Post 198 –by Gautam Shah
The window like its counterpart the door was a solid shuttered opening in clod climates and a latticed one in warm climates. It did not offer any other options. The first alternative was provided by the soft covering like a curtain. It offered translucency of diffused light and privacy, but did not protect the interior from high winds, rains or cold.
The first glass in an opening was the little cast disk fixed in the roofs. The disks were cast in sand shallow pits, and partially ground to improve its translucency. Technologically it was not possible to produce larger disks and of better transparency. Other materials for window covering were leather (as parchment), wax or oil coated woven clothes, thin pieces of alabaster, and in the orients -the paper.
The first window glass ‘panes’ began to be produced after 1st C AD. These were sheets flattened out of blown glass jars or bottles. Two types of glass were flattened, one was the bottom disc and the other was the cylindrical wall of the blown form. Both, however, retained some curvature of the body, and had poor quality. The poor quality resulted from the inferior glass production technology, retention of curvilinear patterns, poor flattening surface, and poor annealing technology (to remove stresses to make it less brittle). Small size and its slightly curved shape made fixing very difficult.
First commercially (16-17C) produced windows glass was broad cylinder sheet. It was known as broad or muff glass. It was formed by cutting a blown glass cylinder sideways and flattening on a table when still hot. It had uneven thickness, lines marks, and was stuck with dust, sand particles, air bubbles. It was produced till 18 C but the process remained in use till 19 C due to its low requirement of technology. Crown Glass which replaced the cylinder glass, was a flattened bottom disk of a blown glass bulb. It was to an extent was clearer. It had high lustre and lesser stuck-on impurities. It had though unique concentric rings.
Large openings were sub-divisioned by mullions of wood, stone or metals. But technologically the glass was not large enough to cover the inter-mullion space. So small pieces of glass were joined by lead, and very occasionally with crude mastic compound of bitumen. The lead joints and mullions both were used to form patterns. The mullions were of stiffer materials, so formed little stiffer or geometric patterns whereas the lead was soft option amenable to floral and artistic linear patterning. The third option, now added, was to exploit glass casting figures, tinge variations, and manufacturing ‘defects’ as colour-texture-transparency variations.
The window in spite of its static form and glass limitations was a very lively interior surface. The builder also realized the importance of quality of light on various orientations. The windows were devised in consideration of the quality of light from various directions, the scheduling of activities within the building, its profile and location (chamfered inside-outside, low level or clerestory). The nature of Interior treatments, such as paintings (fresco, gesso, etc.), murals (marble, glass mosaic, etc.), gilding, wood work, stone cladding, engraved surfacing, etc. were all affected by the quality of glass in the window, and in turn affected the type of glass being used in the windows.