It is not always possible or appropriate to introduce this system into the windows of an ancient building, but if possible and executed with care and consideration, for the appearance of a building and the presentation of the glazing, it is often the best option.
At the Cathedral we have undertaken to design and execute some of the largest Isothermal schemes in the country, gaining the experience needed to offer this conservation technique to the wider community.
The protection of ancient potash based glass from moisture is of great importance if deterioration of the glass surface is to be minimised. The presence of moisture, whether that be condensation internally or rain coupled with possible atmospheric pollutants externally, is the root cause of deterioration; leaching component parts from a glass matrix that at the point of manufacture were often not a homogeneous mixture and therefore contains microscopic imperfections that allow moisture to dissolve water soluble elements within the glass matrix.
Isothermal glazing allows the ancient glass to be protected on the internal elevation of the window structure, with new external glazing protecting the ancient glass from the elements. The inter-space between the two glass surfaces is vented to allow airflow, preventing condensation from forming and rain contacting the ancient glass. This is as close to a museum environment as can be obtained, while leaving the glass in its original setting.
The way in which the Isothermal glazing is applied is different in almost every building and we are always willing to work with conservation bodies and architects to find the best solution for each individual project.
It should be remembered however that protective glazing is an option for the conservator to propose in circumstances where it will benefit glass that is in a deteriorated condition and in need of protection. Protective glazing should not be used as an alternative to the re-leading of well executed stained glass that shows no sign of the deterioration of the glass surface associated with more ancient glasses. There is a time and place for each of the various techniques employed by the glazier/conservator and it is through open minded dialogue that the appropriate way forward is agreed.
We can provide wire guards in black powder coated stainless steel. These can either be woven, a more traditional way of making a guard or weld mesh a more modern alternative. The guards will be made to follow the shape of each in individual stonework opening and be attached to the stonework by means of non-ferrous fixings. If it becomes necessary to protect your windows, black guards that follow the contours of the stonework detail are the best and most unobtrusive option, if the external view of an ancient building is to be maintained.
View the process of re-leading an ancient stained glass panel from rubbing to completed panel here:
A stained glass window in the making >>