Materialien
Coarse-grained (yellowish) gypsum plaster; colourless glass (partly with a greyish tint); coloured glass (three shades of green, four shades of blue, three shades of yellow, including a bright-orange piece replaced in 2003); several shades of red flashed glass
Technik
Latticework carved into a rectangular stucco panel and inlaid with colourless and coloured sheet glass. The pieces of glass are fixed on the back of the lattice with a thin layer of gypsum plaster 0.5–1.5mm thick. The average thickness of the stucco panel is approximately 23mm. The stucco panel was cast in a wooden frame.
The design of the latticework has two levels: the main motif (level 0) has been carved out of the stucco panel using sharp, knife-like tools and following a template incised in the surface of the panel. Traces of the incisions are still visible in some places on the front. The second level (level –1) shows irregularly spaced, slightly conical perforations that were pierced with a metal or wooden pin in the stucco before it was fully set. The holes are 10–20mm in diameter and slightly tapered towards the back. All holes are backed with colourless glass. The main design and the perforations have been worked in such a way that the incident light is directed downwards into the room.
The glass is either colourless or coloured in the mass; the red pieces are red flashed glass. Concentric structures on the surface of individual pieces are reminiscent of crown glass. Other pieces of glass show elongated, parallel bubbles like those observed in broad-sheet glass. Scratch marks along the edges of some pieces are traces of a glass cutter.
Erhaltungszustand und Restaurierungen
The window is well preserved and was thoroughly restored in 2003. During this intervention, earlier repairs such plaster fillers and metal reinforcements were removed. The restoration measures included the removal of the 2–3mm-thick coat of red paint; cleaning the surface of the stucco lattice (laser cleaning, density: 1.5 J/cm2 at 1064nm), bonding cracks with acrylic resin, and filling lacunae in the stucco lattice with acrylic filler. The repairs were retouched with pigmented acrylic emulsion. In addition, fragile areas were strengthened with gauze and acrylic resin. The original wooden frame was cleaned with solvent and reinforced by adding an aluminium frame.
At the time of restoration, around 80% of the original pieces of glass were preserved. Missing pieces were replaced with new ones, which were attached with cellulose nitrate.