Materialien
Gypsum plaster; colourless glass; coloured glass (two shades of green (one replaced in 2003), light blue, yellow); three shades of red flashed glass (one replaced in 2003)
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. The average thickness of the stucco panel is 19–20mm. 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 with sharp, knife-like tools. On the front of the latticework, tool marks are visible in some places. The second level (level –1), which lies 3–4mm below level 0, shows irregularly spaced, conical perforations that were pierced with a metal or wooden pin in the stucco before it was fully set. The holes are approximately 5mm in diameter and slightly tapered towards the back. The distance between the holes is 5–10mm. 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 made of flashed glass. Elongated parallel bubbles indicate that the glass sheets were mouth-blown, possibly using the broad-sheet method.
Erhaltungszustand und Restaurierungen
The window is well preserved and was thoroughly restored in 2003. During this intervention, earlier repairs as well as a thick coat of dark paint were removed. The restoration measures included the 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 gypsum and/or acrylic fillers. The repairs were retouched with pigmented acrylic emulsion. The original wooden frame was cleaned and reinforced by fixing stainless metal plates on the joints of the frame.
At the time of restoration, most of the original pieces of glass were preserved. The few missing pieces were replaced with new ones, which were attached with cellulose nitrate.