Certain time periods were associated with different trends. As glass used to be cheaper than constructing timber bars within a sash window, glazing bars were a cheaper method as making large panes of glass was incredibly difficult and expensive during the Georgian period.
Glazing bars would be up to 35mm thick, often with a flat external face and an ‘ovolo’ moulded internal face (the reason for such a thickness was to support the equally thick and heavy glass). The bars would divide the windows into as many as 16 panes in the upper sash and twenty in the lower.
The 18th century
In the 18th century, at first the sash window altered little, but as the century progressed design evolved: the glass got thinner, they were generally made from Baltic pine and the width of glazing bars slowly reduced. Internal mouldings were of the ‘lamb’s tongue’ type.
At the end of the century glazing bars on fine sashes were as little as 10mm wide. To make glazing bars or whole windows even more slender, experiments were carried out in iron and copper.
The decline of glazing bars
Introduction of plate glass and improved manufacturing processes in the 1770s led to further increase in pane size (similar as you will see along Brighton & Hove’s Brunswick Square) and reduced numbers of the previously popular glazing bars, though the cost meant they were generally the preserve of the rich and were often employed as a show of social status and money.
Often you would have seen the servant quarters (below or above depending on the property) with multiple glazing bars as they were cheaper to make, whereas the living areas would have the more expensive sash windows.
Sashes eventually became less costly and by mid-century they could be found in evermore humble homes. By the end of the century they were standard on even the smallest worker’s dwelling.