctuating weather conditions and biological degradation. Filling the gaps in such objects requires the use of specific materials that in particular can adapt to changes in wood dimensions in response to humidity variations. Various materials have been used so far for filling voids in wooden artefacts but none of them was entirely suitable. Therefore, the authors have attempted to provide the basic characteristics of the selected commonly used filling materials based on pine wood powder or glass microballoons as fillers and Paraloid® B-72, Klucel® G, or glutin glue as binders, as the first step in research aiming at developing new and more appropriate gap-fillers. Special attention was paid to the dimensional stability of filling materials upon drying and exposure to water vapour and liquid water. The overall results indicate that among the examined fills those consisting of Paraloid® B-72 and glass microballoons revealed best properties as they were relatively dimensionally stable upon drying and exposure to moisture – despite high absorption of water – and were quite easy to finish. Generally, better properties were observed for filling materials containing higher concentrations of adhesives and these materials will be modified in the next step of the research. Since the main drawbacks of the examined gap-fillers were low water resistance, poor dimensional stability upon drying or exposure to water vapour or liquid water, and fragility or friability, future research into their modification will head towards improvement of the above-mentioned properties.     

Climatological analysis in relation to the conservation of a sixteenth-century spanish polychrome wooden ceiling

Abstract

A sixteenth-century Spanish wooden ceiling was installed in the Morning Room of Hearst Castle in the early 1920s. Since that time, the adhesion between the ground/paint layer and its wooden support has weakened considerably. As a first step in designing an effective conservation program, it was necessary to assess the role of the environment in this deterioration process. Air movement patterns, humidity and temperature parameters, air pollutants, and the impact of approximately one million visitors per year on the microclimate were studied over a one-year period. Correlations between the various components of the study were mapped, including CO₂ concentrations vis-à-vis the number of visitors, and humidity and temperature changes in relation to tourists, air circulation patterns and variations in the external climate. As a result of this study, temporary measures were taken to improve the conditions of the immediate environment and proposals were made for more permanent solutions.     

SOME ASPECTS OF THE CONSERVATION OF WORKS OF ART IN BUILDINGS OF NEW CONCRETE

Abstract

This paper deals with the materials used in conservation treatments in the first half of the twentieth century for the preservation and consolidation of wooden art objects from the Saxony region in Germany. The use of such materials must be seen as early attempts to find a conservation treatment for wood. The documentation of conservation treatments provides a reference to the application of oils and oil–resin mixtures. The results from the chemical analysis of samples of historic preservatives from the beginning to the middle of the twentieth century (so-called 'Puckelin') carried out by gas chromatography–mass spectrometry (GC-MS) and Fourier transform infrared (FTIR) analysis confirm the use of tung oil as a drying oil, whereas the use of linseed oil cannot be excluded. Colophony and, probably, amber varnish were used as resinous constituents. There are indications that a conservation material dating from the second half of the twentieth century most likely contained rapeseed oil.     

Relating relative humidity fluctuations to damage in oak panel paintings by a simple experiment

ABSTRACT

Panel paintings are essentially wooden boards painted on one side. Due to the vapor resistance of the paint layer, changing ambient conditions lead to exchange of moisture on only one surface. Subsequently, a non-uniform moisture content profile is formed across the thickness of the board. As a result, differential expansion causes the board to bend in case of no mechanical restriction, or it leads to a build-up of stresses inside the material if restrained. Experiments with oak boards sealed on one side and exposed to a change in the ambient relative humidity (RH) were performed. By scaling, the response of any board with different thickness can be predicted. Since the bending of the board can be described as a linear system behavior, the frequency response can be predicted based on the step response. In combination with critical strains for wood and gesso from the literature, this gives insight into allowable RH fluctuations in terms of frequency and amplitude for different board thicknesses.     

Materials and techniques: Early Buddhist wall paintings and sculptures at Sumda Chun,Ladakh

An assemblage of Buddhist wall paintings and sculptures dating to the twelfth/early thirteenth century are found distributed over the interiors of the temple complex at Sumda Chun, Ladakh. Detailed investigations carried out as part of a conservation project shed light on their antiquity and production technology. The sculptures are constructed with fine mud mortar applied over a wooden armature and affixed to the walls without any support from the ground. In both the sculptures and wall paintings, the paint layer is applied over a thin gypsum ground that functions as a white colourant where unpainted. For the paint layer, azurite, vermilion, and orpiment are the dominant mineral pigments utilized. Minium (red lead) has been used for preparatory drawings and as paint. Highlighting of special areas was achieved using a laminate of tin–lead alloy and gold on relief. Overall the material and techniques employed in the execution of the wall paintings and sculptures are consistent with those reported for other early sites in the region.     

Essai de Reconstitution d’un Procédé de Fabrication des Lames d’Épées Damassées

Abstract

During 1977–78, a conservation project was undertaken by the Federal Government of Canada to preserve the weathered hull of the HD-4, an experimental hydrofoil craft built at the laboratorie of Alexander Graham Bell in Baddeck, Nova Scotia. After achieving a world marine speed record of 70·86 m.p.h. (114·01 km.p.h.) in 1919, the craft was beached on the shore of a salt water lake. Forty years’ exposure to severe weathering caused wood rot, metal corrosion and the disintegration of the canvas covering. Due to the deteriorated condition of the craft and the loss of most of the external structures, complete restoration was not desirable or practical. The aim of the project was therefore, to stabilize the wooden hull, while preserving its weathered appearance.