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The mechanical properties of early artist's acrylic paints were investigated under controlled aqueous additive leaching for the purpose of identifying changes caused by cleaning paintings with water. Strength and stiffness values were obtained using a tensiometer to collect stress-strain curves of paint films. The results were compared to those from similar experiments in which paint films were tested under various age, temperature, and relative humidity (RH) values. Strength and stiffness both increased with decreased temperature, decreased RH, increased age, and increased additive removal. The most significant impact on mechanical properties was caused by lowering temperature to the Tg region around 5°C. Dramatic changes in properties were caused by RH fluctuations; however, the magnitudes were negligible in comparison to those induced by low temperature. Removal of water-soluble additives produced a uniform increase in tensile strength and secant modulus at all RH values. The films were equally responsive to fluctuations in RH before and after additive leaching. In comparing the material properties across a wide range of conditions it is evident that the acrylic paints in this study were not significantly altered by the amount of water exposure involved in cleaning paintings.
A review of the applications of electrochemical methods to the conservation of metal artifacts is presented with regards to their use in treatment and research. As treatment techniques electrochemical methods have been used for cleaning, stabilization and consolidation for many years. Presently electrochemical methods are increasingly being used as a research tool, allowing the identification and quantification of products present at the surface of the artifacts as well as evaluation of the compatibility between materials. Examples of application to silver-copper alloys and stainless steels are presented.
This paper addresses some of the conservation concerns of artists' acrylic paints by investigating the chemical changes of the paint films caused during a one-hour exposure to water experiments and the rate at which some of the changes occur. Three different acrylic paint films were investigated. Real-time capillary rise, conductivity measurements and thermo-mechanical analysis (TMA) gave an indication of the rate at which these changes occurred. Much of the measurable leaching occurred within the first 20 minutes of the paint film being exposed to water, while the most rapid leaching occurred within the first five minutes, before approaching an equilibrium state. All physical and visual changes in colour, gloss, dimension, mass and surface morphology (using atomic force microscopy, AFM) were monitored. A decrease in size and mass indicated that material had been permanently removed from the paint films. Gloss and colour measurements, as well as AFM images, also showed evidence of changes caused by the exposure to water.
Mokumé Gane layered metal is a 300-year old decorative metal laminate technique peculiar to the isolated culture of the Japanese Shogunate. Like many complex craft practices handed down through individual experience, the manufacture and development of Mokumé Gane has changed minimally over time. The application of contemporary metallurgical knowledge and solid state bonding techniques such as Hot Press Diffusion Bonding and Hot Roll Bonding provide for further development of Mokumé Gane: bonding success rates are improved, and manufacturing times are reduced. In addition, the range of possible metal combinations is substantially increased; 42 different combinations to date have been successfully bonded, including a new type of Mokumé Gane employing aluminium alloys. This research has allowed a very large increase in the variety of colours, patterns, and visual effects, available to contemporary metalsmiths and jewellers.
Severe decay of the stone façade of the Pyramid of Quetzalcoatl, one of the more remarkable structures in the World Heritage Site archaeological zone of Teotihuacan, Mexico, is caused by the presence of humidity and salt crystallization. The floors were analyzed to determine whether water and salts were filtering up from the ground and to find a way to reduce the penetration of water. Analyses of the lime plaster and organic matter were carried out by traditional wet chemical methods in order to discover the possible recipe that is the basis of the technology used by Pre-Columbian masons. The presence of an organic mucilage and fiber was identified. The organic components of the floors were analyzed using FTIR of extracts, while mucilage from leaves of a local cactus, Opuntia sp, that is used traditionally as a cementing material in plasters, was analyzed for comparative purposes to determine whether the mucilage was also used in pre-Columbian times. X-ray spectrometry and x- ray diffraction were also used to complement the study to identify the mineralogy of the plasters. This study shows that the Teotihuacanos used a composite material that has great durability, permitting the survival of the floors for almost 2000 years, but that also is succeptible to damage in a modern, stressed environment with high tourist traffic.
A customary procedure in the protection of monumental buildings is the consolidation of decaying stone by the application of commercial products containing tetraethoxysilane (TEOS). These products polymerize within the porous structure of the decaying stone, significantly increasing the cohesion of the material. However, TEOS-based consolidants suffer practical drawbacks, such as cracking of the network during the drying phase, and significant blocking of the rock pores. These limitations are related to the growth of a dense microporous network of the xerogel inside the stone material, which is typical from TEOS sols. Therefore, the purpose of this work is to increase porosity of the product by including colloidal particles in the starting sol.
We prepared a colloid-polymer composite gel using TEOS and a commercial silica colloid. The percentage by weight of silica colloid particles to total silica was 54%. Ethanol and dibutyltindilaurate (DBLT) were chosen as solvent and catalyst, respectively. This catalyst promotes the gelation at a neutral pH, preventing stone decay related to acid or basic catalysis. We characterized the properties playing a key role in consolidation. Data were compared with those obtained using a popular commercial product: Tegovakon V 100 produced by Goldsmith.
In spite of the colloidal particle addition, sols exhibited viscosity values close to those of the commercial products, as a consequence of their dispersion in ethanol. A gelation time similar to that of commercial consolidants was maintained, whereas the contained sol was stable over a period of up to six months. Concerning textural parameters, the addition of colloid permitted to obtain a crack-free, mesoporous material structure. This generated a crack-free material whereas the gel from Tegovakon V 100 exhibited cracking.
We also evaluated the consolidant efficacy on a biocalcareous stone, one of the most common monumental building stone employed in the southwest of Spain. Three key parameters -penetration depth in the rock, mechanical properties and water vapour diffusivity- were measured. Stone permeation was similar to that from the commercial product. Notably, a significant improvement of compression strength of the stone was observed. Reduction in vapour diffusivity of the treated stone was slightly lower for our gel than for the commercial consolidant.
The stiffening and embrittlement of oil paints over time has been a real concern for those responsible for the long term care and preservation of paintings. This paper examines the effects of time, pigments, relative humidity (RH), temperature and solvents on the mechanical properties of traditional oil paints. In this way it is possible to determine the role of each factor in causing the paints to become brittle. Even after 14 years the oil paints show little evidence that the long term “maturing” processes have begun to slow down. It is shown that there seems to be little correlation between the time paint requires to “dry-to-the-touch” and the longer term mechanical properties. Both low and high temperature levels can increase the stiffness of the paints though the mechanisms are quite different. Considerable hydrolysis of the paints occurs early in their history and the ones that hydrolyze most quickly are the ones that remain the most flexible.
A rare collection of cast votive images (ex-votos ) made of beeswax were found in the 1940s behind the cresting of a screen above the tomb of Bishop Edmund Lacey in the Cathedral Church of St. Peter in Exeter, England. Some of these fragmentary, aged and brittle waxes, dating to the late fifteenth to early sixteenth centuries A.D., served as the basis to further test the cleaning of dirt and accretions using a Q-switched Nd:YAG laser. Because of the low melting point of the wax, observations made of the effects on the wax substrate due to heat emitted from the laser were critical to establish the efficacy of the cleaning method. Preliminary optical microscopy was used to establish a typology of the waxes based on their condition, color, and nature of the weathering phenomena. Several techniques were used to characterize the waxes and the surface deposits, including gas chromatography-mass spectroscopy (GC-MS), energy-dispersive x-ray fluorescence (EDXRF) and scanning electron microscopy (SEM-EDS), in addition to simple tests of melting point and hardness that served to help understand the nature, condition and treatment of the waxes .
We demonstrate the potential of Raman spectroscopy as an on-site technique for the characterization of ancient ceramics. This non-destructive analysis offers a way to get information on the process and even sometimes on the date of ancient artifacts. Much information remains written in the microstructure of ceramics bodies and in the nanostructure of glasses, glaze and enamels. Raman signatures are specific to the technology that was applied to a given starting batch and to the process of manufacture. Recent studies that demonstrate: i) the use of cassiterite for opacification and its role in Islamic three-color wares and polychrome lustred pottery from the Abbasid to Fatimid period, ii) the invention of the “hybrid-paste porcelain” by the Duke of Medici, known as Medici porcelain and of the “soft-paste” porcelain by the French Manufactures in the eighteen century (Chantilly, Mennecy, Saint-Cloud), iii) the development of the underglaze pigment technology by Iznik and then Kütayha Ottoman potters; iii) the use of lapis lazuli gem as an unexpected pigment in the Iran Lajvardina wares. Finally we explore the relationship between glass makers and potters.
Digital Scanning Calorimetry (DSC), a thermal characterization technique, can be used to rapidly obtain a rough upper estimate of the firing temperature of archaeological pottery as well as an indication of its composition. The technique involves heating a small sample (10–20 mg) of ground ceramic above the vitrification temperature, cooling and reheating. The curves of the two heating cycles are then compared. The validity of the technique was evaluated by a blind test in which 35 tiles fired at different temperatures were analyzed without knowing their firing point, and by analysis of archaeological pottery samples assumed to be local or imported based upon stylistic criteria.
Atomic oxygen treatment has been investigated as an unconventional option for art restoration where conventional methods have not been effective. Exposure of surfaces to atomic oxygen was first performed to investigate the durability of materials in the low Earth orbit environment of space. The use of the ground based environmental simulation chambers, developed for atomic oxygen exposure testing, has been investigated in collaboration with conservators at a variety of institutions, as a method to clean the surfaces of works of art. The atomic oxygen treatment technique has been evaluated as a method to remove soot and char from the surface of oil paint (both varnished and unvarnished), watercolors, acrylic paint, and fabric as well as the removal of graffiti and other marks from surfaces which are too porous to lend themselves to conventional solvent removal techniques. This paper will discuss the treatment of these surfaces giving an example of each and a discussion of the treatment results.
We report on a study of ultramarine pigments via Colorimetry, resonance Raman, and 27Al, 29Si solid-state NMR spectroscopy. NMR parameters are shown to correlate well with the intensities of Raman signals corresponding to the chromophores S3−. and S2−.. Further, a correlation is established between the colorimetric parameters L* (lightness) and C* (chromaticity) and the paramagnetic shift in NMR spectra for both 27Al and 29Si. The parameter h (hue) appeared not to vary over the range of paramagnetic host concentrations studied. Preliminary results on faded pigments in both acidic and basic media show that the concentration of diamagnetic guest molecules in the sodalite lattice rises, and some of the paramagnetic species are replaced.
The combination of Raman spectroscopy and Secondary Ion Mass Spectrometry can improve understanding of the chemistry of the glass alteration process. Formic and acetic acids play an important role in the alteration of museum glass objects placed in a humid atmosphere. Raman spectroscopy indicates that the soda-rich glass structure is modified differently when exposed to a humid versus a humid and polluted atmosphere at 60°C. Formic acid was not formed from soda-rich glass in the presence of carbon dioxide, high humidity and light.
As linseed oil ages, hydrolysis and oxidation produce acid groups on the polymer chain that may lead to ionomeric behavior. The effect of these changes is difficult to determine in old paints because of the lack of records of environmental and treatment histories that can alter the physical properties significantly. A series of paints were made that have chemical properties similar to those of aged paints and that mimic old paints. Their properties seem to show flexibility as well as coherency but low strength and a high susceptibility to solvents.
Recent developments in the understanding of the low-magnesia soda-lime-silica or “natron” glasses of the first millennium A.D. are reviewed. It appears that glass production was divided between a small number of primary glass making centres, situated mainly in the Near East, and a large number of secondary fabrication workshops that remelted and shaped the lumps of raw, premelted glass. Glass may be related to its primary production group by elemental analysis and, where there are data from workshops, to the production centre or region. The recycling of old glass is revealed by trace element analysis, due to the contamination of primary glass compositions by small quantities of coloured glass incorporated in the recycled material. The analysis of isotopes of Sr and Pb allows the geological environment of the raw materials to be inferred and in some cases, provenance to be predicted.
Terra sigillata ceramic is a fine ware produced during the Roman period. Its great success was due to its remarkable gloss, also called slip, which provides a bright deep red aspect. TEM-EELS and XRD techniques were used to understand the sub-microscopic origins of this singular aspect. Analysis investigations on five samples of two important Gaul workshops are described here. It appears that those samples have the same slip structure: sub-microscopic hematite and corundum crystals in a glass matrix. The matrix does not contain metallic ions, hematite is substituted in Al and Ti while corundum is substituted in Fe. The two crystal populations are homogeneously dispersed in the matrix and, together, give the specific red-orange colour to the sigillata.
The chloride bearing corrosion product akaganéite (βFeOOH) can form during postexcavation corrosion of chloride infested archaeological iron and is able to corrode iron in contact with it. Its action on iron is examined using βFeOOH synthesized from ferrous chloride and iron powder. Using weight measurements the hygroscopicity of βFeOOH is established. The influence of relative humidity on the corrosion of iron powder mixed with βFeOOH is examined by dynamic mass change within a climatic chamber. At 20°C and 12% relative humidity, iron in contact with βFeOOH did not corrode. At 15% relative humidity slight iron corrosion was detected after 160 hours, but at 35% relative humidity corrosion occurred after a few hours. Surface adsorbed chloride was removed from βFeOOH by aqueous washing and this reduced its hygroscopicity. The reported metastability of βFeOOH was examined via XRD of a 23 year old sample, which was found to be still entirely composed of βFeOOH. These results provide better understanding of βFeOOH corrosion of iron, corrosion control of chloride infested iron using dry storage and the effect of aqueous washing on archaeological iron.
In the light of new documentary information regarding the range of materials available to sixteenth century artists, cross sections from paintings were re-examined using scanning electron microscopy - energy dispersive spectrometry. Among a variety of new materials, colored glassy pigments were found including diverse yellow glassy particles, specifically lead silicate and a glass colored by lead antimonate. These are the “yellow smalts” described in Renaissance writings on artists’ materials.
Reverse engineering past craft technologies involves using the basics of materials science and engineering to a new end: their preservation and continuation. Examples are presented of the glazed tile technologies of Samarkand, Bukhara and other Silk Route cities of Uzbekistan that date from the thirteenth century A.D. but that continue to the present. The UNESCO charter for the preservation of Intangible Cultural Properties has enlightened the goals and results of the research and has linked together archaeological materials research and conservation science in an exciting new partnership.
Scanning electron microscopy/energy-dispersive X-ray spectrometry (SEM/EDS) was used to characterize the composition of glazes found on a collection of blue glazed, white quartzite sculptures, excavated from 1913–1916 by the Harvard University–Boston Museum of Fine Arts Expedition at the site of Kerma, the capital of ancient Kush, in today's Sudan. The scientific analysis of these artifacts shows the experimental nature of this extremely rare manufacture which appears to have developed out of faience technology.