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.     

Climatically Induced Degradation Processes in Conserved Archaeological Wood Studied by Time-lapse Photography

ABSTRACT

Samples of conserved archaeological wood of different ages, origins, and conservation histories were aged in a climate chamber for seven months, while the humidity alternated between 30% RH for 12 hours and 80% RH for 12 hours at a constant temperature of 30°C. Photographs were taken once every hour, which enabled the creation of a time-lapse movie. Some samples degraded visibly, whereas others were unaffected. Most of the samples were robust and would be able to survive well even in a very poor museum climate. Among the sensitive samples, three types of degradation were identified, namely disintegration, pyrite oxidation, and efflorescence of white crystals. Disintegration was ascribed to dimensional changes caused by the RH alternations in very fragile wood. The white efflorescence was interpreted as the recrystallization of an alum-associated substance, possibly mercallite (KHSO₄). The pyrite oxidation was observed as the efflorescence of a thick yellow, grey, and green powder. Characterization of selected samples was performed using X-ray fluorescence spectrometry, X-ray diffraction spectrometry, scanning electron microscopy with energy dispersive X-ray spectroscopy, inductively coupled plasma – optical emission spectroscopy, Fourier transform infrared spectroscopy, ionic conductivity – liquid chromatography, and pyrolysis-gas chromatography-mass spectrometry with in situ silylation using hexamethyldisilazane.     

Oxygen concentration and mobility in conserved archaeological wood

Probes for measuring oxygen concentration were installed inside large samples of conserved wood from archaeological shipwrecks to record oxygen profiles as a function of depth under the wood surface. The concentration of oxygen was lower inside the wood than outside indicating that the supply of oxygen is limited and that oxygen is consumed within the material. This was confirmed by oxygen consumption rates averaging 1.3 ± 0.42?µg O₂/g wood/day. The diffusion properties were estimated by placing the wood samples in a nitrogen atmosphere and measuring nitrogen breakthrough time to the oxygen probes at different depths. A high level of variation was observed between the breakthrough times measured at different depths of the samples. This indicated that the access of oxygen is irregular, possibly due to wood heterogeneity and uneven distribution of conservation agent. By recording oxygen concentrations inside archaeological wood under stable environmental conditions, it was shown that oxygen concentration profiles are almost constant over a time span of seven years. This indicates that oxygen consumption, and thus oxidative degradation, is constant for an extended period of time. It also shows that the oxygen concentration inside conserved archaeological wood is a steady state value controlled by the local balance between oxygen supply and oxygen consumption.     

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.     

Decay of softwood in archaeological wooden artifacts

Hardwoods and softwoods were used side by side throughout Egyptian history, and importing softwoods that had an attractive color and texture was common. Over the decades, artifacts based on hardwoods and softwoods underwent deterioration phenomena, sometimes reaching either a level of brittleness or turning into a wood powder that may easily crumble. These levels of decay/degradation are often difficult to handle in terms of conservation treatments. To study or identify the reasons for decay has always been a point of interest for conservation purposes, but to assess decay and choose an appropriate treatment according to the state of preservation for the sake of keeping an artifact intact has become a subject of major importance. It is difficult at times to understand the deterioration process, because hardwoods and softwoods are different in structure, properties, and chemical composition. For this preliminary study, decayed samples from three commonly used softwood types, cypress (Cupressus sp.), cedar (Cedrus sp.), and pine (Pinus sp.), were identified and chosen. Scanning electron microscopy (SEM) of the samples indicated the degree of decay. Decayed and non-aged samples of the same wood type were analyzed using Fourier transform infrared spectroscopy (FTIR), and all the major carbohydrate and lignin bands were recorded. The strong hydrogen bonded (O–H) stretching absorption associated with water linked by hydrogen bonds to the –OH groups of cellulose and hemicelluloses in all decayed samples increased with decay. The brown powdery, fragile samples that had been evidently affected by microbial decay had a higher amount of lignin. The lignin/carbohydrate ratio was calculated and results compared. The increase of either lignin percentage or extractives in some of the samples had caused a darkening of color in both cypress and cedar samples, but the pine sample did not have the same texture and appearance. In cases where the lignin percentage decreased the samples had changed to a slightly lighter color. FTIR results explained the decay phenomena observed in SEM micrographs and helped assess wood decay and also confirmed results that had been previously obtained while applying traditional chemical analysis on wood.     

Mechanical strength studies on degraded waterlogged wood treated with sugars

This study aims to measure the mechanical strength of chemically degraded wood samples and compare the values obtained with fresh wood and degraded wood treated with sugars. The mechanical strength of chemically degraded waterlogged wood samples was determined using a three-point bending system to generate load-deflection curves and subsequently calculate the modulus of elasticity and load to failure longitudinally. The values obtained allow us to compare the mechanical properties of white birch wood samples that were air dried after treatment with 60% w/v solutions of sucrose, trehalose, or sucralose. In addition, the same parameters were measured for fresh white birch wood samples and chemically degraded samples that were allowed to air dry without treatment. Fresh white birch was found to have a longitudinal modulus of elasticity of 11.5?GPa whereas this value decreased by 70% when the wood was degraded. Treatment with sugars increased the measured values of modulus of elasticity up to 36.9?GPa, a substantially higher value than for fresh wood. These data indicate that non-reducing sugars could be useful alternatives to polyethylene glycol for the conservation of waterlogged archaeological wood.     

Conservation of chemically degraded waterlogged wood with sugars

The effectiveness of two non-reducing sugars, both analogues of sucrose, to conserve degraded waterlogged wood was examined. The two sugars examined are trehalose and sucralose, both stable and relatively unreactive. The ability of these sugars to conserve a series of degraded tongue depressors was measured by determining the anti-shrink efficiency of each at various concentrations and comparing them to sucrose. The findings of this study indicate that both sucralose and trehalose may be effective conservation treatments for waterlogged archaeological wood and that at moderate concentrations the performance of both is comparable to sucrose. However, sucralose has a lower solubility, and concentrations higher than 60% w/v were not examined, whereas concentrations of up to 100% w/v of trehalose were studied. At these higher concentrations trehalose performed as well, if not better than sucrose, although there were crystalline deposits on the wood surface at these higher concentrations. With modifications and careful control, both of these sugars may be suitable conservation alternatives to sucrose due to their long-term stability and resistance to hydrolysis.     

Technologies for Wood Preservation in Historic Preservation

Because of the abundant forests of the world, wood is one of the most common materials found in historic buildings. Wood is relatively easy to fabricate into beams, columns, and roof systems using simple hand tools. However, because of its biological origin, wood is one of the most complex constructions materials. It is produced by thousands of different species of trees, and each type of wood has unique properties. Wood has an affinity for moisture and this can lead to biological deterioration caused by insects and decay fungi. This chapter presents information on understanding and preventing the mechanisms of wood deterioration in historic buildings. The chapter includes a discussion of wood preservation and technology, including wood finishes and wood preservative treatments, diffusible preservatives, and naturally durable wood species. A brief discussion about the repair of deteriorated timbers in buildings is also included.     

Natural polymers as alternative consolidants for the preservation of waterlogged archaeological wood

In recent years, there has been increased interest in examining alternative polymers for the conservation of archaeological artefacts, particularly waterlogged timbers, providing better, renewable, greener alternatives to poly(ethylene glycol) (PEG). The degradation of PEG consolidants in the timbers of the sixteenth century warship Mary Rose has been examined and the rheological and thermal properties of PEG have been compared with its monomethyl and dimethyl ethers and several polysaccharide consolidants (chitosan, guar, and 2-hydroxyethyl cellulose) in order to evaluate their potential as alternative consolidants for the conservation of waterlogged wooden artefacts. Additionally, the effect of the polymers on the archaeological wood was characterised by thermogravimetric analysis and solid-state nuclear magnetic resonance spectroscopy. The results suggest that the future of conservation technologies lies with polysaccharide consolidant materials, which show enhanced compatibility with wooden artefacts with no detectable side effects while also being cheap, with extremely low toxicity, renewable, and sustainably resourced.     

Conservation Heating 24 Years On

ABSTRACT

Control of relative humidity (RH) for collections care is challenging in U.K. historic houses because they are often highly ventilated with poor heat retention, a porous building fabric and naturally tend to high (60–80%) RH if unheated. The significance of the building means that large-scale modifications and installation of air handling systems may be unfeasible and undesirable for the conservation of the building. In the late 1980s the National Trust, for English, Wales and Northern Ireland, investigated conservation heating as an RH control method that works with the natural environment of historic buildings, mimicking historic heating and requiring only modification of existing heating services or a light touch installation of new heating systems. The National Trust adopted conservation heating as its preferred method for environmental control in historic buildings from the 1990s. This method was presented at the IIC 1994 Ottawa congress on preventive conservation. Conservation heating has since been adopted by many historic house management organisations, particularly across north-west Europe, where it is well suited to the climate. This paper reviews conservation heating developments implemented by the National Trust since 1994, in response to a changing external context, new knowledge and developments in operational practice.     

Changing research trends in the field of archaeological wood at the Conservation Department,Faculty of Archaeology,Cairo University

Abstract

Since 1980, much research in the field of treatment and conservation of archaeological wood has been carried out at the Conservation Department, Faculty of Archaeology, Cairo University. Materials and methods used in conservation have been changing gradually over the years worldwide. It was necessary to study critically previous masters and doctoral dissertations on Egyptian archaeological and historic wood, all written in Arabic. This review of them includes a brief history of the Conservation Department at Cairo University and five main focal points of past research: types of wood used throughout Egyptian history, assessment of wood decay, wood properties and composition, treatment and conservation of decorated wood, and the evaluation of chemicals and polymers used in the treatment of archaeological wood and composite objects containing wood.     

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.     

Chemical bleaching of wood: an investigation into the bleaching of mahogany,walnut, rosewood,padauk, and purpleheart

This paper investigates chemical bleaching of wood to make species-specific practical recommendations for colour adjustment of veneer in furniture conservation. In more detail, chemical bleaching of Honduras mahogany (Swietenia macrophylla), European walnut (Juglans regia), Rio rosewood (Dalbergia nigra), padauk (Pterocarpus spp.), and purpleheart (Peltogyne spp.) is investigated using 11 different bleach solutions. Both oxidative (e.g. hydrogen peroxide and potassium permanganate) and reductive (e.g. oxalic acid and sodium bisulphite) solutions were used. The results show that the wood species react differently with the investigated bleach solutions. It can also be noted that not all investigated solutions were suitable for all wood species. Based on the results, wood species-specific bleach solutions are recommended.     

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.     

The wharf-borer Nacerdes melanura L., a threat to stored archaeological timbers

Abstract

A survey of stored waterlogged archaeological timbers from the Mary Rose revealed that 2% of these timbers were infested by larvae of the wharf-borer beetle, Nacerdes melanura L. Timber species attacked included oak, poplar and pine, with moisture contents ranging between 130 and 670%. In addition, scanning electron microscope studies demonstrated that wood tunnelled by the larvae was microbially decayed. The larvae and their life-cycle were studied and emerging adults were observed penetrating the 500 gauge polyethylene used to wrap timbers. Studies showed that 60 Nylon/100I Surlyn, 70 Nylon/125I Surlyn, T 1–19v, T 1–25x and Camvac were more suitable wrapping materials.     

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.     

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).     

Long-term changes in climate and insect damage in historic houses

Abstract

Insect pests are an important source of concern in historic houses as the larval stages in particular can feed on a variety of important heritage materials, causing significant and sometimes irreparable damage to collections. Damage to wood and textiles is a special problem. The lifecycles of insects are sensitive to climate and require relatively warm conditions. There has been a significant increase in the presence of insect pests within historic houses in the early twenty-first century. The reasons may include: warmer winters, widespread use of natural fibres, less potent insecticides, and occupation of new niches indoors. The interior climate, especially increasing warmth, offers the potential for greater insect growth and survivability. Modelling changes in the temperature and humidity within the Cartoon Gallery at Knole, southern England, for the period 1770–2100 suggests a dramatic increase in favourable temperature conditions through the current century.     

An investigation of the use of cellulose-based materials to gap-fill wooden objects†

The conservation of wooden objects is complicated by their response to changes in their environment. In particular, filling voids in wooden objects can be difficult when their dimensions might be expected to alter over time. A short survey of conservators showed that a wide variety of materials have been, and are being used for this purpose. Following conservation work undertaken on a wooden coffin, the author wished to investigate the properties of cellulosic materials and their suitability in the conservation of wooden objects. This paper shares the results of experiments that were conducted to determine the way in which hydroxypropyl cellulose (HPC) and paper pulp fills respond in various conditions, as compared to other fill materials used by conservators. The compatibility of the HPC and paper pulp fills with wood is satisfactory enough to be able to recommend their use in the conservation of wooden artefacts, but ideally further experiments would be carried out, and on a wider variety of fill materials.