Study of a 9th century silver earrings set from Mikulčice: corrosion, conservation and maintenance

Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para obtenção do grau de Mestre em Conservação e Restauro

The presented study deal with the degradation processes of the silver objects, buried for a long time in human graves and with their appropriate methods of conservation and restoration after excavation during archaeological research. It was used for this study a set of earrings from the 9th century A.D. found in Mikulčice, in the southeast of Czech Republic. To understand the mechanisms and process of corrosion and the manufacture and decoration techniques of the earrings was performed: structural study by photo-documentation in the optic stereo-microscope and by radiography, and microstructure and elemental analysis with scanning electron microscopy with energy dispersive X-ray (SEM-EDS). It was also made detailed metallographic analysis of one pure silver earring fragment to study manufacture technique and the buried silver corrosion process. Related to silver earrings set maintenance conditions was study the atmospheric corrosion of silver in museum environments. For that, it was measure the corrosion rate and film thickness by galvanostatic reduction technique, of 15 silver samples placed in exhibition and storage rooms from the National Museum and Museum of Decorative Arts of Prague.