Jarrow, Christchurch: replica of lost C E Kempe & Co window, cartooned, painted and installed by Jonathan Cooke ACR
Protecting Stained Glass Windows
Window guards: protection against external impact
Our window guards are made to our specification and from our templates by one of the world's oldest wire working companies who are very local to us. They are made from fully certified AISI 304 or AISI 316 stainless steel: the standard is a weldmesh 3" ½" slot 12 gauge, with 5mm or 6mm perimeter beading, dependent on the application. Each guard is tig welded at each intersection. The standard finish is a semi-matt black high temperature powder coat which minimises the visual impact of a guard to the exterior of a building, when correctly fitted. Our guards are installed by us, using powder coated stainless steel clips and secured with a plugged stainless steel fastener, into masonry joints wherever practicable.
There are some projects for which polycarbonate protection, correctly specified and installed, can be appropriate. We are experienced in the installation of polycarbonate, with stainless steel clips manufactured to our design.
For vulnerable glass to survive in the long term, it should be protected from environmental hazards. An internally ventilated environmental protective system (sometimes referred to as 'isothermal glazing') is internationally recognised as the best means in principle of retarding deterioration to glass and its surface decoration, and is an approximation to museum conditions suitable for church window glass.
There is an increasing body of evidence as to the long term benefits of glazing in a protected system of this kind. Where the historic lead net is structurally sound the panels can be mounted into frames with minimal degree of intervention which is not only sound conservation practice but can also be a cost effective measure, even in the short term as well as over time.
Recent research in the field of glass science strengthens the argument in favour of this type of installation, in that it provides a flow of air around the conserved glass. Glass deteriorates principally due to moisture attack over time. Adjustments in the internal environment might be effected in a number of ways - increased controlled ventilation and maintenance of a constant low temperature: it is, however, now known that deterioration of glasses of all types occurs at even low levels of relative humidity in controlled museum conditions. 'Isothermal' glazing prevents the formation of condensation settlement on the surfaces of the conserved glass and thus retards further deterioration by removing the condensation element of moisture attack. Although the principle is established, each project is unique, and this will be reflected in the details of the design.
There is detailed information on this subject in Historic England's recent publication