Isothermal Glazing




In addition to regular Conservation techniques, there are stronger, more permanent methods which can be used especially for mediæval glass. This involves taking the glass from its normal position and housing in a phosphorus bronze frame fixed internally in front of new protective, sympathetic glazing to allow weatherproofing and ventilation all round the original glazing.
Theydon Mount, St Michael and All Saints
This West window had to be removed for brick repairs. Upon closer inspection, the previous, and very comprehensive, conservation scheme was shown to have failed. The adhesives used had degraded badly, and there were thunder bugs and many years of water ingress between plates of glass that were meant to protect the Sixteenth Century painted glass. In its then current condition, the ancient glass was in peril of losing its paintwork and degrading at a molecular level.
Following some intensive fund raising, along with some grant aid, the glazing was treated to a full-scale conservation overhaul. This involved the releading of all the panels and the removal of the previous adhesive and double platings. The shields and clusters of painted diamond quarries were releaded separately from their original supporting glazing, which we replaced with laminated glass.
The diamond clusters were mounted forward of their original position by fixing spacer tabs of copper to both the supporting glazing and the clusters to allow airflow between the two. The shields were fitted into bespoke metal frames, which were fixed to glazing bars. These bars were then set into the jambs and mullions to correspond with the original saddle bars, leaving a gap of 25mm between the shields and the original glazing.
Great Burstead, St Mary
Two adjacent 2-light windows with highly decorative heraldic traceries contain many fragments of mediæval glass throughout. The main lights had been releaded sometime in the latter part of the 20th century, including many ancient painted pieces in their borders, many of whose painted surfaces were facing outwards, exposed to the elements. The tracery lights contain fairly complete heraldic shields and eyelets. As all the glazing had been recently releaded, it was more important to use the grant money raised on protecting the ancient glass from any future external impact, rain and condensation. So all the glazing was removed for cleaning, repair and fitting into metal frames which were then fitted about 2” from the original position of the glazing.
Sheets of 6.4mm laminated glass were fitted into the original glazing grooves and cut to correspond with the external saddle bars in order hide the joints. The protective glazing for the quatrefoil tracery lights were shaped from laminated glass, cut to echo the shapes of the main lead lines. This prevents the light reflecting from a single plane of glass, giving a softer, more fragmented reflection; more akin to the effect of the original lights. Using the thin lead surrounding the metal frames, gaps were created top and bottom to allow for airflow along the entire length of the light.
Barley Church, St Margaret of Antioch
The roundel which had been leaded into this 3-light diamond patterned window was beginning to fall apart due to the previous restoration scheme failing and the lead work becoming too weak to support the glass fragments. The main concern was damage from condensation. This church suffers general dampness, leaving all the windows with varying degrees of condensation on their internal surface. Although it was beyond our scope to cure the dampness of the church itself, we could at least save the fragile glass.
This we achieved by removing the roundel from the supporting leaded glazing and replaced it with a matching shape of 6.4mm laminated glass. Once the roundel had been dismantled, cleaned, edge-bonded and releaded, it was mounted forward of its original position by fixing spacer tabs of copper to both the supporting glazing and the roundel, creating a 18mm gap to allow air flow between the two. When the window was re-visited some weeks later, we could clearly see from the external view that the condensation had formed on the diamond glazing but not on the protective laminated glass or the roundel.
Woodham Walter, St Michael the Archangel
This centre apex panel of a 3-light window on the North side of the building was a fairly complete mediæval image of The Reaper. As the only ancient glass in the building, it was decided to protect it from external impact and the elements. We removed the panel from the stone and removed the later, larger leads that had become too weak to support the glass. Retaining the lead holding The Reaper together, we releaded the surrounding glass and fitted an extra wider lead around the perimeter instead of fitting it into a metal frame for fitting onto the stone
Due to its lighter weight, we were able to fit this directly onto the internal stone, forward of the protective glazing which was fitted into the original glazing groove. This was made of kiln-distorted glass which we leaded to the main lines of the original leaded pattern. This softens the external appearance of the new, highly reflective protective glass.