Degradation processes in colourless Roman glass: cases from the Bocholtz burial |
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Authors: | D.J. Huisman S. Pols I. Joosten B.J.H. van Os A. Smit |
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Affiliation: | 1. RACM, National Service for Archaeology, Cultural Landscape and Built Heritage, P.O. Box 1600, 3800 BP Amersfoort, The Netherlands;2. Saxion Hogescholen, P.O. Box 501, 7400 AM Deventer, The Netherlands;3. ICN, Netherlands Institute for Cultural Heritage, P.O. Box 76709, 1070 KA Amsterdam, The Netherlands;4. TNO-Built Environment and Geosciences/National Geological Survey, P.O. Box 80015, 3508 TA Utrecht, The Netherlands;5. Vrije Universiteit Amsterdam, Institute for Geo- and Bio-archaeology, De Boelelaan 1085, 1081 HV Amsterdam, The Netherlands |
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Abstract: | A group of Roman glass objects from the Bocholtz burial in the SW of Limburg (The Netherlands) was found to have been subject to varying degrees of degradation. Many of the 25 colourless glass objects were fragmented to pieces <0.1 cm (“sugared”), whereas the three transparent blue-green glass objects were in near-pristine state. Analyses using SEM, XRF and EDS revealed that the fragmentation was the direct result of the intense leaching of Na2O from the glass structure and its replacement with water. The resulting gel layers with low-Na2O contents and large amounts of water are sensitive to cracking when they dry out. Thin-walled glass appears to be less sensitive to cracking from the resulting stress than thick-walled glass. Local differences in the moisture regime during burial also influence the severity of the glass degradation. Glass with low concentrations of CaO seems to be the most sensitive to this form of degradation. The typical blue-green Roman glass is less sensitive as it generally has considerably higher concentrations of CaO. |
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Keywords: | Gel layer Glass Leaching Degradation Glass colour &ldquo Sugaring&rdquo Soil moisture |
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