Custos Aeris: New evaluations for the preventive protection of historical art/lead glass (Part 2)

Part 2: Traceability to damage patterns

Below 0 degrees Celsius the glasses are in the frost zone. In artificial glazing this leads to drying out, embrittlement and shrinkage of the gel layer /Hör 06/. 

Above 40 degrees Celsius the gel layer dries out, damages the solidifying agents and damages Paraloid B72. In addition, glass corrosion is exponentially promoted at high relative humidity with a doubling of the rate per 10 degrees temperature increase /Hör 06/. 

Below 40% relative humidity, the gel layer is damaged by drying out, embrittlement and shrinkage /Hör 06/. 

Above 60% relative humidity a sufficient moisture film for corrosion is already potentially present /Hör 2016/. Above 75% relative humidity an exponential increase in glass corrosion takes place /Garrecht 2010 and DBU project Mühlhausen/. In addition, the risk of mould formation increases /Schumacher 2010/.

The following diagrams show over how many hours the system was in the optimal range and how many hours per measurement period the system was in one of the risk zones defined above:

Thermodynamic risk historical art/lead glass on the airgap-side

The historical art/lead glass is exposed to humid air for 8000 hours and only 5000 hours in the optimal range. It is therefore in the exponential range of glass corrosion and mould may occur.

Thermodynamic risk historical art/lead glass on the church-inner side

Inside the church the situation is much better and there is hardly any risk of corrosion and mould. 

The protective glazing is also exposed to the too humid air for about 8000 hours. However, this is not relevant for the damage to the historically valuable lead glazing.

Thermodynamic risk protective glazing in the air-gap


Garrecht, H., Hahn, O. & Kappes, K. e., 2010. model test for gap temperature control at the Divi Blasii church in Mühlhausen, Germany, s.l.: s.n.
Hör, M. u. F. A. e., 2016: Possibilities of climate stabilization for stained glass collections damaged by anthropogenic environmental influences using the example of St. Sebald in Nuremberg, Nuremberg: St. Sebald, Nuremberg.
Hör, M. u. S. J., 2006. building physics investigations on the endangerment of the stained glass inventory in Nuremberg's Sebalduskirche, possibilities and limits of the effectiveness of exterior protective glazing, Nuremberg: s.n.
Schumacher, C. M., 2010. The glazing of the Protestant St. George Chapel in Fuhlenhagen, Koblenz: Büro Dr. Rauch.
Torge, M., 2011: "Exemplary evaluation of restoration and conservation measures for historical glass paintings with severe damage caused by anthropogenic influences", Berlin: Final report DBU Az 27312-45.


This work is a separate continuation of the DBU project DBU file number 30751 "Development and exemplary application of a new sensor system for monitoring the sustainable effectiveness of protective glazing for stained glass endangered by anthropogenic environmental influences using the example of the Wiesenkirche in Soest", which was funded and completed by the DBU. We would like to take this opportunity to thank you once again for supporting the project.

Contact person: 

Michael Robrecht, iXtronics GmbH, Paderborn
Hans Daams, Hajuveda Heritage, Monschau

Direct contact:

Web addresses:



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