Composition of late seventeenth century window glass from Scotland

Samples of glass from four sites in Scotland were analysed using portable X-ray fluorescence. Three of the sites were archaeological excavations in Ullapool, Stirling and Hume Castle, where glass shards were recovered; the fourth site was a historic building, Traquair House, with original window glass in situ. Each of the sites yielded a chemically distinct type of glass that is remarkably consistent across all four locations. Chemically, the glass recovered shares some characteristics with high lime low alkali (HLLA) glass, used throughout the seventeenth century, and some with kelp fluxed glass, used from the late seventeenth century to the 1840s. The glass appears to be a hybrid of both, representing a late seventeenth century transitional phase from one form of alkali flux to another. Possible sources of this glass type are discussed.