“A whole book about flat glass – isn’t that a bit, well, boring?” asked a colleague when he heard about our plan to initiate and implement a conference and publication on the subject of Glass in Architecture. Four years later, I can say with a clear conscience: No, not at all. Rather, a unique reference work has been created that makes the importance of glass tangible, from historical production to contemporary recycling. After all, if we throw away old windows and glass, we have a lot to lose, not only culturally, but also in terms of energy.

Rapid disappearance of historical glass

What was the impetus for our interdisciplinary collaboration on Glass in Architecture? In our various fields of activity, we have witnessed the rapid disappearance of historical flat glass from historical buildings and their windows, doors and walls over the past few decades.

When historical buildings of particular cultural importance are refurbished, i.e. adapted to today’s needs, monument preservationists, architects, craftsmen and restorers attach great importance to preserving the historical substance of the buildings. For example, a ceiling beam from the 18th century is not removed without good reason.

But it’s a completely different situation when it comes to flat glass. During a refurbishment, the historical windows, and especially the window glass, are often the first things to be replaced. These are seen as weaknesses. The buzzword here is “energetic upgrading”. By insulating or replacing it, homeowners or residents expect to reduce heating costs and increase comfort. The historical windows often have to give way to new, insulated, multi-glazed windows. Historical wooden window frames in listed buildings are partly preserved and “reinforced” with insulating glass; during such renovations, the historical flat glass usually ends up in the waste container.

Energy-efficient refurbishment in the right place

One thing’s for sure: Saving energy is very important in times of climate change and inflation. And it is true that historical buildings and their windows have a small ecological footprint – providing they were built before the fossil energy revolution in 1850, which means that their non-fossil production got by without coal, natural gas and oil. Moreover, in historical buildings, only 10% of the thermal energy is usually lost through the windows, while the majority is lost through walls, ceilings, floors and ventilation.
In other words, we are upgrading buildings that have lived their entire lives on a shoestring, energetically speaking. And we often upgrade in the wrong place by replacing hundred-year-old wood-glass windows with plastic-glass windows that have to be replaced after 20 to 30 years at the latest and are difficult to recycle. Is this sustainable in energy terms? What about the cultural significance of flat glass that is disappearing here?

Not all glass is the same

Most of the glass used in windows manufactured before 1960 has special characteristic features such as bubble inclusions or rippled surfaces as traces of their manufacture. Over the centuries, glassmakers have developed a wide range of techniques, including cylinder blow molding, centrifuging, and drawing and rolling glass – always with the aim of producing glass that is as large, as flat and as transparent as possible. These work processes required an enormous amount of resources: manpower, special technological and craftsmanship know-how and large amounts of energy. A medieval stained glass window or the glazing of a baroque castle therefore cost a fortune. The idea was that the more numerous and larger the windows, the richer the owner.

Today, we often no longer know how certain historical types of glass were made. There are impressive illustrations of how to spin crown glass, for example in the Encyclopedia (1765) by Diderot and d’Alembert. But in the 21st century, nobody has mastered this technology. When such crown glass is removed from a historical building during an energy upgrade, this example of unique technical expertise is lost.

“Windows are the eyes of buildings”

Flat glass in windows, doors and wall surfaces strongly influences how we perceive our environment. Today, we take for granted a flawlessly transparent view without the slightest distortion. But that wasn’t always the case. If you’ve ever looked through such rippled or blown historical window glass, you’ll see the world in a completely different way – and the world you.
Monument preservation recognized the architectural value of historical flat glass at an early stage because “windows are the eyes of buildings”. Glass producers now offer restoration glass, i.e. flat glass or float glass made using old processes with a corresponding “historical” surface coating. The production of such glass is a niche market and expensive compared to industrial mass production. That’s why if you live or work in a house that has historical window glass, you may not have a Picasso, but you do have some important cultural heritage. Appreciate it!

From the interdisciplinary conference in Romont …

We wanted to investigate and discuss the multifaceted significance of flat glass in more detail. The aim of the conference and publication was to bring together researchers from theory and practice, and also to build a bridge between the humanities and natural sciences. In November 2021, more than 100 participants attended the conference at the Vitrocentre Romont to discuss the production, use, preservation and recycling of flat glass. This is the basis for the publication Glass in Architecture, which is due out soon.

… to the book preview in the Freitagsforum Denkmalpflege Bern

Over 25 authors have written essays in German, English and French for this anthology. Their articles deal with the production in pre-industrial times, the use and importance of flat glass in the history of architecture, as well as questions of preservation, repair and recycling of window glass. The result is a multilingual reference work for academics, practitioners and the general public that can be downloaded free of charge via Open Access.
This is a resounding success for us as editors! With Glass in Architecture, we can raise awareness of the fascinating cultural asset of flat glass, its uniqueness and the challenge of preserving it. We therefore believe that the publication and the conclusion of a successful four years of collaboration between three Swiss institutions and numerous academics are reason to celebrate.

On Friday, May 24, 2024, we are inviting you to the book vernissage as part of the Freitagsforum Denkmalpflege series of events. In the main building of the University of Bern, three experts will give short presentations on flat glass, which will be followed by the book presentation and an aperitif.