Chemical characterisation of Scottish medieval and post medieval window glass

Abstract

In comparison to the rest of Britain and Europe, there has been relatively little research investigating Scottish medieval and post-medieval window glass. It is thought that all glass was imported into Scotland prior to the first known glass furnace being established in 1610 AD. There is limited documentary evidence for the importation of window glass prior to this although there has been more substantial examination of the documentary evidence for the Scottish glass industry in the Post Medieval period. Minimal scientific work to corroborate the documentary evidence for window glass importation and production had been previously carried out. Evidence for window glass in Scotland during the medieval and post medieval period is reviewed and placed in the wider context of window glass production in Europe. A summary of the evidence of window glass production in Scotland up to the first known excavated glasshouse in Scotland is also presented. Previous scientific analysis of medieval window glass from European contexts have been reassessed and a model to provenance location manufacture, based on major elemental composition and rare earth element profiles, is proposed. Glass from the post medieval period is compared to an existing model proposed for English window glass manufacture. Window glass found in Scottish contexts from the 12th – 18th centuries was chemically characterised to shed light on the origin of window glass used in Scotland. Two hundred and forty-nine samples of medieval window glass and two hundred and two samples of post-medieval window glass fragments were analysed by portable-X-Ray Fluorescence (p-XRF), Scanning Electron Microscopy–Energy Dispersive X-ray Spectroscopy (SEM EDS) and fifty nine of these samples were analysed by Laser-ablated Inductively Coupled Mass Spectroscopy (LA-ICP-MS). The main type of glass in the 13th century appears to have been a potassium rich glass made in North Western France (Normandy). However, there was an increase in the use of high lime low alkali (HLLA) glass in Scotland as early as the 14 th century. This glass type was likely made in North-West Germany/Rhineland or in the Lorraine/Argonne region of France. Later monastic sites continued to use this cheaper HLLA glass which was most likely imported into Perth from Bruges and Antwerp in the late 14th and 15th centuries. Coloured glass was still predominantly made in the North West France, although blue coloured glasses were made in a variety of locations using different base glass and colourant recipes. The composition of post medieval window glass primarily follows the English model from the start of the 17th century. Imported HLLA 1 glass is replaced by a HLLA 2 glass manufactured in Britain. The level of strontium increases in HLLA glass during the 17th century with levels higher than seen in similar glass types made in English furnaces, suggesting that kelp was increasingly used during this period as a flux and may be a sign of Scottish manufacture. By the start of the 18th century, a mixed alkali type glass was being made fluxed with kelp., This work therefore represents the largest analytical study of Scottish medieval and post-medieval window glass undertaken and presents insights into the transfer of materials, technologies and trade routes during the period as well as the early glass manufacturing industry in Scotland.