A Window made of Gypsum and Glass: Technical Heritage of making Stucco and Glass Latticeworks

Basing on the archaeological evidences, making stucco and glass latticework windows in Iran dates back to the tenth century AD in Nishapur. One of the methods for making this kind of windows is making two-layered perforated stucco with colorful glasses, which is the subject of current study based on analysis and observations on two historical stucco and glass windows preserved in the ICHTO office of Isfahan. Current study uses optical observation and laboratory tests on two cases of historical two-layered perforated stucco windows to characterize the method of work. Wet chemical tests, FTIR spectroscopy, FE-SEM and XRF analysis used on the samples. Results showed the requirement of use of a wooden frame for more stability during forming in big size windows and starting the work on a rigid backing probably covered with oil as release agent. Two layers of gypsum mortar used in this process, which one is more watery and mixed with an organic material to slow down the setting process. After pouring mortar and the first phase of setting, stucco master used a compass to draw the main geometric lines. Then the first layer removed and the master made finer motifs on the second layer inside the frames made by thicker arms of stucco. The last phase was adhering colorful glasses with a gypsum-adhesive paste on the back of perforated part after removing the rigid backing. Coating the window with oil to reduce the vulnerability of gypsum against humidity is a finishing process after setting of mortar. Evidence of oil showed in FTIR analysis on the extracted samples.