Showing papers in "Studies in Conservation in 2007"

Natural Dyes: Sources, Tradition, Technology and Science

Abstract: (2007). Natural Dyes: Sources, Tradition, Technology and Science. Studies in Conservation: Vol. 52, No. 4, pp. 318-319.

Analytical Imaging Studies of Cross-Sections of Paintings Affected by Lead Soap Aggregate Formation

Abstract: Lead soap aggregateshave been-found in lead-containing oil paint layers in paintings from the thirteenth to the twentieth century. They severely affect the stability of the paint layers and disturb the surface of the paintings. Paint cross-sectionsfrom five paintings affected by lead soaps were selected to illustrate and investigate this degradation phenomenon with the analytical imaging techniques of Fourier transform infrared spectroscopy, secondary ion mass spectrometry and scanning electron microscopy combined with X-ray analysis. Examples aregiven of lead soapsforming in a mature paint system or, alternatively, in the early drying stage of the oil; lead soapsforming from various types of lead-containing pigments or driers; lead soapsforming in multiple paint layers; and lead-containing crystallization products inside aggregates. The phenomenon of lead soap aggregatesis multifaceted, and one general scenario describing theformation of lead soap aggregatescannot explain all aspects. However, th...

Animal glues: a review of their key properties relevant to conservation

Abstract: Collagen-based animal glues are widely used in the conservation of artefacts, serving as adhesives, binders and consolidants for organic and inorganic materials. With a variety of different animal glues on the market, such as hide and bone glues, fish glues, isinglass and gelatin, their individual properties need to be well understood in order to choose a glue fit for a specific purpose. This paper reviews a wide range of publications on currently available animal glues, with respect to their specific physical, chemical and mechanical properties.

Impact of Indoor Heating on Painted Wood - Monitoring the Altarpiece in the Church of Santa Maria Maddalena in Rocca Pietore, Italy

Abstract: Triangulation laser displacement sensors were applied to the continuous in-situ monitoring of the dimensional response of the wooden altarpiece in the Church of Santa Maria Maddalena in Rocca Pietore, Italy, to variations in indoor temperature and relative humidity (RH) between December 2002 and March 2005. Further, a small inductive sensor was used to monitor the width of a crack in one of the elements. The measurements demonstrated that only the external layer of wood, several millimetres thick, continually absorbs and releases water vapour following external variations in RH. For massive elements, this leads to gradients in the moisture content through the wood, a restraint of the dimensional change and a development of stress, which is the main threat to the integrity of the wood and the decorative layer. Particularly strong RH variations and related high stress levels were produced by the intermittent heating system based on the inflow of warm air. To incorporate requirements for preservatio...

A Novel Method to Determine Oxidation Rates of Heritage Materials in Vitro and in Situ

Abstract: A novel method for measuring oxidation rates of heritage materials is described. The method uses optical oxygen sensors, which allow measurement of the oxygen concentration through the transparent wall of a closed container. Three experimental designs are described: first, using glass containers in which the samples can be followed for extended periods; second, using bags composed of oxygen barrier film that have flexible dimensions suitable for irregularly shaped artefacts; and third, using glass dishes glued to the surface of larger artefacts, allowing measurement of oxygen consumption in situ. The flexibility of the method is especially important in studies of heritage artefacts, where it is seldom possible to take subsamples which suit fixed container dimensions, and where it may be necessary to study oxidation over extended periods (years). Ways to reduce the response time are also described.

Acoustic emission for tracing the evolution of damage in wooden objects

Abstract: The monitoring of acoustic emission (AE) has allowed direct tracing of the fracturing intensity in wooden cultural objects exposed to variations in temperature and relative humidity (RH). High-frequency components produced by the mechanical fracturing were extracted from the raw AE signals using wavelet transforms. The accumulated energy of these components depended on the magnitude and rate of RH variations. The AE activity became negligible below the allowable magnitude for rapid RH variation established by numerical modelling, or when the time interval allowed for the RH variation was long enough. On-site AE monitoring of a wooden altarpiece in an historic church further confirmed the usefulness of the technique in tracing climate-induced stress in wood. The development of practical AE sensors to indicate risk to wooden objects in museums and at historic sites, or during their transportation, is discussed.

An Investigation of Parameters for the Use of Citrate Solutions for Surface Cleaning Unvarnished Paintings

Abstract: This study investigates the surface cleaning of an unvarnished painting using citrate solutions at a range of pH. Cleaning tests followed a similar method to that used for cleaning paintings. The e...

A review of the phenomenon of lead white darkening and its conversion treatment

Abstract: This paper reviews treatment practices, historical and contemporary, for the conversion of darkened lead white, as informed by accounts in artists' treatises, early paint chemistry manuals and the conservation literature. The evolution of treatment methodology is examined with respect to changing views, conservation ethics, and the impact of various treatment methods on paper artifacts. A discussion of related scientific findings illustrates the recent advances in the understanding of factors contributing to the deterioration of lead white pigment and supports the critical evaluation of conversion treatment methods.

Synthetic organic dyes, 1856–1901: an introductory literature review of their use and related issues in textile conservation

Abstract: The aim of this literature review is to provide a broad introduction to the little-researched subject of early synthetic organic dyestuffs and their use on historic textiles. Early synthetic organic dyes are briefly described, as is the relevant terminology. A brief history of the development of synthetic dyes up to 1901 is given, followed by a discussion of the problems arising from their use in the nineteenth century. Conservation issues relating to early synthetic dyes addressed in the literature from 1950 to 2003 are cited. The extent of use on historic textiles is described. The role of dye analysis in the study of early synthetic organic dyestuffs is indicated, with examples to illustrate its importance. A table of the 22 most commonly used early synthetic dyes is provided with International Colour Index numbers.

An Investigation of Deterioration of Archaeological Iron

Abstract: A small but significant proportion of the archaeological iron objects in the British Museum collection have been problematic in that some of them have required repeated treatment. The deterioration of iron objects during storage was studied using microscopy, Raman spectroscopy, X-ray diffraction, scanning electron microscopy/energy dispersive X-ray analysis, X-ray fluorescence spectroscopy and ion chromatography. A total of 125 iron objects, including 56 from two British Roman sites and 69 from three Anglo-Saxon sites, were studied. Both surface corrosion and corrosion layers on polished cross-sections were investigated. The study revealed that the present condition of the iron objects varies; some are in a stable condition and others have been deteriorating, with pitting and weeping present on the surface. No treatment method had stopped corrosion for every object, although the alkaline sulphite treatment seemed to be more effective than the other methods. The results also showed that chloride io...

Economics of Dust

Abstract: Dust presents a physical risk to objects and reduces evidential value; it also creates a perception of poor standards of care. However, cleaning also imposes risks of damage, takes time and costs money. The presence of visitors induces much of the dust found in properties, so increasing or extending access has implications for housekeeping that are rarely discussed in economic terms, despite the fact that dust control represents the most expensive element of preventive conservation in historic houses. The range of preventive and protective measures that minimize the deposition of dust also carry costs that often relate to visitor flow. Simple economic calculations show the balance between the costs of cleaning and of other equipment and materials in National Trust properties. The cost per visitor initially reduces with increased numbers of people, but at high flow rates expenditure can increase because of the cost of cleaning. The per capita conservation costs become less than UK?2 per visitor at ...

The chemistry of East Asian lacquer: A review of the scientific literature

Abstract: This paper reviews the scientific literature concerning urushi lacquers. Urushi has been used by skilled lacquer artists for thousands of years, predominantly in the East Asian countries of Japan, Korea and China, where there is an abundance of urushi-producing trees. Spectacular lacquered artefacts still exist due to the stability of the material, and numerous conservation efforts endeavour to preserve these pieces. This review discusses the chemical properties of this complex material, with particular reference to its stability and durability, and the conditions that contribute to its deterioration. The importance of understanding these properties is discussed with regard to the conservation of urushi-based objects.

Characterization of yellow dyes in nineteenth-century Chinese textiles

Abstract: The dyes in several specimens of yellow-dyed silk objects in the collection of the Peabody Essex Museum (Salem, MA) were analyzed by high performance liquid chromatography with diode array detector and mass spectrometric analysis, after mild extraction from the silk fibers. Most of these items were goods transported from southern China during the nineteenth century to the Americas on American China trade ships. The objectives of this study were (1) to identify the dyestuffs used in a specific geographical area within a specific time period (i.e. China in the nineteenth century) and (2) to use this knowledge to deduce information about the dyed textiles themselves. It was found that three distinct classes of dye were used: curcumin (from turmeric — Curcuma longa or a similar species), flavonoid (from pagoda tree buds — Sophora japonica) and protoberberine (from huangteng — a species of Fibraurea). Huangteng is unusual in that it actually contains no berberine, but rather the related dye, palmatine. Although huangteng has been reported as having been used as a dyestuff, this is the first report of its being detected in a specific dyed object.

The Influence of Past Protective Treatments on the Deterioration of Historic Stone Façades A Case Study

Abstract: During a 2002 cleaning operation on the Royal Palace (Madrid, Spain), some stains actually became much more visible after the limestone and granite stones were cleaned. These stains were analysed by several instrumental techniques (both in situ and in the laboratory) and were found to result from past protective treatments. Some of these treatments had formed thin, impermeable films that did not allow the water inside the ashlar to evaporate. Sub- and crypto-efflorescences (gypsum, thenardite and nitratite) broke the protective film, generating efflorescences on the surface. The treatments had not penetrated the stone, and the stains were merely superficial. The method used for the cleaning of the stone facades (pressure water jet) was ineffective for the removal of these protective treatments, which at present are deteriorating the stone on which they were applied.

Evaluating Single- and Two-Constant Kubelka-Munk Turbid Media Theory for Instrumental-Based Inpainting

Abstract: Instrumental-based color matching using non-destructive reflection spectrophotometry can be used as an aid in pigment selection for inpainting. This is useful when metamerism is of concern, particularly in modern art where the number of colorants available to artists and conservators is quite large. Simplified methods have been developed for art conservation where a single tint of each pigment mixed with white is required to define a pigment's optical properties based on the single-constant form of Kubelka-Munk (K-M) turbid media theory. Theoretically, this simplification can lead to errors in pigment selection for dark colors and colors not containing a white pigment. Instead, the two-constant form of K-M theory can be used where the model assumptions more closely match the optics of inpainting materials. The two methods were compared using four acrylic emulsion paints with a range of pigment absorption and scattering properties. It was found that the simplified method was inadequate for paints ...

Analyses of Copper- and Beeswax-Containing Green Paint on Egyptian Antiquities

Abstract: Four samples of waxy, green paint from ancient Egyptian objects have been examined. Analysis was performed using infrared and X-ray fluorescence spectroscopy. Each sample was found to contain beeswax and copper. An apparently identical paint could be made by heating together copper and beeswax at 110°C or by mixing copper(II) acetate with molten beeswax. The copper salts of various palmitic and stearic acids were made and their infrared spectra obtained, which led to the conclusion that the green paint contained copper salts of beeswax fatty acids.

The Use of Portable Single-Sided Relaxometry and Laboratory Imaging NMR Devices in Stone Conservation

Abstract: Two nuclear magnetic resonance (NMR) devices, a standard imaging apparatus and a portable single-sided relaxometer (with geometry that allows non-destructive in-situ relaxation measurements on samples of any dimensions), were used to assess the hydrophobic performance of an acrylic polymer (Paraloid B-72) applied as a trichloromethane (chloroform) solution on a biocalcarenite (Lecce stone). The NMR images and relaxation time distribution functions of samples characterized by different treatments were acquired for different water absorption and measurement sequences. Samples were analyzed both fully saturated and during the capillary water absorption. The relaxation results have been compared with NMR images of internal sections of the same samples in the same absorption conditions. In spite of the instrumental and physical differences of the two devices (the single-sided device was tuned to detect the signal from a sensitive volume that is only a small portion of the entire sample, located in the...

Acceptable Light Damage - A Preliminary Investigation

Abstract: An attempt is made to relate the degree of colour change in works of art, oil paintings and watercolours in this instance, to a subjective assessment of how acceptable these changes are over a given length of time. A panel of observers was presented with pairs of reproductions of figurative and abstract oil and watercolour paintings, regions of which had been altered digitally prior to printing to give a known colour difference from the original. In the first part of the study, the observers were asked if a colour difference could be observed, to assess the scale of a Just noticeable difference' (JND) in these complex scenes. In the second part, observers assessed the acceptability of a change over a period of 10, 50 or 100 years. The results demonstrated that the JND is sometimes larger in complex scenes than in simple colour pairs and that changes in smaller areas, more peripheral areas, or areas in abstract images are less noticeable. In the second phase of the study, changes to the figurative...

A Note on a Modern Lead White, also Known as 'Synthetic Plumbonacrite'

Abstract: This article reviews conflicting information found in the literature about the composition and structure of a type of lead white developed in the first half of the twentieth century: pentalead tricarbonate dihydroxide oxide, 3PbCO3·Pb(OH)2·PbO, also known as synthetic plumbonacrite, a pigment that has been described as being 'pearlescent' or 'nacreous'. X-ray diffraction allows pentalead tricarbonate dihydroxide oxide to be distinguished from the more common form of lead white, trilead dicarbonate dihydroxide, 2PbCO3·Pb(OH)2. X-ray diffraction data for the two compounds are given, as well as for lead carbonate, PbCO3, which is often associated with trilead dicarbonate dihydroxide. Experimental data are presented for several paint samples in which pentalead tricarbonate dihydroxide oxide was found. These samples were also characterized by polarized light microscopy and scanning electron microscopy. Although some samples were found to be pearlescent or nacreous in appearance, others were not.

The Correlation between Bulk Density and Shock Resistance of Waterlogged Archaeological Wood using the Pilodyn

Abstract: The correlation (R2 = 0.87) between bulk density and the shock resistance of homogeneously and heterogeneously degraded waterlogged archaeological wood, with densities ranging from 100 to 700 kg·m-3, was determined using the Pilodyn wood tester. The results showed that the energy required to fracture a given mass of wood substance was constant (R2 = 0.83) and independent of wood species. However, measurements in the three main orientations (longitudinal, radial and tangential) showed a significant variation and therefore further measurements were preferentially taken in the radial axis. A model to enable the determination of the average bulk density of waterlogged wood from the depth of penetration of the Pilodyn showed that the average bulk density of homogeneously and heterogeneously degraded waterlogged wood could be determined with an average accuracy of ± 9%. A high correlation coefficient (R2 = 0.995) for measurements taken in water and air enable the Pilodyn to assess waterlogged wood under...

The vicissitudes of vivianite as pigment and corrosion product.

Abstract: Vivianite, hydrated ferrous phosphate, Fe2+ 3(PO 4)2˙8H2O, can be formed in the soil under reducing conditions. It occurs in wet clay soils, in the presence of a source of phosphate ions such as decomposing bone, and in the absence of sulphur compounds. As an iron corrosion product it sometimes preserves iron finds in excellent condition. When exposed to air, it undergoes oxidation to Fe3+ -containing species, which cause a shift in colour from pale blue to darker blue or blue-green. Vivianite has also been used as a pigment, and the number of published occurrences has been increasing steadily over the last few years. It can discolour, a problem encountered in both Romanesque wall paintings and seventeenth-century Dutch paintings. The occurrence of vivianite as a pigment is sufficiently rare to provide information on dating and provenance. All published occurrences of the pigment to date are reviewed.

Determination of maximum freeze drying temperature for PEG-impregnated archaeological wood

Abstract: A series of experiments, cooling aqueous solutions of polyethylene glycols (PEGs) with molecular masses ranging from 1000 to 10000 to full solidity followed by heating to full liquefaction, combined with measurement of the physical stability, was performed. The experiments were carried out using everyday metal thermos flasks, a domestic freezer and a simple temperature data logger. These experiments gave standard curves for eutectic temperatures, thawing temperatures and strength properties as a function of the molecular mass of the PEG. The experiments showed that the softening and thawing temperatures for aqueous PEG solutions are higher than the solidification and eutectic temperatures. These key properties can be used to find the highest temperature at which PEG and water are still solid, thus minimizing the time and energy spent on the freeze drying process, which requires that no liquid phases are present in order to prevent collapse. The methods, based on simple procedure and equipment, can...

A Study of the Composition of Chinese Blue and White Porcelain

Abstract: Blue and white Chinese porcelain specimens from Dehua and Zhangzhou kiln sites from the Ming dynasty (AD 1368–1644), and Jingdezhen kiln sites from the Yuan (AD 1280–1368) to Ming dynasties were collected. The chemical compositions of these valuable samples were determined using energy dispersive X-ray, fluorescence (EDXRF) spectrometry, a non-destructive method, and some Jingdezhen samples were analyzed by scanning electron microscopy and transmission electron microscopy. The EDXRF results were subjected to correspondence analysis. Differences in the composition of the specimen bodies were found for specimens from different production sites. The blue and white Jingdezhen imperial, porcelain from the Yuan to Ming dynasties can be divided into two periods based on differences in the chemical composztion and microstructure of the pigments. The reasons for these variations are discussed.

Characterization of Furunori (Aged Paste) and Preparation of a Polysaccharide Similar to Furunori

Abstract: Furunori (aged paste) is a conservation material that is used for Japanese painting conservation. Furunori is a smoother and weaker adhesive than fresh paste, and it enables the surfaces to be easily peeled apart, with application of water, in a future conservation. Due to these characteristics, furunori has traditionally been used for attaching the backing paper to paintings in Japan, because it is considered that furunori causes less stress on the paintings than fresh paste. This study aims to clarify the characteristics of furunori based on chemical analysis and examination of the microorganisms involved in the early stage of furunori generation. Based on the results obtained, a polysaccharide similar to furunori was prepared.

Australian Aboriginal bark paintings - their history, structure and conservation

Abstract: The cultural background of Aboriginal bark paintings, an important factor in understanding their structure and deterioration, is described. Issues relating to the structure, properties and deterioration of Eucalyptus Tetrodonta bark used as a painting support are discussed. Traditional and modern pigments and binders that were used are listed. Deterioration of the paint layer is the major reason for conservation treatment. The range of conservation treatment methods and materials for both the bark support and paint layer are reviewed. Past and present display and storage approaches are outlined.

Materials and Techniques of a Spanish Renaissance Panel Painting

Abstract: A technical examination of a Spanish altarpiece attributed to Bartolome Bermejo (1468–1495), belonging to the Hispanic Society of America, was carried out. Analytical methods used in this study were X-radiography, infrared reflectography, optical microscopy (reflected light and polarized light), cross-section staining tests, scanning electron microscopy, gas chromatography–mass spectrometry, Fourier transform infrared spectroscopy and carbon-14 dating. A number of unusual techniques were identified including: the use of cotton and flax fibres for internal strength in the halo relief, the lack of a bole layer, the use of an orangecoloured oil mordant under the gilding, the use of powdered gold over the entire gilded surface and the use of an egg-white binding medium. The carbon-14 dating placed the panel in the 1530s, which will lead to a new attribution.

Spherical Copper Resinate on Coromandel Objects : Analysis and Conservation of Matt Green Paint

Abstract: An unusual green pigment was found on a seventeenth-century kuan cai (Coromandel) lacquer screen at the Victoria and Albert Museum, London. The particles are perfectly spherical and translucent, with the appearance of green fish roe. Analysis revealed that the pigment is a copper resinate, produced by reacting a copper salt with a resin, probably one from a Pinus species. The binding medium for the pigment is proteinaceous. The unusual spherical morphology of the particles results from the method of manufacture. A pigment with the same microscopic appearance was also found on two other Coromandel objects from the same collection. In light or olive green areas, where the pigment is mixed with lead white, the paint is glossy and well preserved. In contrast, in the dark green areas where the pigment was used alone, the paint is matt and powdery and there is significant paint loss and abrasion. The problem of consolidation of the powdery paint, while still preserving the matt appearance of the surface, was resolved by the use of immiscible solvents and consolidant.

An Evaluation of the Role of Semi-Transparent Relining in the Conservation of Thangka Paintings

Abstract: Thangkas (Tibetan painted banners) are composite objects and, when in use, they are frequently rolled and unrolled. The painted part is rendered on both sides and often bears an inscription recalling the thangka's consecration ceremony. These inscriptions should not be obscured as they give spiritual dimension to the thangka. After briefly describing the technique of Tibetan painting and the most frequently encountered conservation problems, the issue of relining is discussed, keeping in mind the need for legibility of the inscription and respect for the material characteristics. Collaboration between painting and textile conservators is essential. A technique of transparent relining with silk crepeline using reactivation of acrylic adhesive and hand pressure is proposed, which respects both the physical characteristics and spiritual meaning of the thangka. It also proves safe and efficient in consolidating the damaged elements. Alternative approaches using materials available in the Himalayan reg...

Digital Reconstruction of Fragmented Archaeological Objects

Abstract: : Archaeological objects are often discovered broken into many pieces, and reassembling the original object by solving the 'three-dimensional puzzle' is a time-consuming and expensive task, referred to here as the fragmentation problem. This paper describes a methodology that can facilitate the matching of fragments from broken objects, with the use of statistical analysis and three-dimensional computer models. First, the nature of three-dimensional computer models of archaeological objects is explained, emphasizing the benefits of using unit normal vectors to characterize their surfaces. A computer-based model of such an object can be separated into clearly defined and different surfaces through a process called segmentation.The resulting segments are then subjected to a novel statistical analysis, which is based on the calculation of eigenvalues of the unit vectors in Riemannian space. This allows the fragments' surfaces to be characterized, and it is this characterization that leads to fragment matching. As part of the research, a pilot study was undertaken using objects from the Propylaia of Athens and ancient Messini. The results are presented and ways proposed of both improving the methodology and using it in other conservation-related applications. This study took place at the Acropolis, Athens, one of the most significant world heritage sites for archaeological building conservation.