The earliest windows were just holes in a wall. Later, windows were covered with animal hide, cloth, or wood. Shutters that could be opened and closed came next. Over time, windows were built that both protected the inhabitants from the elements and transmitted light, using multiple small pieces of translucent material (such as flattened pieces of translucent animal horn, thin slices of marble, or pieces of glass) set in frameworks of wood, iron or lead. In the Far East, paper was used to fill windows. The Romans were the first known to use glass for windows, a technology likely first produced in Roman Egypt—In Alexandria ca. 100 AD, cast glass windows, albeit with poor optical properties, began to appear—but these were small thick productions, little more than blown glass jars (cylindrical shapes) flattened out into sheets with circular striation patterns throughout. It would be over a millennium before a window glass became transparent enough to see through clearly, as we think of it now. Over the centuries techniques were developed to shear through one side of a blown glass cylinder and produce thinner rectangular window panes from the same amount of glass material. This gave rise to tall narrow windows, usually separated by a vertical support called a mullion. Mullioned glass windows were the windows of choice among European well-to-do, whereas paper windows were economical and widely used in ancient China, Korea and Japan. In England, glass became common in the windows of ordinary homes only in the early 17th century whereas windows made up of panes of flattened animal horn were used as early as the 14th century. Noted science historian, author and television show host/producer James Burke attributes the rapid deforestation of Great Britain in the late 1500s to the uptick in production of glazed windows as well as iron cannon production (1st Cast in 1547). He writes further this gave rise to coal for fuel, which spurred iron production, requiring more coal, and more iron, then steam engine pumps, canals… and more iron; all because windows became a middle class commodity in the latter days of the little ice age, one large factor among several leading to the deforesting English woodlands, and the switch over to a coal economy.
Modern-style floor-to-ceiling windows became possible only after the industrial plate glass making processes were perfected. Modern windows are usually filled with glass, although a few are transparent plastic. Read more