Review by Celeste Flower, recent graduate of the MA in Stained Glass Conservation and Heritage Management, The University of York
The annual Stained Glass Conservation Spring Master Class took place this year at the King’s Manor, University of York on 4th March. More than 70 delegates attended in the historic surroundings of the Huntingdon Suite to hear presentations on the subject of Environmental Protective Glazing: Recent Projects and New Research.
Delegates were welcomed and the proceedings introduced by Dr Ivo Rauch and Sarah Brown, Course Director for the MA in Stained Glass Conservation and Heritage Management at York and Director of the York Glaziers Trust. Whilst the day began on a sad note, with a minute’s silence and a tribute to recently-deceased Dr Neil Moat, who had spoken at the Master Class just twelve months before, the subsequent proceedings and discussions were lively and forward-looking.
During the morning recent case studies were presented of two very different protective glazing solutions by Tom Küpper and Keith Barley.
Following damage to a section of a thirteenth-century stained glass lancet in Lincoln Cathedral, caused by an intruder, an opportunity presented itself to conserve four medieval windows in their entirety, equipping them with a protective glazing system. Tom Küpper’s study – “The wind and the rain and all that” – explained that together with the glass and lead matrix, medieval wrought-iron lug-bar ferramenta and oak timber sub-frames also required appropriate protection. He described in detail the holistic approach that was taken towards this multi-component project and emphasized that actions taken in the present will always have profound bearings on future conservation.
Keith Barley spoke about “Environmental protection for the Herkenrode glazing in Lichfield Cathedral”, in which he outlined the extensive series of trials that were carried out to determine appropriate materials for use as external glazing in that particular setting. A comprehensive range of images allowed delegates to see the various effects of glazing types and systems on the exterior aesthetic of windows. Keith also called for a move to outlaw the misleading use of the term ‘isothermal’, pointing out that this could refer as much to externally- as to internally-ventilated systems. Others present agreed that it was important to describe protective systems accurately for the benefit of both prospective clients and future conservators.
The afternoon began with consideration of two issues raised by protective glazing.
Dr Sophie Wolf of the Vitrocentre in Romont, Switzerland, presented a paper researched with Dr Stefan Trümpler – “Conflicting priorities: Protective glazing systems in Switzerland in the light of current energy-conservation strategies”. She described how matters of economy and ecology were leading to a drive towards the installation systems of glazing that would act as additional insulation to churches (in particular) and other buildings. A great number of Swiss buildings had been built with protective “storm windows” housed in metal frames. Although generally unventilated, these glazing systems were not airtight, and performed well in safe-guarding the internal windows against mechanical damage and other effects. However, they could not be judged effective as ‘double-glazing’ against heat-loss from buildings, and she emphasized that where clients were under an illusion that new protective glazing might give energy-saving benefits they should be encouraged to look to the insulation of roofs and walls in the first instance.
Fig. 1. Nancy Georgi presenting on The post-conservation monitoring of the Great East Window of York Minster
Expectations of the function of protective glazing may vary from client to client, whilst conservators understand that performance of any system will vary according to climatic conditions. Nancy Georgi of York Glaziers Trust explained how “The post-conservation monitoring of the Great East Window of York Minster” was currently being conducted, following its recent conservation, including the installation of an internally-ventilated system making use of glass with UV-protective properties. She emphasized the importance of regular re-inspection and monitoring of historic protected windows for temperature, relative humidity, dew point, and airflow velocity within the interspaces. The results from the York studies seem to suggest that the performance of the pioneering protective glazing system is very good against external weather conditions, condensation risk and thermal stress due to solar radiation effects.
Two further presentations introduced state of the art materials and equipment to the delegates.
Michael Robrecht of iXtronics GmbH in Paderborn exhibited “New monitoring equipment for stained glass conservators” in the form of a climate and dew point sensor system (Custos Aeris). Designed for ease of instalment, with continuous data logging (in 15 minute intervals) transferred with analysis to the client’s server by mobile-phone technology, the system impressed many of the delegates who felt this was a much-needed step forward in the field of monitoring. Michael answered a great number of questions from the floor, as did Reiner Meindl in the final presentation of the day.
Herr Meindl of Glasshuette Lamberts in Waldsassen spoke about “The Development of New Glasses for Protective Glazing”. He provided samples and specifications of the innovative glasses which his company are now producing to assist conservators with the optimum protection of fragile historic glass in situ. He described the work of developing the mouth-blown UV-protective glass for York Minster’s Great East Window and other projects, including recent prototypes of glass with an infra-red (IR) protective capacity.
The Master Class concluded with a wine reception and the launch of a new edition of Sarah Brown’s Stained Glass at York Minster, (Scala Arts & Heritage Publishers Ltd. 2017) with photography by Nick Teed of YGT, re-issued fittingly in the 50th year of the founding of the Trust itself.