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Naturwissenschaft meets Kunsthistorik Provenienzbestimmung eines mittelalterlichen Glasgemäldes
(2007)
Untersuchung historischer Goldmosaike - Herstellungstechnologie und charakteristische Schadensbilder
(2009)
A research project of reconstructing historical gold mosaics deals with reconstructing weatherproof gold and silver mosaics according to historical models.
The gold mosaics examinded originate mainly from germany from 1880 to 1920 and are composed of three parts. They consist of a matching support glass, the gold or silver layer and a cover glass. By examining the morphology and layer thicknesses with the ESEM, and using chemical analysis with the EDX, the relationship of glass composition and damage patterns was established. The glass analysis provided quantitative composition data and made it possible to determine its chemical stability. It supplied the basis for calculating glass characteristics and was referred to when casting suitable historical mosaic glass. The analysis of the qualitative composition of the gold and silver layers also served as a model for reconstruction. After testing selected reconstructed gold mosaics in the climate chamber, the ESEM was used for capturing leaching and other process data and the glass composition was optimized accordingly. Over 100 predominantly historical gold mosaics were analyzed and the results entered into a database which can now be consulted for comparative investigations to determine both origin and date.
Die vorliegende Untersuchung befasst sich mit der Frage, inwieweit mit Füllstoff angereicherte Klebstoffe für die Restaurierung von Flachgläsern mit größeren Defekten oder als Ergänzungsmaterial geeignet sind. Hierzu werden verschiedene silikatische Füllstoffe untersucht und in ausgewählte Glasklebstoffe eingearbeitet. Die Zugabe der Füllstoffe ermöglicht eine gezielte Eigenschaftssteuerung von z.B. Viskosität oder Härte. Die eingesetzten Füllstoffe werden hinsichtlich ihrer Zusammensetzung und Korngröße charakterisiert und mikroskopisch betrachtet. Die optimale Dispergierung der Füllstoffe in die Klebstoffe wird ermittelt und in Testreihen überprüft.
Die angefertigten gefüllten Klebstoffe werden durch Farb- und UV-VIS Messungen charakterisiert. REM-Aufnahmen geben Aufschluss über die Verteilung der Füllstoffe im Klebstoff. Tests zur Biegefestigkeit sowie die Durchführung dynamisch-mechanischer Analysen (DMA) ermöglichen Aussagen zum Alterungsverhalten der Klebstoffe. Dazu werden die Prüfkörper vor und nach der Alterung im Klimaprüfschrank untersucht.
Die Ergebnisse zeigen, dass sich durch die Beimischung von Füllstoffen Eigenschaften wie Festigkeit, Elastizität und auch Vergilbungsbeständigkeit beeinflussen lassen. Im Praxisbetrieb in den Restaurierungswerkstätten ist es jedoch schwierig, eine optimale Mischung der Komponenten zu erreichen. Dies begrenzt die Verwendung der getesteten Füllstoffe als transparentes Ergänzungsmaterial. Im Versuchsverlauf konnten dennoch vielversprechende gefüllte Klebstoffe entwickelt und auch die Transparenz verbessert werden. Die Testergebnisse werden vorgestellt und erläutert.
Initial situation:
Aluminum is an often-used building material in modern architecture, not only for construction but as well for facades and decorative elements. In the 1950th and 1960th, after World War II, many buildings in Germany were constructed with aluminum or contain elements of colored anodized aluminum. In the last years a larger number of these buildings are increasingly in the sight of conservation works including the aluminum parts such as window frames or facade coverings.
Damaged Aluminum Surfaces:
Common damages are a change of color or gloss changes through weathering processes, drill holes or marks due to later modifications, scratches in the anodized layer due to extensive wear e.g. at handrails or door handles.
To repair damaged aluminum surfaces, there are usually two options: smaller damaged areas are repaired by using a touch-up pen. In case of larger damages, the complete re-anodization is necessary. This includes to de-anodize the surface with cleaning and grinding the whole aluminum object. Both possibilities are disadvantageous for the objects. The touch-up pen often does not match the color of the original surface together with an insufficient corrosion protection for outdoors. While the newly anodized surface differs in color and gloss from the originally applied color.
Research Approach:
The whole procedure contrasts with the principal approach in conservation which aims to intervene as less as possible, in case of the conservation of an object. To fulfill this approach in a more appropriate way the research project focuses on a mobile and partial application for colored, anodized aluminum parts.
To anodize aluminum the application of an electrolyte onto the surface together with sufficient voltage and current is necessary. Generally diluted sulfuric acid is used as electrolyte. Different possibilities are examined to enable the mobile application of the electrolyte, e. g. the application by producing a gel matrix or like in electroplating by pen or brush wrapped with a fleece fabric.
Experimental part:
First experiments are conducted to examine the structure of the anodized layer in relation with proper cleaning, anodization time with applied voltage and current and the coloring process. The aim was to reduce the preparation procedure and the anodization time as much as possible to facilitate the mobile application.
Examinations with Keyence microscope, Eddy current testing and REM are performed to characterize the layers. The results are shown in table 1. A clear connection between proper cleaning, anodization time, voltage and amperage and the achieved thickness of the anodized layer is significant. Cracks in the layer show that raising the voltage and amperage results in thicker layers but as well in a crumbled and less stable anodized surface.
Gel preparation:
In addition to the anodization process with a liquid e.g. sulfuric acid a gel application is tested to prevent the electrolyte from rinsing down during the mobile application. For this purpose, several gel-forming agents are tested together with their stability in acid systems. It was observed, that the consistency of the gels varies dependent of the time.
Conductivity:
The conductivity of sulfuric acid combined with different gel-systems was measured and compared in order to predict the possible growth of layers during anodic oxidation process.
Further steps:
Determination and optimization of application parameters like voltage, amperage and anodization-time to build up a preferably stable and sufficient thick anodized layer. Examination of gel preparation to guarantee a stable product, enforcing with textile tape for easy application.