A Fragile Heritage
Aspects of Historic Glass
Cambridge - Wednesday 6th September 2017

Helen Spencer

article posted 4 Apr 2017

Helen Spencer AMA FSA(Scot) (Heriot Watt University)

BSc (Hons) Archaeological Sciences (University of Bradford)

MA Conservation of Historic Objects - Archaeology (University of Durham)

Worked at National Museums Scotland for 12 years in the Conservation, Analytical Research and Collection Management departments, most recently as Collection Care Manager.

Currently a PhD candidate at Heriot Watt University researching Scottish Medieval and Post Medieval window glass and works as a freelance Consultant.

Scottish Medieval Window Glass: Chemical analysis
Helen Spencer* & Craig Kennedy

Heriot Watt University, Riccarton, Edinburgh, EH14 4AS

Unlike most countries in Europe there is no surviving High Medieval window glass still in situ in monastic or ecclesiastic buildings in Scotland. The only remaining window glass from this period are fragments excavated from the archaeological record.

A total of 250 glass shards from 13 sites across Scotland, typologically dated to between the 13th - 15th Centuries were analysed using Scanning Electron Microscopy - Energy Dispersive Spectrometry (SEM-EDS) and 50 samples were analysed by Laser-ablated Inductively Coupled Plasma Mass Spectroscopy (LA-ICP-MS) allowing the characterisation of trace and rare earth elements in Scottish glass of this period for the first time.

The results show that the glass is likely to have been imported from a range of manufacturing sites across Europe, with regional and chronological differences. Most the glass is dated to the 13th or early 14th century and is a potassium rich "forest glass". A transition from forest glass used in the 13th and 14th centuries to the use of high-lime low alkali glass in the 15th and 16th centuries, can be seen. Differences can be seen in the base glass compositions of the coloured glasses of similar date, which suggests they were sourced from specialist manufacturing sites in different regions of Europe. For example, there are two distinct blue glass compositions found at both Elgin and St Andrew's which were made with different recipes and likely to have been sourced from different manufacturing locations.

The paper will discuss similarities and differences in the composition of the glass from the different sites studied. The glass from the monastic sites of Elcho nunnery and Perth Blackfriars (Dominican) have clear compositional differences to the glass from the Cathedral sites of Elgin and St Andrews, despite both having decoration typical of the late 13th and early 14th Centuries. The rare-earth element profiles can be further used to show that different raw material sources were exploited.

This work is the first major study of the composition of high medieval window glass used in Scotland. It shows that glass from several regions in Europe was sourced and imported to Scotland to glaze cathedrals and monastic buildings.