Archaeologists carried out excavations in the former abbey of Stavelot in 1992. They uncovered a unique collection of 12th-century Romanesque stained glass windows. Amongst the thousands of pieces and fragments of glass, many were still decorated with grisaille patterns, representing, amongst other things, human and animal heads, drapery elements and inscriptions.
Once excavated, the fragments of glass were quite deteriorated and fragile. By preserving them temporarily in water, the archaeologists were able to consolidate their condition. In 1995, at the request of the Agence wallonne du Patrimoine (AWaP), KIK-IRPA's Glass Studio investigated the most suitable consolidating agent to prevent the fragments from disintegrating during the drying process while still consolidating their condition. They decided to use Polyethylene glycol PEG 4000; an agent generally used to consolidate water-logged wood.
The process has been successful. The fragments can now be handled without risk, and the remains of the grisaille have been preserved. Between 1998 and 2002, almost 2000 fragments were successfully treated. After a lengthy interruption, the last treatment phase is scheduled for 2021-2022.
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