Wooden Artworks Research Articles

Halloysite Nanotubes Loaded with Calcium Hydroxide: Alkaline Fillers for the Deacidification of Waterlogged Archeological Woods.

A novel green protocol for the deacidifying consolidation of waterlogged archaeological woods through aqueous dispersions of polyethylene glycol (PEG) 1500 and halloysite nanotubes containing calcium hydroxide has been designed. First, we prepared functionalized halloysite nanotubes filled with Ca(OH)2 in their lumen. The controlled and sustained release of Ca(OH)2 from the halloysite lumen extended its neutralization action over time, allowing the development of a long-term deacidification of the wood samples. A preliminary thermomechanical characterization of clay/polymer nanocomposites allows us to determine the experimental conditions to maximize the consolidation efficiency of the wood samples. The penetration of the halloysite-Ca(OH)2/PEG composite within the wooden pores conferred the robustness of the archaeological woods based on the clay/polymer composition of the consolidant mixture. Compared to the archeological woods treated with pure PEG 1500, the addition of modified nanotubes in the consolidant induced a remarkable improvement in the mechanical performance in terms of flexural strength and rigidity. The pH measurements of the treated woods showed that the halloysite-Ca(OH)2 are effective alkaline fillers. Accordingly, the modified nanotubes provided a long-term protection for lignin present in the woods that are exposed to artificial aging under acidic atmosphere. The attained knowledge shows that an easy and green protocol for the long-term preservation of wooden artworks can be achieved by the combination of PEG polymers and alkaline tubular nanostructures obtained through the confinement of Ca(OH)2 within the halloysite cavity.

Evaluation of fungal community involved in the bioderioration process of wooden artworks and canvases in Montefeltro area (Marche, Italy)

Microbiological monitoring represents one of the most useful methods to assess potential risks related to the integrity of cultural heritage. The objective of this work was to evaluate the fungal community prevalent in 64 different artworks of Montefeltro area (Marche, central Italy). A total of 293 swabs were collected and, among these, 2.3% resulted negative to cultural method, while 87.7% were positive for the presence of filamentous fungi, yeasts and Actinomycetes. Totally, 11 genera and 12 different species were recovered from Sabouraud Dextrose Agar (SDA), Czapek Dox Agar (CDA), Malt Extract Agar (MEA), including 73 strains of Mycelia sterilia. Penicillium spp. was isolated mostly from canvases (28.8%), while Aspergillus spp. was most present in wooden artworks (25.3%). SDA was the best performing medium with 57.1% of isolations, followed by CDA and MEA with percentages of 24.8 and 18.1% respectively.This study could be useful to better understand the microorganism-related phenomena in cultural heritage of Marche region, identifying the potential risks and defining preventive protecting such as climate control, frequent cleaning and environmental monitoring.

Femtosecond and nanosecond laser decontaminations of biocidal-loaded wooden artworks

Until the end of the 1980s, many wooden artworks underwent surface treatment by liquid preservatives, e.g., Hylotox-59. DDT (dichlorodiphenyltrichloroethane) crystal structures are formed on the wooden surfaces by the “blooming” of chlorine compounds by time. In addition to an aesthetic disturbance, it is assumed that DDT represents a health risk. Therefore, the removal of DDT crystals from the surfaces is requested. Contaminated wood with natural biocide ageing, gilded and wood carved elements, and wooden samples with paint layers were provided by the Schlossmuseum Sondershausen, Germany. Laser cleaning on selected surface areas on the objects was done by means of femtosecond and nanosecond laser pulses. For the same object, cleaning results using 30-fs laser pulses at 800-nm wavelength are compared to findings utilizing 10-ns laser pulses at 1064-nm wavelength. Before and after laser treatment, chlorine measurements at the same surface position were done by X-ray fluorescence analysis (XRF) as an indicator for the presence of DDT. In this way, pointwise chlorine depletion rates can be obtained for the different pulse duration regimes and wavelengths. In addition, the object surfaces were examined using optical microscopy and multi-spectral imaging analysis.

Nanocomposites based on esterified colophony and halloysite clay nanotubes as consolidants for waterlogged archaeological woods

We have designed an innovative protocol for the consolidation of waterlogged archaeological woods by using acetone mixtures of halloysite clay nanotubes and a chemically modified colophony (Rosin). Firstly, we have investigated the thermal properties of HNTs/Rosin nanocomposites, which have been prepared by means of the casting method from acetone. The HNTs content have been systematically changed in order to study the influence of the inorganic filler on the thermal stability and glass transition process of Rosin. We have observed that the thermal properties of the hybrids are affected by the specific HNTs/Rosin interactions. Then, acetone dispersions of HNTs/Rosin composites at variable filler content have been employed as consolidants for waterlogged archaeological woods. The quantitative analysis of the thermogravimetric curves have provided the amount of consolidants entrapped into the wood structure. These results have been successfully correlated to the consolidation efficiencies estimated from the analysis of the wood shrinkage volume upon drying. The attained knowledge represents the basic step to develop a green protocol for the long term protection of wooden art-works.

Photocurable resin/microcrystalline cellulose composites for wood protection: Physical-mechanical characterization

Abstract Photocurable composites based on a UV-light curable methacrylic-siloxane resin formulation and various concentrations (5 ÷ 20 wt%) of microcrystalline cellulose powder (MCC) were prepared and characterized to assess their suitability as protective coatings for wooden artworks. Dynamic mechanical thermal analysis highlighted that MCC promoted an enhancement of both storage and loss moduli and a decrease of the thermal expansion coefficient. Interestingly, the flexure elastic modulus and the flexure maximum stress of the neat photoresin increased upon the filler addition without any embrittling effect. An increment of hydrophobicity (contact angle), surface hardness (Shore D and pencil scratch tests) of the neat UV-light cured matrix even at the lowest filler loading was observed. These promising results suggest that the photo-curable microcomposites could be able to recover the mechanical and physical properties of damaged wood and replace the traditional resins soluble in toxic solvents utilized in this kind of restoration works.

Microcrystalline cellulose filled composites for wooden artwork consolidation: Application and physic-mechanical characterization

Abstract Two types of historical wood (18th century) ( Juglans regia and Abies alba ) presenting different degradation conditions were consolidated through acetone solutions of microcomposites consisting of a commercial polymer (Paraloid® B72) often used for wood consolidation and two different amounts (5 and 30 wt%) of microcrystalline cellulose (MCC). As a comparison, the same tests were also performed on modern samples of the same types of wood in a well preserved state. Rheological and mass variation measurements evidenced that the introduction of microfiller did not affect the viscosity and the water sorption of the neat resin to a significant extent. Moreover, mercury intrusion porosimetry highlighted how MCC filled composites were able to decrease the pore radius of treated wood samples, reaching values close to those of modern intact wood. Remarkably, the presence of MCC within Paraloid led to a positive enhancement of the stiffness and the flexural strength of treated damaged wood in both quasi-static and impact conditions, with the increase of the flexural modulus, the maximum stress and the rise of both initial and total impact absorbed energies. Additionally, an increase of the radial and tangential surface hardness due to the treatment with MCC filled composites was observed.

Computed Tomography with X-rays and Fast Neutrons for Restoration of Wooden Artwork

The objects of this investigation were sculptures taken from a ca. three hundred years old baroque epitaph of a church in Tönning, a town in Northern Germany. Around 1900 it was found in a disastrous state heavily damaged by wood-worm. At that time, the whole artwork was treated with the tar extract carbolineum as a remedy. Nowadays, this substance has been identified as carcinogenic, and its presence can be perceived by its stench and visually at certain spots on the surface where it has penetrated the covering paint.A gold-painted sculpture of a massive wooden skull was interrogated with X-rays and fast neutrons to investigate the internal distribution of the carbolineum. The X-ray tomography, with its excellent spatial resolution revealed galleries left over from the worm infestation in the outer areas and cracks in the central region. The golden color coating appeared as a thick and dense layer. In comparison the tomography with fast neutrons, though being of lower resolution and yet unresolved artefacts revealed sections of slightly different densities in the bulk of the wood. These differences we attribute to the differences in the distribution of the impregnant in the wood, visible due to its higher hydrogen content making it less transparent for neutrons.

X-ray tomography of large wooden artworks: the case study of "Doppio corpo" by Pietro Piffetti

X-ray computed tomography (CT) is now used in the cultural heritage field because it is non-invasive and it can give a large amount of information on the inner structure of the object under study. Until recently mainly medical CT scanners or micro-CT setups have been used, limiting the analysis to relatively small artworks or requiring multiple acquisition and difficult image-joining for objects larger than detector dimensions. To overcome the limitations of ordinary CT devices, a facility for the X-ray tomography of large size artefacts has recently been designed and installed in a protected area of the Fondazione Centro Conservazione e Restauro "La Venaria Reale", a Centre for Preservation and Restoration. This facility, based on a X-ray source, a linear X-ray detector and a high precision mechanical system, has been and will be used to gather information on materials, manufacturing techniques and conservative conditions of artworks undergoing the restoration process. In this paper the results of the tomography of the first analyzed large artistic object are presented, giving an idea of the wealth of information obtained from the CT scan. The presented artwork is the writing cabinet called "doppio corpo", a masterpiece of furniture more than 3 m high, inlaid for Savoy Residences by Pietro Piffetti, the most famous cabinet-maker in Piedmont in the XVIII century. The artwork is now housed in the Quirinale Palace, the official residence of the Italian President in Rome. The CT analysis permitted us to obtain valuable information about the conservative conditions, the presence of previous interventions, the distribution of various materials and the dimensions and arrangement of several wooden pieces, thus allowing for interesting hypotheses about the building technique of this masterpiece.

Terahertz time-domain imaging of hidden defects in wooden artworks: application to a Russian icon painting

We use terahertz time-domain imaging and time-of-flight tomography to examine subsurface defects in an early-19th-century Russian icon painting. In the transmission geometry, we distinguish between native wood and higher-absorption knotted wood. In reflection, we identify a void in the wood filled with foreign filler material. By using time-of-flight tomographic analysis, we ascertain the depth of burial of the defects. This information helps us to identify the cause of surface faults in the painting, thus allowing the conservators to choose an adequate restoration strategy.

Microwaves as a Remedial Treatment of Wood

A pilot experiment of microwave treatment was carried out on an Art Nouveau residential building erected at the beginning of the 20th century in Valencia, Spain. The timber structure was affected by a combined damage caused by Anobium punctatum (common furniture beetle or common house borer) and Kalotermes flavicollis (yellownecked dry-wood termite). After performing an exhaustive preliminary study on the building and analyzing the different alternatives of wood treatment, it was decided to use a microwave machine especially designed to eliminate this type of wood boring insects.This machine generates microwaves, a type of electromagnetic radiation, with a frequency of 2.45 GHz. This circumstance makes it possible to produce a high-frequency alternating electric field that causes the rotation of the molecular dipoles of water. Because of this continuous rotation the temperature of the water rises considerably.By heating up the humidity inside a living being, as in the case of xylophagous insects, an artificial fever in the body is generated, and since the animal is not capable of tolerating this temperature, it dies.In order to eliminate xylophagous insects, the wood moisture content (usually between 10% and 12%) and the presence of water in wood boring insects (around 90%) must be taken into account. Due to the greater content of humidity the increase of the temperature is higher and quicker in insects than wood.After having studied and experimented with different combination of power and time of exposition to the microwaves, this machine was found capable of eliminating any type of insect that may live inside the timber without harming the wood itself.Prior to this pilot intervention, several research works were carried out with the same microwave machine, both on structural timber and wooden works of art. In all these studies it was observed that no damage was caused either to the wood or to the finish of the works of art including pigments, polishes, stains etc. On the other hand, 100% efficacy was achieved in the elimination of xylophagous insects.This article describes the design, experimentation and perfecting process of this microwave machine and its pilot application on structural timber in an Art Nouveau residential building. As an example of method, the intervention followed the main steps of diagnosis and treatment testing including the analysis of several options of intensity and time that led to the positive final results obtained.

Decontamination and “deconsolidation” of historical wood preservatives and wood consolidants in cultural heritage

Abstract In the past, wood artifacts were treated with a variety of wood preservatives formulated on the basis of inorganic and organic biocides. Most of these biocides have a high human toxic potential and pollute the environment. Some of them even cause damage to the objects they were meant to preserve. This poses a considerable challenge to the handling, exhibition, storage and restoration of such wooden works of art. In addition, biocide-containing structural wood members in historic buildings pollute the indoor-air, and represent a permanent health risk. Wood artifacts previously damaged by organisms and subsequently preserved and consolidated with mixtures of vegetable oils and natural resins now show characteristics of renewed deterioration. An important condition for the re-treatment of such objects is the exact detection of the substances originally utilized for their conservation. Non-destructive and in situ -measurements have priority among the listed analytical methods. The various decontamination procedures currently used are classified in regard to their mode of operation. Preferred methods include mechanical cleaning, thermo desorption, washing with water and detoxicants, and leaching as well as extraction with liquid or supercritical carbon dioxide. The masking with various sealers to prevent biocide evaporation into the indoor-air is limited to application to structural wood members. Leaching of degraded natural consolidants in wood artifacts is currently undertaken in a testing plant.

Laser cleaning of 19th century Congo rattan mats

There is a growing interest by art conservators for laser cleaning of organic materials, such as wooden artworks, paper and textiles, since traditional cleaning with solvents can be a source of further decay and mechanical cleaning may be too abrasive for sensitive fibers. In this work we present a successful laser cleaning approach for 19th century rattan mats from the Brooklyn Museum collection of African Art, now part of the study collection at the Conservation Center in New York. Tests were carried out using the fundamental (1064nm) and second harmonic (532nm) wavelength of a Q-switched Nd:YAG laser to measure threshold values both for surface damage and color changes for different types of rattan samples. The irradiated substrates were investigated by optical microscopy, scanning electron microscopy and by UV–vis spectroscopy in order to determine the efficiency of laser cleaning and to assess possible deterioration effects that may have occurred as a result of laser irradiation. The study showed that by using the laser emission at 532nm, a wavelength for which photon energy is below the bond dissociation level of the main cellulosic compounds and the water absorption is negligible, it is possible to select a range of laser fluences to remove the black dust layer without damaging the rattan material.

IDENTIFICATION OF WOOD AND WOOD - BORING INSECTS OF THE ICONS OF BERATI`S MIDDLE - AGE MUSEUM IN ALBANIA: FIRST STEPS OF THEIR RESTORATION AND CONSERVATION

UDK 674.5:595.7(496.5 Berati)
 There are about 350 icons at the deposit of the Middle Age Museum of Berati, among 4500 items of very precious wooden artwork heritage, all over Albania, Actually four of these icons are under restoration process and our first scientific collaboration in this process consisted in identification of wood and wood-boring insects.
 The technique used for the anatomic study of the icons wood was the resin inclusion. After chemical treating of small samples in resin (butyl based) and their thermal treating in thermostat (temperature 60ºC for 12 hours), anatomic sections were prepared by microtome. The microscope observations showed that three icons belong to Juglans regia L. (very typical specie of the forests of that area) and only one belongs to Populus sp., probably Populus alba L., because it is the only one specie naturally grown in Osumi valley in the south of Albania.
 Accurate observations and measurements have been done for the inspection of wood deterioration, which showed considerable fungi decay and insect damages, especially from Anobium punctatum. The method of vacuum was used for insect disinfection of icons. The process of wood identification is going on for the other icons in the restoration process.

An advanced church heating system favourable to artworks: A contribution to European standardisation

Abstract The European project Friendly-Heating (FH) : comfortable to people and compatible with conservation of artworks preserved in churches addressed the problems caused by the continuous or intermittent heating of historic churches, which disturbs the microclimatic conditions to which the building and the artworks preserved inside have acclimatised. As thermal comfort and the preservation of artworks often conflict with each other, a balance between the two needs is necessary. The proposed heating strategy is to provide a small amount of heat directly to people in the pew area while leaving the conditions in the church, as a whole, undisturbed. This novel heating system is based on some low-temperature radiant emitters mounted in a pew to provide a desirable distribution of heat to the feet, legs and hands of people occupying it. Due to little heat dispersion, this novel system not only significantly reduces the risk of mechanical stress in wooden artworks and panel or canvas paintings, fresco soiling and cyclic dissolution-recrystallization of soluble salts in the masonry, but is energy-efficient. The detailed environmental monitoring was conducted in the church of Santa Maria Maddalena in Rocca Pietore, Italy over a 3-year period to verify the performance of the novel heating system in comparison to the warm-air system that was active earlier in the church. The methodology and results of this comprehensive and multidisciplinary study were included in three draft standards of the European Committee for Standardisation intended for use in the study and control of environments of cultural heritage objects.