Prior to the 16th century, most “windows” were openings in the building covered with thin sheets of horn, paper, or oiled cloth. Only the buildings deemed most important were glazed, generally with small panes of glass that were held in lead strips. Prosperity came in with the Tudor dynasty, and wealth was displayed by the larger size of windows and glazing.
The Italian Renaissance brought an influence on window shape, producing windows that were taller than they were wide, and divided into four panes by a mullion and transom.
The 17th century saw the introduction of the sash window and crown glass – molten glass that is blown into a bubble, pierced, and spun into a disk about four feet in diameter. After cooling, this glass could be cut into panes which had a slightly rippled effect. The use of crown glass ended the used of glazing with lead in wealthy households. The sash window held the glass in place and was capable of being raised and lowered, adding the ability to allow fresh air into the home as well as sunlight.
Due to the fact that crown glass was so expensive, the prominent type of window for most of the population was the casement window with leaded glazing. By the end of the 18th century, window size became more standardized, and glass production techniques evolved to the point that the cost was reduced, allowing for more of the population to add glazing to their homes and buildings.