Manufacturing Techniques, Deterioration, and Restoration Problems of Traditional Gypsum Windows

Abstract

The use of gypsum windows (revzen), which are decorated upper windows created by placing glass between gypsum plaster frames, have found wide application in Ottoman architecture from religious structures such as mosques and tombs and imperial structures such as palaces and summer palaces to civil structures such as pavilions and mansions. Decorated with fine plaster craftsmanship and coloured glasses, the gypsum windows were used as part of the interior decoration as well as the window. Manufacturing techniques of gypsum windows vary according to their location in the building. It is common to see that the ones with thick frames and glasses are usually mounted to the window openings facing outwards, and that the ones with thinner frames and decorative coloured glasses are generally mounted to the window openings facing inwards. It is also possible to come across examples that can be seen from both sides, on inner walls overlooking the interiors that receive daylight. It was observed in the literature review conducted within the scope of this study that the national and international literature are inadequate in terms of publications regarding the conservation and restoration methods and material analysis of gypsum windows, which have a wide range of use in monumental structures and civil architecture. Likewise, there are few publications on cleaning and consolidation of other architectural gypsum plaster elements. The research questions that arise from the deficiencies in the literature and motivate this study are as follows: What are the deterioration processes in gypsum window components (i.e., gypsum, glass, reinforcement) caused by the location of the window in the building and environmental factors? What are the suitable conservation methods that can be used for cleaning glass and plaster frames in gypsum windows exposed to environmental pollution and degredation? What are the methods that can be used in the repair of glass, gypsum plaster frames and frame reinforcements and, when necessary, in the renewal in accordance with the original state of the artwork? By which methods can the plaster frames in gypsum windows be reinforced permanently, or temporarily in repair work? What are the preventive conservation measures, and care and maintenance operations for gypsum windows? From these points of view, in the present article, material properties, deterioration processes of traditional gypsum windows, and compatible conventional and new methods that can be used in the conservation and restoration interventions of these decorative elements such as cleaning, consolidation and repair were emphasized. Especially, certain methods and materials that can be applied during plaster cleaning and consolidation, which are difficult processes due to the sensitivity of gypsum, and that are available to use in the repair of window glass, which is an essential phase in the glass conservation process, have been discussed both with their positive and negative aspects. Thus, it was aimed to identify the problems related to conservation and restoration of gypsum windows, to propose solutions by discussing and evaluating the methods in the conservation literature and hence contribute to field studies. In this context, following the introduction section, the manufacturing techniques of the gypsum windows are given in detail and systematically in the second section by supporting the reviewed literature information with original application photographs and schematic drawings. In the third section, in the subtitles under the main heading of Causes of Deterioration and Restoration Problems, the sensitive structure of the gypsum caused by its physical and chemical properties, reinforcement corrosion, damage to the wooden frames, pollutants, chemical deterioration of the window glasses, difficulties in the renewal of the windows glasses, and old repairs and renovations were investigated. Restoration Stages of Gypsum Windows were discussed in the fourth section under these subsections: documentation and diagnostics, cleaning of gypsum frames, cleaning of glass, repair, completion and reproduction (renewal) of gypsum frames, conservation and consolidation of gypsum frames, repair of glasses, maintenance and repair of wooden frames. In addition, care and preventive conservation activities that can be realized to reduce the need for restoration works of gypsum windows were included the fifth section. Finally, in the conclusion section, it is aimed to guide future studies by emphasizing the weaknesses, deficiencies and suggested solutions in the conservation and restoration of plaster windows.