Windows are an essential part of most buildings, but are often taken for granted. The texture and tint of early window glass can make a significant contribution to the overall character of an historic building. Investigating the chemical composition of window glass using portable XRF allows us to work out the likely date of manufacture, for example, most 18th century window glass was made using the ash of seaweed. This data is then used to work out which panes of glass are likely to be original and which are later repairs and replacements (and when these were done). The results can be provided schematically as colour-coded illustrations which show at a glance which panes are original and which are later. The dating of historic window glass through pXRF analysis can provide custodians and conservators with essential information to help build conservation management plans and develop conservation treatments.
The pXRF analysis of decorated window glass can be used to clearly identify original and later glazing. Here the original 16th-century panes are coded blue and the later replacements in red (18th century) and yellow or beige (19th or 20th century).