Walmer Castle, Deal, Kent: Analysis of Window Glass

Author(s): David Dungworth, Brice Girbal

This report presents the results of chemical analysis of historic window glass at Walmer Castle. Previous research using laboratory-based techniques has demonstrated the relationship between the chemical composition of glass and its age. This report presents the first attempt to use a portable instrument to analyse historic window glass without damaging it. The benefits and limitations of a portable X-ray fluorescence (pXRF) spectrometer are explored through the analysis of samples of glass which had been analysed previously using laboratory-based techniques. The problems of analysing glass which also has a UV-absorbing film are also assessed through the analysis of 75 panes analysed from both inside and outside surfaces. This shows that the pXRF analysis of glass through a UV-absorbing film is not rewarding. The analysis of 661 of the Walmer Castle window panes is reported and the results are interpreted in relation to previous laboratory-based analyses and the architectural history of Walmer Castle. Four panes of glass are shown to have been made using seaweed ash and so can be dated to c1700–c1835. 235 panes of glass are shown to be made using synthetic soda prior to the introduction of mechanised drawing techniques, ie c1835–c1930. 222 panes of glass are shown to be made after the introduction of mechanised drawing, ie post-c1930. 43 panes of glass are shown to be made from an unusual potassium-calcium silicate glass. This glass includes the pink and purple glass in the dining room. There are few modern analyses of glass of this composition and historic sources provide little information. It is suggested that this glass was imported from Germany or Bohemia.

Report Number:
Research Department Reports
Glass Post Medieval


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