Glass protects Glass at the Cologne Cathedral thanks to SCHOTT AMIRAN® Heritage Protect

NEW: Cologne Cathedral, Germany



The Cologne Cathedral is a World Cultural Heritage Site with windows from seven centuries. It has one of the largest collections of historical stained glass ever with the oldest dating back to the 13th and 14th centuries. Such works of art made of glass not only have decorative and narrative purposes but als let light in, form a barrier to the outside world, and protect interiors from the weather.

The Challenges
Stained glass is perpetually in peril. This begins with their glass surfaces that react sensitively to water and aqueous solutions. The same is true for modern glass, but much more so for medieval glass which is high in calcium and potassium that further reduces its stability and resistance to weather. This is made worse by aggressive pollutants from the ambient air, especially sulfur dioxide. As a result, deposits are formed that can dull or even fully darken medieval glass.
The Solution
Glass experts from SCHOTT in Grünenplan specialized in producing architectural glass with special anti-reflective coatings, have developed a customized optical interference coating.

It uses a complex system of multiple anti-reflective coating layers of different thicknesses and refractive indices. Such anti-reflective systems are normally designed for 90 degree viewing angles to the glass surface. These systems reduce the degree of visual reflection to only about 1 percent, optimize reflected colors and have many applications such as shop windows, displays, picture glazing and showcases. However, viewing angles for protective glazing in historical buildings often deviate significantly from 90 degrees. Viewing windows at angles of around 45 degrees from the Roncalliplatz square at the Cologne Cathedral using glass samples with anti-reflective and optical interference properties from various manufacturers, had noticeably high degrees of reflection and intense color reflection. The anti-reflective system from SCHOTT minimizes these reflections and allows an almost unadulterated view of the original glazing.

In the spring of 2018, the first upper choir windows in the Cologne Cathedral were fitted with the new SCHOTT AMIRAN® Heritage Protect glazing. More windows are to follow.
SCHOTT AMIRAN® Heritage Protect at the Cologne Cathedral
SCHOTT AMIRAN® Heritage Protect
Float glass

The Material

  • SCHOTT AMIRAN® Heritage Protect in 6.76 mm thickness
  • Extremly high transmission and minimal visible reflection (1%, instead of 8% for float glass)
  • Reduction in the level of reflection and colors from unfavorable viewing angles
  • Laminated glass with protection against weathering, UV radiation and mechanical stresses


Please download our Project Report for further project information: