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- Damage mechanism (2)
- Deterioration (2)
- Emission (2)
- Gold mosaics (2)
- Klimamessungen (2)
- Quecksilber (2)
- Wood protection (2)
- Zinn-Amalgamspiegel (2)
- 13C NMR (1)
- 29Si NMR (1)
Organisationseinheit der BAM
With the implementation of glass casting in France in the second half of the 17th century, larger mirrors could be produced. So-called tin-mercury mirrors were made by coating glass with tin amalgam. Today, many historical mirrors are partly damaged, the image quality is compromised, and the material integrity of the mirror is threatened. The transformation from tin into an oxide starts at the surface of the amalgam and proceeds down to the glass surface. The mercury dissolves as a liquid or gaseous phase. The amalgam layer is destroyed, so that conservation is necessary. Conservators must follow strict safety precautions while handling amalgam mirrors because of possible mercury emissions and corrosion of the amalgam, during which elemental mercury accumulates near the mirror frame in droplets and is emitted into the air.
In a research project, the quantity of the mercury emissions from historical mirrors was examined and a technique to decrease these emissions was developed.
ESEM-EDX analyses for the characterisation and reproduction of nineteenth-century gold tesserae
(2012)
Environmental scanning electron microscopy with energy dispersive X-ray analysis (ESEM-EDX) is a versatile working tool for the examination of gold tesserae as well as for the selection of suitable materials for their reproduction. In this paper, the ESEM-EDX analyses of original gold tesserae and their damage types are presented. These analytical results form the basis for further calculations of glass properties and experiments. These calculated values enable the determination of the relevant glass properties and allow us to choose the appropriate type of modern glass for further experiments. Subsequent experiments convert this knowledge into practice. By comparing the analytical results from the original glasses and the replicas the accuracy and precision will be shown.
To improve the adhesives used for restoring stained glass windows, various adhesives were tested and modified. Stained glass windows often show gaps that are too wide to be glued with conventional adhesives, and complementing the gap with spare glass is very time-consuming.
To solve this problem, a filler with improved adhesive strength was developed to bridge wider gaps and cracks. The new filler combines glass adhesives with specially treated glass powder.
Three different glass adhesives were selected and mixed with the specially treated glass powder. The adhesive – glass powder mixture developed was then subjected to accelerated aging and analysed with Fourier transform infrared analysis, scanning electron microscopy, colourimetry, and bending and tensile tests. The results were excellent and the mixture was subsequently used to restore glass windows from four 19th-century churches and chapels. The restoration process was described in conjunction with the advantages of using this approach.
This new adhesive – glass powder mixture provides an adhesive process that can be adapted to the special needs of any object being restored and thus provides a ready answer to the specific damage of each object.
It has been shown that tetraethoxysilane-derived precursors are suitable solutions for impregnating pine sapwood to improve its dimensional stability. Tailored sol–gel syntheses result in precursors with nano-scaled silica species which are able to penetrate into the cell walls of wood. The physical fixation of those species inside the cell walls was verified by ESEM/EDX investigations. There is evidence that the silica species are chemically bonded to wood components. Nonreacted alkoxy groups can exist in the wood composites after impregnation. The amount of these organic residues depends on the composition of the precursors, especially their condensation degree and reactivity. Treatments for finishing the composites after the impregnation step to get clean products and stable properties are discussed in this context. An explanation of the complex relationship between solids content in the impregnation solutions and percentage weight gain and bulking of the composites is given. It can be demonstrated that high WPG values (>20 %) are pre-conditions for an effective protection of the resulting composites but they only guarantee efficient improvements if connected with the incorporation of the inorganic component inside the cell walls. Therefore, the sol–gel syntheses have to be carried out in such a manner that very small (<2 nm) as well as reactive species are sufficiently available. This demands syntheses using sub-stoichiometric water contents (H2O/TEOS <4, better <2).
A number of environmental monitoring projects were performed on historic stained-glass Windows in Germany from 1994 to 2012. The quality of the protective glazing was assessed by recording environmental Parameters in the interspace between the original and the protective glazing and on the inside of the original window. Tor this purpose, temperature, humidity and air velocity were measured. Particles were sampled with different methods and analysed by scanning electron microscopy combined with energy dispersive X-ray spectroscopy to determine their chemical composition. The effect of particles on model glass samples was investigated in climate chambers under accelerated weathering conditions. The results from in situ measurements and laboratory tests were combined to evaluate the potential effect of particulate matter on historic stained-glass Windows.
The solgel process was applied to enhance properties of pine sapwood. For this purpose wood prisms were soaked in nanoscaled precursor solutions prepared from titanium(IV) n-butoxide and titanium(IV) iso-propoxide, respectively, using vacuum impregnation technique. The wet composites were cured by special program with final heat treatment at 103 °C. Weight percent gains (WPG) of the wood specimen in the range of 19-25% were obtained due to these procedures. SEM investigations show that precursor solutions penetrate into the whole wood body and the titania formed after heat treatment in the composites is deposited in the pores (lumen) and partly in the cell walls of the wooden matrix. The moisture sorption was investigated in long term tests for a period of some months by storage at 20-23 °C in humid air (relative humidity of 99%) and ambient atmosphere (relative humidity 40-60%), respectively. For untreated reference samples the moisture sorption results in increasing of mass and volume according to saturation values of 24 and 13%, respectively, after about 15 days. The incorporation of titania reduces the saturation values of the moisture sorption by up to 12% in mass and by up to 5% in volume at a relative humidity of 99%. Thus, an enhancement of the dimensional stability of about 60% is obtained at best. The results demonstrate that modification of wood with sol-gel derived precursors can enhance its dimensional stability, which prevents the formation of cracks. Because of that reduced moisture sorption biological attacks should be delimited. Additionally, thermal analyses show a retarded combustion of the wood matrix due to titania infiltration.
The antileaching efficacy of sol-gel-derived TiO2- and SiO2-based precursors has been evaluated through laboratory leaching trials with pine sapwood in two different ways. In a one-step process, wood was vacuum impregnated by the precursor solutions containing CuCl2. The copper (Cu) emission rates of the sol-gel-based impregnated woods were up to 70% lower than that of wood treated with pure CuCl2 solution at the same level of concentration. More improvement (80%) could be achieved in a two-step process, in which sol-gel precursors were introduced into an already CuCl2-treated wood. The refinement was attributed to several effects. In the one-step approach, Cu was embedded in the TiO2/SiO2 gels formed in the wood texture. During a two-step impregnation, gel layers that were formed in the wooden interior acted as an effective diffusion barrier. The sol-gel impregnations made wood more hydrophobic; therefore, the low amount of water that penetrated the cell wall was less efficient to leach out Cu.
In this study, bulked adhesives were examined regarding changes in properties for their use in the restoration of stained-glass windows. Two epoxy adhesives commonly used in the restoration of flat glass, Araldite® 2020 and Hxtal NYL-1™, were investigated. The adhesives were mixed with various silica-based micro- and nano-particles as fillers. Different tests were carried out on the adhesives with and without fillers in order to characterise their chemical and mechanical properties. The tests included colorimetry, dynamic-mechanical methods of analysis and tests on bending strength. No property changes could be ascertained in the bulked adhesives that would be negative for the restoration of delicate flat glass.
Several restoration projects of stained-glass windows have been performed in Lower Silesia (Poland) since 2010. The aim of the projects was to protect stained-glass windows against environmental impact of industial pollutants and acid rain by installing a protective glazing. The usefulness of protective glazing has been proved by climate measurements and determination of environmental impact before and after installation.
The present study contributes to the controversial discussion in the literature whether Si–O–C bonds in wood–silica–gel composites exist. 13C NMR is a suitable method to proof such bonds. Because of the low concentration of 13C isotopes in natural wood, 13C cellulose was used as 13C-enriched substitute. A tailored sol for the impregnation of that cellulose was chosen by liquid 29Si NMR pre-investigations of various sols whose reactivity and stability were time-dependently analysed. It is based on a sub-stoichiometric hydrolysis of tetraethoxysilane (TEOS) with 1 mol water per mol TEOS. Thermal analyses were performed to show a comparability of the thermal behaviour of wood–silica–gel and cellulose–silica–gel composites. There are two strong hints of the existence of stable Si–O–C bonds: (1) by thermal analysis, a shift in the fire behaviour of 100 K can be observed with a change in pyrolysis behaviour of the composite and (2) the proof by REDOR NMR that a dipolar coupling between 1329Si and 13C nuclei exists.
Corrosion of historic timber
(2014)
With the implementation of glass casting in France in the second half of the 17th century, larger mirrors could be produced. So-called tin-mercury mirrors were made by coating glass with tin amalgam. Today, many historical mirrors are partly damaged, the image quality is compromised, and the material integrity of the mirror is threatened. The transformation from tin into an oxide starts at the surface of the amalgam and proceeds down to the glass surface. The mercury dissolves as a liquid or gaseous phase. The amalgam layer is destroyed, so that conservation is necessary. Conservators must follow strict safety precautions while handling amalgam mirrors because of possible mercury emissions and corrosion of the amalgam, during which elemental mercury accumulates near the mirror frame in droplets and is emitted into the air.
In a research project, the quantity of the mercury emissions from historical mirrors was examined and a technique to decrease these emissions was developed.
A comparative study tested the performance of modern anti-corrosion Systems against that of traditional red lead Systems.
One aim of the research project was to find alternatives for the use of a red lead priming coat, the Standard anti-corrosive primer for iron and Steel in the past but a material which endangers health as well as environment. The investigation aimed to determine whether anti-corrosion Systems developed for industrial use were suitable for the Conservation of historic iron and cast iron objects.
Besides coatings containing red lead, several surface tolerant coatings with different anti-corrosion pigments were examined.
The modern anti-corrosion Systems examined were suitable for surfaces where Optimum surface preparation is not practical.
They were applied to both historical samples and to newly prepared model samples.
After uniform pre-corrosion, the model samples were coated and underwent two different ageing procedures: accelerated ageing in a climate chamber and outdoor weathering on a test site with moderate city climate. The specimens were exposed for more than two and a half years. Evaluation of the artificially aged samples was carried out under the aspect coating degradation, tensile strength test, cross-hatch test and Fourier-transform infrared microscope.
The results of the research with optical evaluation and test procedures will be presented. The two ageing methods will be discussed, with different results from the naturally and artificially aged samples. The results Show a similar eligibility of modern anti-corrosion Systems as compared with red lead Systems for the use in Conservation.